Interstitial Photodynamic Therapy of Brain Tumors

IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL. 16, NO. 4, JULY/AUGUST 2010 841

Interstitial Photodynamic Therapy of Brain TumorsAnn Johansson, Friedrich-Wilhelm Kreth, Walter Stummer, and Herbert Stepp

(Invited Paper)

Abstract—Malignant gliomas are associated with poor progno-sis. Photodynamic therapy (PDT), relying on light-activated tox-icity of a photosensitizer, has been investigated as a means forimproving patient survival. This review presents a summary ofclinical results obtained with PDT using different photosensitiz-ers for treating brain malignancies. Particular emphasis is on theuse of 5-aminolevulinic acid (ALA) induced protoporphyrin IX(PpIX). PpIX is a potent photosensitizer that displays good tumor-selective uptake and characteristic fluorescence. Here, we presentclinical data on PpIX biodistribution and PpIX photobleachingkinetics, indicating high tumor selectivity and rapid photobleach-ing. These data provide the motivation for the use of a dosimetrymodel aiming at a complete consumption of PpIX during PDT.This dosimetry model, referred to as the advanced photobleachingmodel, has been implemented for interstitial PDT (iPDT) relyingon stereotactic positioning of radial light diffusers within the tumorvolume. A summary of preliminary results from our clinical trialon ALA-mediated brain-iPDT is presented. Finally, recent devel-opments of brain-PDT are discussed with respect to their potentialto improve treatment efficacy. We have identified individualizeddosimetry, the use of multiple photosensitizers and the combina-tion of photosensitizer and immune response modifiers as the mostpromising strategies for further preclinical and clinical research.

Index Terms—5-Aminolevulinic acid (ALA), biomedical appli-cations of optical radiation, brain, fluorescence spectroscopy, ma-lignant glioma, optical propagation in absorbing media, photody-namic therapy (PDT).

I. INTRODUCTION

IN THE Western World, the incidence for primary intracra-nial tumors is 4–11 cases per 100 000 [1]. Gliomas, aris-

ing from the supportive brain tissue, account for more than70% of all primary brain tumors [1]. The high-grade gliomasinclude anaplastic astrocytoma (AA, World Health Organiza-tion (WHO) grade III) and glioblastoma multiforme (GBM,WHO grade IV) and are characterized by median survival of36–48 and 12–15 months, respectively [2]. Recurrences areassociated with significantly poorer prognosis. Conventionaltreatment options include surgery, radiation therapy, andchemotherapy. Novel strategies, e.g., convection-enhanced de-livery of immunotoxins and gene therapy, have so far not

Manuscript received August 20, 2009; revised September 11, 2009; acceptedSeptember 23, 2009. Date of publication November 24, 2009; date of currentversion August 6, 2010. This work was supported in part by the Alexandervon Humboldt Foundation, Medac GmbH, Wedel, Germany, and in part by theDeutsche Krebshilfe under Grant 70-2864.

A. Johansson and H. Stepp are with the Laser Research Institute, UniversityClinic Großhadern, 81377 Munich, Germany (e-mail: [email protected]).

F.-W. Kreth is with the Department of Neurosurgery, University ClinicGroßhadern, 81377 Munich, Germany.

W. Stummer is with the Clinic of Neurosurgery, University Clinic Munster,48149 Munster, Germany.

Digital Object Identifier 10.1109/JSTQE.2009.2033606

Fig. 1. Jablonski diagram illustrating transition processes following absorp-tion of light. The PDT effect is caused by type I, i.e., formation of highlyreactive radical ions, and type II, i.e., formation of singlet oxygen, reactions.phos: phosphorescence, ic: internal conversion, ix: intersystem crossing.

shown significant survival advantages in any phase III study [3].Fluorescence-guided resection (FGR), relying on the tumor-selective accumulation of fluorescing protoporphyrin IX (PpIX)following 5-aminolevulinic acid (ALA, trade name Gliolan,Medac, Wedel, Germany), has been shown to improve radi-cality of resection and prolong survival as compared to surgeryperformed with white-light alone [4], [5]. In 2007, the use ofGliolan acquired clinical approval in the European Union (EU)for FGR of residual glioma. Initial clinical experience impliesthe usefulness of FGR also for brain metastases [6]. However,as tumors infiltrate the normal brain adjacent to tumor (BAT)tissue in a diffuse way, it is impossible to surgically remove alltissue containing malignant cells even with fluorescence guid-ance. Recurrences originate from tumor cells, often referred toas guerrilla or satellite cells [7], embedded in the area of edemaor BAT. Hence, alternative treatment concepts are required.

Photodynamic therapy (PDT) has been investigated as apromising treatment modality for various malignant and nonma-lignant conditions. This treatment modality relies on the light-induced activation of a photosensitizer and the subsequent for-mation of different reactive radicals and oxygen species (seeFig. 1), which, in turn, cause cellular damage. The mechanismsbehind the resulting tissue damage are often categorized intothree, interdependent effects; direct cell damage, vascular dam-age, and activation of an immune response. Direct PDT effectsmost often comprise a combination of apoptosis, also referredto as programmed cell death, and necrosis [8]. Usually, the moreacute the damage, the more the path toward cell death is shiftedin favor of necrosis. The PDT-induced appearance of apoptosisand necrosis as well as bystander effects [9], autophagy [10],and other rescue pathways is controlled via a highly complexseries of cellular signaling events, either promoting or antago-nizing cell death. The vascular photosensitivity is related to the

1077-260X/$26.00 © 2009 IEEE

842 IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL. 16, NO. 4, JULY/AUGUST 2010

amount of photosensitizer present in the blood stream [11]–[14].Following the light-induced oxidation, the cytoskeleton of en-dothelial cells of the vessels is rearranged, leading to exposureof the base membrane, platelet binding, and aggregation, andeventually, thrombosis and microvessel occlusion. The bloodflow is thus stopped and the ensuing hypoxia and nutrient de-privation induce local tissue damage. Evidence also exists thatPDT induces a systemic antitumor immune response, whichmight be important for the long-term tumor control [15]–[17].The relative importance of each of these three mechanisms de-pends among other factors on the photosensitizer, the tissue type,the light administration conditions, and the drug–light interval(DLI) [18], [19].

PDT can easily be applied for superficial and readily acces-sible tissues, such as lesions of the skin, lung, bladder, andgastrointestinal tract as well as for targeting the neovasculaturein age-related macular degeneration (AMD). These indicationsare among those for which PDT employing various photosensi-tizers has acquired clinical approval. PDT can be used also forsolid and deeply situated tumors, where interstitial light deliv-ery, referred to as interstitial PDT (iPDT), needs to be employedin order to overcome the difficulties associated with the limitedpenetration depth, often in the range of millimeters, of the ther-apeutic irradiation. Provided good selectivity in photosensitizeruptake between normal and tumor tissue, PDT presents the ad-vantage of being a tumor-selective treatment option. Surround-ing eloquent and sensitive tissue regions might thus be sparedduring therapy and the use of small-diameter optical fibers forlight delivery makes the procedure minimally invasive. PDT caneasily be repeated and might be of great value for patients noteligible for further surgery or radiation therapy.

Here, we will provide an overview of brain-PDT with asummary of published clinical results. iPDT relying on ALA-induced PpIX and an advanced photobleaching dosimetry modelwill be presented, and we conclude by identifying some novelapproaches toward improved treatment efficacy.

II. PDT FOR BRAIN MALIGNANCIES

The first report on PDT for treating human brain malignancyappeared in 1980, where hematoporphyrin derivative (HpD) andpostsurgery intracavity irradiation were employed [20]. HpDand its purified versions photofrin and photosan have since thenbeen the most commonly employed photosensitizers for brain-PDT [21]–[23]. The therapeutic irradiation is most often appliedwithin the surgical cavity following resection. In order to ho-mogenize the light distribution and to limit the maximal fluencerate, the light source is placed within a scattering lipid solutioncontained either in the surgical cavity [23], [24] or inside anintracavity balloon [23]. Some trials report on interstitial lightdelivery where thin optical fibers have been inserted into thetumor mass. This strategy has been employed either as a com-plement to surgical resection [21], [23], or as a stand-alone treat-ment [25]. Table I lists treatment parameters and clinical resultsfor selected clinical trials. Median survival ranges between 8 and19 months for primary GBM and between 3 and 13.5 months forrecurrent GBM. Long-term survivors have also bee observed,

e.g., three-year survival of 41% and 57% for recurrent GBMand AA, respectively [26]. Treatment efficacy has been reportedto improve for higher light dose [26], [27] and photosensitizeruptake [28]. However, the occurrence of treatment-related sideeffects was shown to increase with the applied light dose [29],indicating that this is not a safe strategy toward improved treat-ment outcome. The selectivity of HpD uptake between tumorand normal tissue is limited to 2.5–4:1 [21]. A disrupted blood–brain barrier (BBB), the existence of leaky blood vessels and anassociation to low-density lipoproteins (LDLs) are factors thatmight promote tumor-selective uptake [28], [30]. Drawbacks ofHpD-mediated PDT include the systemic and prolonged pho-tosensitivity (six to eight weeks), the limited tumor-selectivephotosensitizer uptake, and the risk of PDT-induced intracra-nial edema [21]–[23], [26], [29], [31].

Recently, systemic administration of meso-tetra-(hydroxy-phenyl)-chlorin (mTHPC) at a dose of 0.15 mg/kg body weight(b.w.) has been reported to result in good tumor-selective photo-sensitizer uptake (20:1) [32]. mTHPC has also been investigatedfor PDT of malignant brain tumors, resulting in median survivalof nine months as compared to 3.5 months for the matched con-trol group [2]. However, some cases of toxic reactions followingsunlight exposition and one case of transitional brain swellingwere reported.

Brain-PDT employing synthetic porphyrins, or mTHPC, hasnot yet been established as a frequently used treatment optionwithin the neurosurgical community. In searching for possiblereasons one needs to address issues such as efficacy, safety, andpracticability. As can be seen in Table I, the literature containsa relatively large number of clinical studies showing promisingtreatment results with survival times comparable or superior toconventional treatment modalities. However, a large variabilityin treatment efficacy is obvious when surveying these clini-cal results. In terms of safety, one needs to consider the riskof sensitizing normal brain tissue, the possibility of inducingedema and the prolonged generalized photosensitivity follow-ing systemic administration of first generation photosensitizersand mTHPC. Taken together, the large variation of treatment re-sponse, the risks of significant side effects and the considerableeffort associated with introducing a new technique constitutemajor obstacles that have prevented PDT with synthetic por-phyrins to become a broadly accepted treatment alternative formalignant glioma.

III. ALA-MEDIATED BRAIN-PDT

As a consequence of the limitations observed with the first-generation photosensitizers, studies on ALA-mediated brainphotodiagnosis and PDT were initiated at the University Clinicof Munich. ALA is a precursor that is converted into the ac-tual photosensitizer, PpIX, as a part of the endogenous heme-cycle [33]. PpIX generally displays a relatively good tumor-selective uptake, explained by a decreased ferrochelatase activ-ity within cancer cells, thus limiting the conversion efficiencyof PpIX to heme [34], [35]. Additionally, increased activity ofthe rate limiting enzyme porphobilinogen deaminase (PBGD)has been observed in tumor tissue [36] and tumor cell lines [37].

JOHANSSON et al.: INTERSTITIAL PHOTODYNAMIC THERAPY OF BRAIN TUMORS 843

TABLE ICLINICAL RESULTS FOR PDT ON BRAIN TISSUE


Finally, another mechanism contributing to the high selectivityobserved in glioblastoma versus normal brain is related to theinability of ALA to penetrate the intact BBB [38].

The high tumor-selective photosensitizer uptake and the shortperiod of systemic photosensitivity, confining skin sensitizationto less than two days, are some of the advantages derived fromthe use of ALA for brain-PDT. Furthermore, the intracellularsynthesis of the photosensitizer might lead to a reduced riskof sensitizing surrounding tissue via diffusion of the photosen-sitizer due to the peritumoral edema bulk flow. ALA-PDT ofbrain tumors has been investigated as an adjuvant to surgical re-section [39], [40] or, relying on interstitial light delivery understereotactic guidance, as a stand-alone treatment [41]. In thissection, we will start by introducing a simplified PDT dosime-try model, hereafter referred to as the advanced photobleachingdosimetry model, as motivated in situations where high tumor-selective photosensitizer uptake and rapid photobleaching areobserved. Due to scattering and absorption of light, it is difficult,if not impossible, to apply a homogeneous light dose, or fluence,throughout the entire target volume with good discriminationto surrounding normal tissue. Tumor-selective photosensitizeruptake provides a means to increase treatment selectivity. Fur-thermore, if the photosensitizer displays rapid photobleaching,the low photosensitizer concentration possibly existing withinnormal cells might not be enough for the light-induced damageto exceed the lethal threshold dose. It is thus possible to relax therequirements on an accurate light dosimetry and to apply highfluences, thus targeting photosensitized tissue volumes also atlarge distances from the light sources, without causing damageto normal cells within the irradiated region [41], [42]. This fea-ture is of particular importance to brain malignancies due todiffusely invading tumor cells that are spread within large tissuevolumes.

In the following two sections we address the two prerequi-sites, i.e., a high tumor-selective photosensitizer uptake and arapid photobleaching, for applying the advanced photobleachingdosimetry model for ALA-mediated PDT of brain tissue. Theclinical data on photosensitizer distribution and PDT-inducedphotosensitizer bleaching presented in this section thus pro-vides justification for the use of such a dosimetry model. Fur-thermore, in Section III-C, we discuss the risk of light-inducedthermal effects during PDT. Finally, Section III-D presents theclinical protocol employed and the treatment outcomes frominitial feasibility studies for ALA-mediated brain-iPDT.

A. In Vivo PpIX Distribution

As briefly mentioned in Section I, the use of PpIX fluores-cence for FGR has been shown to improve radicality and efficacyof surgery as judged by survival data [6]. Although these resultssupport the notion of tumor-selective PpIX accumulation, theydo not provide detailed information on the PpIX distributionwith respect to tissue histopathology.

Hence, the PpIX distribution was investigated with respect totumor cell density within a clinical phase II study. Fiber-basedfluorescence spectroscopy (see Fig. 2) was employed followingsurgical resection in 19 patients [43]. Four regions of interest

Fig. 2. Setup employed for in vivo fluorescence spectroscopy. Six, circularlyarranged 400-µm diameter fibers guide fluorescence excitation, 400–440 nm,to the tissue, and the central 400-µm diameter fiber collects the fluorescencespectrum. The long-pass filter before the detector, consisting of a spectrometer,allows simultaneous detection of fluorescence and remission at 450 nm. Theinset illustrates raw data (◦) and fit (solid line), where the fit incorporates rawPpIX fluorescence, a broad autofluorescence component peaking at 500 nm(�) and Gaussian peaks at 455 nm (�) and 660 nm (not shown) to account forexcitation remission and photoproducts, respectively (see further [43]).

Fig. 3. Ratio of 635-nm PpIX fluorescence to the 450-nm remission versustumor cell density. The fluorescence and remission amplitudes were obtainedfrom the fit procedure described in connection to Fig. 2. The fluorescence–remission ratios have been normalized with respect to the highest ratio obtainedwithin the “75%–100% tumor cell density” group for each individual patient inorder to account for patient-specific PpIX kinetics.

were investigated: border of strongly fluorescent tumor (n = 3),weakly fluorescent tissue at the suspected infiltration zone, non-fluorescent adjacent tissue, and nonfluorescent tissue at remotesites. In Fig. 3, the photosensitizer fluorescence is plotted againstthe tumor cell density as judged by a blinded pathologist for 143biopsies in 16 evaluable patients. The data presented in Fig. 3indicate that with increasing tumor cell density, fluorescence in-creases, and that the average fluorescence of normal tissue, hereincluding the “0%” and the “1%–25%” groups, is almost twoorders of magnitude lower than the fluorescence of the “75%–100%” group. Furthermore, none of the biopsies with no tumorcells present exhibited more than 9% of the maximum patient-specific fluorescence. PpIX fluorescence was undetectable inmore than half of these cases (8 of 14). Only 9 of 62 samples


Fig. 4. Fluorescence and MRI contrast of tissue remaining post-FGR. “none”:no macroscopically visible red fluorescence; “weak only”: tissue with strongred fluorescence successfully and safely removed, but weakly fluorescent tissueremaining; “strong”: small amounts of strongly red fluorescing tissue left behinddue to safety reasons. Data have been derived from [44].

with tumor cell densities above 50% showed less that 10% ofthe maximum recorded fluorescence. Three of these sampleswere acquired from the only two patients with WHO grade IIItumors, the other six samples originated from three patients withgrade IV tumors. Such cases might thus constitute potential PDTfailures due to insufficient photosensitization.

Another study aimed at studying the correlation between re-maining tumor volume as determined by postoperative, contrast-enhanced MRI, being the standard method to judge radicality ofsurgery, and residual PpIX fluorescence [44], [45]. Postopera-tive MRI was negative in 17 of 52 glioblastoma patients despitedisplaying residual fluorescence, most probably indicating tu-mor remnants (see Fig. 4). One might thus speculate that PpIXfluorescence is a more sensitive tool for detecting malignantglioma as compared to contrast-enhanced MRI. One case withnegative fluorescence but postoperative MRI indicating tumorremnant was observed. However, the site of contrast uptake wasdistant from the resection surface and located within a tissue foldand thus possible PpIX fluorescence could have been visuallyobstructed during surgery. Furthermore, histological examina-tion of the 264 biopsies collected in this study showed only onecase of PpIX fluorescence from nontumor tissue, thus indicatinga high specificity. However, 26 samples from macroscopicallynonfluorescent sites showed diffusely infiltrating tumor cells(n = 21) or solid tumor (n = 5).

In summary, PpIX buildup displays a relatively good cor-relation with tumor cell density where the average ratio oftumor-to-normal PpIX concentration is 50:1. However, caseswith nonsensitized tumor tissue were also observed, thus indi-cating limited PpIX sensitivity. This problem, possibly related tothe ALA kinetics, the status of the BBB and/or the cell-specificbuild up of PpIX, will be discussed in Section IV.

B. In Vivo PpIX Photobleaching

In vivo data have shown that PpIX is rapidly photobleachedduring PDT and displays only minor amounts of photosensi-

Fig. 5. Residual fluorescence intensity following intracavity, post-FGR PDTat different light doses (n = 18) [43].

tive photoproducts [46]. Therefore, the overall phototoxicitydecreases during irradiation and once the PpIX fluorescence hasvanished, continued irradiation has no further PDT effect. Un-der the assumption of time-independent fluence rate distributionand oxygen supply, it might be justifiable to determine the flu-ence necessary to induce more or less complete photobleaching.Photobleaching kinetics was studied post-FGR (20 mg ALA/kgb.w.) during intracavity PDT of primary glioblastomas wherefluorescent tumor tissue could not be radically resected due toeloquent regions in close proximity [43]. The fluorescing tis-sue remnants were irradiated at 200 mW/cm2 with light dosesincreasing from 100 to 200 J/cm2 . Fluorescence spectra wereacquired with the bifurcated fiber setup (see Fig. 2) prior toPDT, at certain time intervals during PDT and at the end ofirradiation. Fig. 5 shows the resulting photobleaching efficacyindicating that 200 J/cm2 is indeed necessary to reliably pho-tobleach PpIX to less than 5% of the initial intensity. It wasalso observed that the average photobleaching rate was rela-tively independent of the total light dose although large inter-patient variations were observed [43]. In this respect, it shouldbe emphasized that the actual fluence inside tissue was signifi-cantly higher than 200 J/cm2 due to backscattering at the tissuesurface, also referred to as the buildup factor as discussed inSection III-C. It was further observed that up to 200 J/cm2

could be delivered to the surgical cavity without side effects.In contrast to the rapid photobleaching observed during PDT,the white light as well as the blue light employed during FGRhas been shown to induce only moderate photobleaching [45].Here, PpIX fluorescence was observed to decay to 36% of theinitial level following 25 and 87 min of blue and white-lightirradiation, respectively.

In summary, these data indicate that PpIX is rapidly photo-bleached during PDT, a characteristic that constitutes the secondof the cornerstones of the proposed advanced photobleachingdosimetry model.


C. Light and Temperature Distributions in Brain Tissue

The light distribution, determined by the absorption (µa) andscattering (µs alternatively µ′

s) coefficients, is an important pa-rameter during brain-PDT as one desires to administer a suffi-cient fluence at the tumor border, possibly also targeting infil-trating tumor cells. Another issue that needs attention is howwell normal brain tissue can withstand the administered fluenceconsidering possible thermal effects due to light absorption. Toaddress these issues, we employed a combination of intraoper-ative measurements and theoretical simulations.

First, the tissue optical parameters of BAT were investigatedby intraoperative measurements of the total diffuse reflectanceand the spatial reflectance profile [47]. Based on data from 11measurements sites in seven patients, the average penetrationdepth δeff = 1/µeff , where µeff = sqrt[3µa(µa+µ′

s)], was deter-mined to 2.83 mm ± 1.19 mm (mean ± standard deviation) at635 nm. Due to differences in refractive index at the tissue–airinterface and multiple scattering, the fluence rate just below atissue surface can be significantly higher than derived solelyfrom the irradiance, an effect referred to as the buildup factor.Monte Carlo simulations were performed for plane wave irradi-ation of tissue characterized by the average optical parametersderived earlier, resulting in a buildup factor of approximately5. Hence, with an incident light dose of 200 J/cm2 , the ac-tual fluence close to the surface could have been as high as1080 J/cm2 during the intracavity PDT trial described in con-nection to Fig. 5. As this light dose was well-tolerated by thepatients and did not result in any side effects, it was employedas the minimal target fluence, i.e., the light dose assumed neces-sary for inducing complete photobleaching during iPDT. MonteCarlo simulations were then performed to model the light dis-tribution also for interstitial light application. Here, the modelincorporated radially emitting cylindrical light diffusers withinhomogeneous tissue characterized by µa = 0.02 mm−1 and µ′

s =2 mm−1 , i.e., corresponding to an average δeff , as previouslymeasured. Fiber output power was kept below 200 mW/cm toavoid thermal effects at the source [25]. Furthermore, we as-sumed 1 h irradiation time as practically feasible, resulting inthe target fluence of 1080 J/cm2 at the 300 mW/cm2 isoflu-ence rate surface. The light-distribution simulations indicatedthat this fluence rate is located approximately 4 mm from thediffuser surface, as shown in Fig. 6 and [41]. Normally, multiplediffusers need to be employed to fully target the entire tumorvolume, and hence, the fluence also in between fibers needsto exceed the threshold level. This enforces a requirement onthe maximal diffuser separation. For example, with four lightsources positioned at the corners of a square, simulations indi-cated that opposing fibers should not be separated by more thanapproximately 9 mm (surface-to-surface) [41].

Second, we addressed the risk of light-induced thermal effectsby performing temperature calculations, as described in [41].Employing these light irradiation parameters, temperature cal-culations were performed, see [41]. The simulations confirmedthat with the light irradiation parameters and optical properties,as described earlier, the maximum temperature remains below42 ◦C with a 9 mm interfiber distance, whereas an interfiber dis-

Fig. 6. Isofluence rates of a cylindrical light diffuser calculated by MonteCarlo simulations [41].

tance of 7 mm may induce an intolerable temperature increase(>43 ◦C). The simulations also indicated that at and below 7mm fiber separation, the maximum temperature was obtained inthe interfiber spacing instead of at the individual fiber surface.

In summary, these simulations indicate that source positionsshould be carefully chosen to fully target the entire tumor vol-ume while at the same time limiting temperature increase dueto light absorption.

D. iPDT—Clinical Results

A feasibility study including ten patients suffering from re-current glioblastoma were treated by means of stereotactic iPDT(see further [41]). Therapeutic irradiation was performed 2–4 hafter oral delivery of 20 mg/kg b.w. ALA, i.e., the same doseas used for FGR. Radial diffusers with 20–30 mm length wereemployed at 200 mW/cm at 633 nm. A 4-W diode laser at633 nm (Ceralas, BioLitec, Jena, Germany) was connected to abeam splitter capable of coupling light into up to six individualfibers for therapeutic light delivery. Total irradiation time was1 h. In this trial, 3-D treatment planning was performed em-ploying combined computed tomography (CT), MRI, and O-(2-[18f]fluoroethyl)-L-tyrosine-positron emission tomography[FET-PET] data. Diffuser lengths and positions were manuallydetermined so as to maximize overlap between tumor volumeand the isofluence at 1080 J/cm2 and at the same time as mini-mizing spatial overlap of the isofluence curves at the thresholdlevel. Care was also taken not to introduce interfiber distancesbelow 9 mm, as discussed in relation to the temperature simula-tion results in the previous section. For pretreatment planning,the average absorption and reduced scattering coefficients, i.e.,µa = 0.02 mm−1 and µ′

s = 2 mm−1 corresponding to the averageδeff , as discussed in the previous section were used.

Fig. 7 shows the Kaplan–Meier survival curve for the tenpatients treated. Perioperative morbidity was not observed, al-though eloquent tissue was immediately adjacent to the treat-ment volume in several cases. MRI at 24 h post-PDT showeda complete resolution of the contrast enhancement within the


Fig. 7. Kaplan–Meier survival curve for the ten patients included in a feasi-bility study on ALA-mediated iPDT [41].

tumor in seven patients and a partial resolution in the otherthree. From this study, a median survival of 15 months and a1-year survival rate of 60% were observed (see also Table I).Four patients lived longer than 24 months and two of them werestill alive at the follow-up at 48 months. The treatment historyof one of the long-term survivors is described comprehensivelyin [48]. The variability in treatment response will be furtherdiscussed in Section IV-D.

IV. DISCUSSION AND NOVEL DEVELOPMENTS

In this section, we will present recent developments in thefield of brain-PDT, also including studies in preclinical phases,with the intent to identify interesting approaches toward improv-ing this treatment modality. Furthermore, the observed limita-tions of ALA-mediated PDT for treating brain malignancies arediscussed, and we speculate on how these can be circumventedwith the aim to improve treatment efficacy and safety.

A. Need for Individualized Dosimetry

Although considerable effort has been invested in the de-termination of appropriate drug and light dosages, studies onthe inter- and intrapatient variations of light distribution, pho-tosensitizer concentration, and oxygen supply have not beentaken into account for clinical brain-PDT. Hence, the risk ofundertreatment due to insufficient light, drug, and/or oxygenlevels within the target geometry, and in particular, at the tumorborder, should not be neglected. In order to determine optimalsource fiber positions, to tailor the PDT dose distribution and tocalculate the necessary irradiation time, one ideally needs infor-mation on the photosensitizer buildup and the patient-specific,spatially heterogeneous optical properties. Furthermore, indi-vidual differences in drug pharmacokinetics might have ma-jor consequences for the optimal DLI both in terms of max-imum photosensitizer concentration and with respect to thetime point of maximum selectivity between tumor and normaltissue.

To overcome these limitations, intraoperative measurementsof the light absorption and scattering coefficients, the pho-

tosensitizer uptake and the tissue oxygenation are necessary.Real-time treatment monitoring based on in vivo spectroscopicmeasurements of the light transmission at the therapeutic wave-length, at the photosensitizer fluorescence wavelength and inthe near-infrared-response (NIR) region, thus related to thehemoglobin absorbance, has been proposed when aiming atimproving treatment outcomes. Clinical trials, for example, onprostate-PDT have employed isotropic [49], bare-ended [50], orcylindrical [51], [52] fibers positioned in preformed channelswithin the tumor for such spectroscopic measurements. In ad-dition, initial clinical data have also been published reportingon the spatial mapping of the optical parameters as well as ofthe relative photosensitizer distribution [50], [52], [53]. Treat-ment monitoring along these lines are of utmost importanceand can be employed to adjust treatment times to induce com-plete consumption of the available photosensitizer. For somephotosensitizers, it is possible to employ light at the therapeu-tic wavelength to induce fluorescence at a longer wavelength.For example, PpIX fluorescence at 705 nm can be excited at635 nm. Hence, no extra light source is required, no additionaldetector fibers are necessary and the tissue region probed bythe fluorescence signal better reflects the treatment volume ascompared to excitation in the ultraviolet wavelength region. Inconnection to PDT dosimetry based on photobleaching kinet-ics, such as the implicit dosimetry model [54], and the advancedphotobleaching model presented herein, it might be of impor-tance to disentangle the influence of the optical properties onthe measured fluorescence signal in order to render fluorescencemeasurements more quantitative. It is also important to identifysituations where a complete photobleaching has been induced,but where the initial PpIX concentration is too low to result ina sufficient amount of PDT-induced singlet oxygen. In this re-spect, we emphasize the importance of absolute photosensitizerconcentration measurements, data that are unfortunately lackingin the literature.

Furthermore, the biological response to the therapeutic irra-diation, in particular the tissue oxygenation status and the bloodflow, holds information of dosimetric importance. As the PDTreaction itself consumes oxygen, tissue hypoxia might be in-duced in the intercapillary space, thus inhibiting further PDT ac-tion. This effect is even more pronounced for vascular-targetedPDT, where the blood flow shutdown might render larger tis-sue volumes hypoxic. Whether this also causes PDT resistanceremains to be elucidated. In order to avoid treatment-inducedhypoxia, one can introduce lower fluence rates or fractionatedirradiation. These concepts have been shown to result in in-creased treatment efficacy in preclinical [55], [56] as well asclinical studies [57], [58]. Depending on type of photosensitizerand treatment setting, online spectroscopy, relying on photo-bleaching kinetics or NIR absorbance, can yield information onwhen to introduce lower fluence rates or irradiation fractiona-tion in order to allow tissue reoxygenation or photosensitizerredistribution.

The potential of individualized dosimetry and real-time treat-ment feedback has not yet been investigated for brain-PDTalthough some publications outlining possible strategies haveappeared. Recently, Yang et al. reported on a setup and initial


data employing combined fluorescence imaging and noncontactpoint spectroscopy during intraoperative photofrin-PDT [59].The authors speculate on the use of the system for individualizedPDT by identifying and targeting fluorescent tissue remainingpost-FGR and/or to employ observed photobleaching kineticsalong the concept of an implicit dosimetry model [54]. Further-more, patient-specific HpD uptake has been shown to correlatewith survival following surgery plus intracavity PDT [28]. Onedrawback of the advanced photobleaching dosimetry model isthe assumption of sufficient PpIX levels and nonlimiting oxygenconcentration throughout the target volume. As photobleachingkinetics depends, for example, on photosensitizer uptake, flu-ence rate, and oxygen concentration [60], treatment monitoringis required to further develop the proposed dosimetry model. InMunich, we are, therefore, currently implementing interstitial,online monitoring of PpIX photobleaching kinetics, as relevantfor the advanced photobleaching dosimetry model, and initialclinical data are awaited. Furthermore, the use of “standardized”optical properties for the pretreatment planning obviously im-plies that the significant interpatient differences, evident fromthe relatively large standard deviations, of the measured δeffare ignored. A more accurate pretreatment dosimetry wouldrequire intraoperative assessment of the patient-specific absorp-tion and scattering parameters. However, we have shown thattreatment planning strategies similar to those used for radia-tion therapy might be useful for stereotactic iPDT where theparallel visualization of isofluence curves and tumor volumehelps the neurosurgeon to optimize source positioning. Thecomplexity of this procedure, also of relevance to brachyther-apy, warrants further research aiming at providing the clinicalcommunity with tools and automated procedures for treatmentplanning.

In general, online treatment monitoring might present sig-nificant potential for improving treatment outcomes but moreclinical data need to be obtained before an appropriate approachcan be identified and exploited to a useful degree.

B. Modified Irradiation Concepts

Another concept being evaluated for brain-PDT relies on lowintracellular photosensitizer concentration and low fluence ratesin order to increase the fraction of cells that undergo apoptosisrather than necrosis. In an in vivo model it has been shown thatthe tumor selectivity of PpIX accumulation can be increasedby applying ALA over a prolonged period and that extensiveapoptosis can be produced, especially at the tumor bound-ary [61], [62]. This concept, referred to as metronomic PDT(mPDT), requires prolonged irradiation times and/or repetitiveirradiation to deliver the intended light dose and to induce thedesired tissue response. To transfer this approach into a clini-cal situation would require implantation of the irradiation fibersinto the tumor for a couple of days and apply light either con-tinuously with a very low fluence rate or in repetitive sessions.Hence, due to technical difficulties, such a procedure will findclinical acceptance only if the therapeutic outcome is signifi-cantly superior to single-treatment protocols.

C. Other Photosensitizers

Most clinical experience with brain-PDT has been acquiredwith the HpD, photofrin, mTHPC, and PpIX, as shown inTable I. Preclinical and clinical studies have investigated otherphotosensitizers, photosensitizer delivery vehicles and photo-sensitizer combinations.

The incorporation of the photosensitizer into liposomes hasbeen investigated with the aim to increase uptake and PDT effi-cacy. Liposome-encapsulated mTHPC [63] has demonstratedincreased photosensitizer concentration and PDT effect inglioblastoma cell lines. Furthermore, in the 9L rat brain tu-mor model the use of nanoparticles with a vasculature targetingpeptide and incorporating photofrin plus an MR imaging con-trast agent, a survival advantage could be observed as comparedto photofrin-PDT alone [64]. However, difficulties associatedwith their clinical use have hitherto restricted nanoparticles topreclinical models.

In an effort to improve the limited membrane permeability ofthe hydrophobic ALA molecule, the more lipophilic ALA estershave been investigated in preclinical models. Equivalent PDTefficacy was observed in tumor cell lines although the hexyl-and butyl-ALA concentrations were 10–20 times lower thanthe ALA concentration [65], [66]. In contrast to these results,intra-venous (i.v.) administration of the methyl and hexyl estersresulted in essentially no PpIX buildup within the tumor regionin the rat C6 glioma model [67]. White matter, such as thecorpus callosum and the capsula interna, did, however, displaystrong PpIX fluorescence, possibly due to penetration of theesters through the BBB and the subsequent accumulation in thelipid-rich white matter. ALA esters thus appear unsuitable fortreatment of malignant glioma.

Hypericin is an interesting candidate for GBM-therapy inmany ways. Apart from its antidepressant effects, it is knownas an inhibitor of protein kinase C [68] and has been reportedto enhance the effectiveness of the chemotherapeutic temozolo-mide [69]. Additionally, it is a potent photosensitizer, as shownfor PDT on human glioblastoma cell lines [70], [71], as well asa radiosensitizer [72], [73]. Unfortunately, there is no clinicalexperience with hypericin-PDT for malignant glioma.

Boronated porphyrin (BOPP) is a relatively nontoxic, am-phiphilic compound that displays good tumor-selective up-take [74]. BOPP has been employed for boron neutron cap-ture therapy (BNCT) to produce intratumoral radiation dam-age. This compound also displays phototoxicity and has thusbeen investigated in a phase I trial for PDT of 28 high-gradeglioma patients [75]. The survival data are encouraging, withoverall median survival of 14 months and a 12-month survivalrate of 56% for nine GBM patients. However, common side ef-fects were skin photosensitivity, nausea, thrombocytopenia, andraized liver function test. Larger clinical trials will hopefullyelucidate the potential of BOPP-mediated PDT.

In an attempt to increase the overall phototoxic response, thecombination of ALA and photofrin has been proposed [40], [76].Here, the standard ALA dosage (20 mg/kg b.w.) was supple-mented with i.v. administration of 2 mg/kg b.w. photofrin. Thiswas then followed by FGR and irradiation of the surgical cavity


at 630 nm and 100 J/cm2 . The light applicator was then leftin place and therapeutic irradiations with 100 J/cm2 were re-peated daily to a total of four treatment sessions with the intentto induce a photosensitizer redistribution within the target vol-ume. Average survival was longer following PDT, 52.8 weeks(n = 13), as compared to standard surgery alone, 24.6 weeks(n = 14). Although this difference was statistically significant,it is difficult to separate the effects of FGR and PDT and tojudge the relative contribution of the two photosensitizers onthe resulting treatment outcome.

The vascular PDT effect might result in an increased BBBpermeability, as has been observed by erythrocyte extravasa-tion and intravascular thrombosis following photofrin-PDT [29].This might hence increase photosensitizer uptake in BAT, in-cluding infiltrating tumor cells, provided exposure to additionalphotosensitizer and/or photosensitizer precursor. Different pho-tosensitizer combinations might thus exploit the vascular PDTeffect to various degrees, whereas multiple ALA applications as-certain availability of ALA within BAT for the following PDTsession(s). However, opening or permanent disruption of theBBB bears the risk of unselective sensitization and induction ofedema.

The effects of PDT on the status of the BBB might also beexploited for enhanced delivery of chemotherapeutics [77]. Anovel concept is photochemical internalization (PCI), relyingon the PDT-induced intracellular release of macromolecules,such as chemotherapeutics, already incorporated into the cellvia endocytosis. PCI has thus been shown to cause localizedBBB opening and increased efficacy of chemotherapy [78].

D. Variability in Treatment Response

The literature contains evidence for long-term survivors, alsofor GBM recurrences, following ALA PDT [41], [48] as wellas photofrin-PDT [22]. One possible explanation for this is thesynergistic effects of PDT and the immune response. It is well-known that PDT is effective in stimulating the host immuneresponse, e.g., by inducing heat-shock proteins and cyto- andchemokines that attract and activate immune cells [15], [17],[79]. PDT-generated tumor vaccines have even been suggestedand proven effective in animal models [80], [81]. Although it isnot yet clear if and to what extent a PDT-induced immune re-sponse contributes to the clinical outcome in brain-PDT, inves-tigation of this aspect is warranted. On the other hand, PDT alsoshows immunosuppressive effects and induces tumor-promotingfactors, such as vascular endothelial growth factor (VEGF), ma-trix metalloproteinases, and cyclooxygenase-2 [82]. Thus, ad-ditional medication that enhances the PDT-induced immune re-sponse and suppresses the PDT-induced tumor-promoting fac-tors may improve the clinical outcome. In particular, a com-bination therapy with anti-VEGF drugs appears quite promis-ing [83], in particular, considering the fact that Bevacizumab wasapproved in May 2009 for the treatment of GBM. Other factorspotentially contributing to the variability in PDT outcome is thedifferential immunocompetence of patients on chemotherapy,the possibly increased sensitivity to chemotherapy followingPDT-induced reduction in tumor mass and tumor cell hetero-

geneity as well as the production of toxic residues, similar tothe “bystander effect” [9], [84], [85].

On the other hand, some patients show no benefit of PDT oriPDT. In discussing such treatment failures, it is an important is-sue to address whether invading cells are sufficiently sensitized.In our clinical phase II trial on PpIX distribution (see SectionIII-A and Fig. 3), up to 15% of the biopsies from the “50% tu-mor cell density” group showed insufficient PpIX-fluorescence,thus indicating potential treatment failures. Similar results havebeen reported by Madsen et al., where significantly lower PpIXfluorescence was observed from invading tumor cells (BT4C) ascompared to bulk tumor rat brain [86]. Furthermore, PDT withsystemic as well as intratumor ALA administration resulted ina lack of long-term survivors. However, when the BT4C cellswhere preincubated with ALA followed by inoculation and im-mediate irradiation, the response was significantly better. Theseobservations might indicate the presence of nonsensitized tumorcells that survive PDT and cause subsequent recurrences.

In addition to none or insufficiently sensitized infiltratingtumor cells, there may be an inherent difference in the re-sponse of individual tumor cells to the combined exposureof drug and light, thus preventing complete phototoxic celldamage. Especially, the stem-like glioma cells, constituting aside population with enhanced activity of the membrane trans-porter ABCG2 [87], may exhibit resistance to ALA-PDT. Infact, ABCG2 has been identified as an efficient transporter ofPpIX out of the cell, thus shielding these cells from oxidativestress [88]. A transient blocking of ABCG2 might be a strategyto improve ALA-PDT response.

E. Risks Associated With Brain PDT

The risk of inducing damage to normal brain via ALA-PDThas been investigated in normal rat brain by increasing the totalirradiance up to 200 J/cm2 [86], [89]. In the absence of pho-tosensitizer, the depth of damage was limited to 0.5 mm anddid not increase following the i.v. administration of ALA at adose of 100 mg/kg b.w. However, with tumors grown from C6-cells, a tumor-limited necrosis up to a depth of 3.7 mm couldbe observed (100 mg/kg b.w. ALA and 100 J/cm2). In contrastto these observations, substantial necrosis has been observedwithin normal rat brain following 250 mg/kg b.w. ALA and in-terstitial light delivery up to 54 J [86]. The appearance of normalbrain damage may thus be a question of drug rather than lightdose. Interestingly, treatment with steroids prevented damage tonormal brain in this study.

The induction of edema might constitute a larger risk for iPDTas compared to intracavity PDT as an increased pressure withinthe intact skull endangers brain function. Although ALA-PDThas been shown to induce edema within tumor tissue that didnot resolve despite steroid therapy in preclinical models [90],[91], our clinical experience reported so far does not indicateany clinically relevant problem with edema-formation and nointervention other than steroid treatment was ever necessary[41], [48].

A potential risk of side effects also arises from false-positivestaining observed via photosensitizer fluorescence, as has been


reported for photofrin at elevated light doses [29]. This effectmight be deduced from photosensitizer leakage into normalbrain tissue at sites of tumor-surrounding edema [92]. For ALA-induced PpIX, reports on false-positive staining are scarce. Inthe study presented in Section III-A, only one out of 212 fluores-cent biopsies failed to show tumor [44]. Clinical spectroscopicmeasurements on tumor-distant cortex, i.e., gray matter, showedsignificantly less than 10% of the median tumor PpIX level [43].This observation appears contradictory to the results observed inthe rabbit VX2-tumor model [93], [94], where PPIX was foundalso in gray matter following administration of 100 mg/kg b.w.ALA. In the clinical setting, all patients with malignant gliomasare pretreated with corticosteroids, usually dexamethasone, at adaily dose of 12 mg, which tightens the BBB, and thus, reducesthe exposure of gray matter to ALA. Furthermore, they are ex-posed to lower doses of ALA (20 mg/kg b.w.). This may explainthe differences between clinical and preclinical PpIX distribu-tion in gray matter. However, as gray matter seems to be moresensitive to ALA-PDT as compared to VX2 tumor tissue [95],the risk of damage to normal gray matter should not be ignoredin the clinical setting.

In contrast to primary tumors, false positives have been ob-served among patients suffering from recurrences [96]. Fromintraoperatively acquired biopsies, including 11 recurrent and25 primary glioblastomas or AAs, Utsuki et al. identified onefalse-positive sample within the primary tumor group but fivefalse-positive samples for the recurrences. On histology, all ofthese cases showed remarkable infiltration of neutrophils, re-active astrocytes or macrophages. False-positive PpIX fluores-cence has also been observed in cases of radiation necrosis andneurodegenerative disease [97]. Although it is not yet clear whattypes of cells accumulate PpIX and to what degree phototoxiceradication of these cells would impair neurological function,ALA-PDT for primary GBM seems safe, whereas caution iswarranted for recurrent GBM.

Finally, another matter of concern is whether PDT at sublethallevels might stimulate cell proliferation and migration. This hasbeen demonstrated in a mouse model where implantation of U87glioma cells led to faster tumor growth in pretreated normal brainas compared to non pretreated brain [98]. On the other hand, ifthe tumor cells themselves are exposed to sublethal PDT, theirinvasive potential is decreased, as has been shown for differenttumor cell lines [99]–[103], also including cell clones resistantto ALA-PDT [104]. Thus, one may conclude that there is littlerisk of stimulating tumor cell migration following PDT.

V. CONCLUSION

Compared to currently available standard and experimentaltreatment options for malignant glioma, PDT appears highlycompetitive. Here, we have mainly focused on iPDT using ALA-induced PpIX and suggested a dosimetry concept that relies oninducing extensive photosensitizer consumption, here referredto as advanced photobleaching dosimetry. Although the treat-ment procedure has not been fully optimized, our preliminaryclinical results with a median survival of 15 months are indeedencouraging. The herein identified technical improvements in-

clude individualization of treatment parameters based on intra-operative measurements of, for example, the photosensitizer flu-orescence, the optical properties of the target tissue, the oxygensupply, the blood flow and the singlet oxygen production. Fi-nally, a more profound understanding of the relevant biologicalmechanisms, such as the microscopic photosensitizer distribu-tion, the cell death mechanisms, the induction of an immuneresponse, the stimulation of angiogenesis and the influence ofPDT on the BBB, should lead to further optimization of treat-ment regimes, e.g., by using appropriate drug combinations andlight delivery conditions.

ACKNOWLEDGMENT

The authors would like to thank W. Beyer, T. Beck, andT. Pongratz for their valuable assistance during the intra-operative procedures, and W. Rachinger, S. Ito, B. Olzowy,and K. Bise for their contributions to the experimental work.R. Baumgartner, H. J. Reulen, and J. Ch. Tonn are acknowl-edged for their kind support and inspiring discussions.

REFERENCES

[1] H. Ohgaki, “Epidemiology of brain tumors,” Methods Mol. Biol.,vol. 472, pp. 323–342, 2009.

[2] H. Kostron, T. Fiegele, and E. Akutana, “Combination of FOSCANmediated fluorescence guided resection and photodynamic therapy asnew therapeutic concept for malignant brain tumours,” Med. LaserAppl., vol. 21, pp. 285–290, 2006.

[3] J. M. Piepmeier, “The future of neuro-oncology,” Acta Neu-rochir. (Wien.), vol. 151, pp. 1343–1348, Jul. 2009.

[4] W. Stummer, U. Pichlmeier, T. Meinel, O. D. Wiestler, F. Zanella, andH. J. Reulen, “Fluorescence-guided surgery with 5-aminolevulinic acidfor resection of malignant glioma: A randomised controlled multicentrephase III trial,” Lancet Oncol., vol. 7, pp. 392–401, May 2006.

[5] U. Pichlmeier, A. Bink, G. Schackert, and W. Stummer, “Resection andsurvival in glioblastoma multiforme: An RTOG recursive partitioninganalysis of ALA study patients,” Neuro Oncol., vol. 10, pp. 1025–1034,Dec. 2008.

[6] A. A. Potapov, D. J. Usachev, V. A. Loshakov, V. A. Cherekaev, V. N.Kornienko, I. N. Pronin, G. L. Kobiakov, P. L. Kalinin, A. G. Gavrilov,W. Stummer, D. A. Golbin, and P. V. Zelenkov, “First experience in 5-ALA fluorescence-guided and endoscopically assisted microsurgery ofbrain tumors,” Med. Laser Appl., vol. 23, pp. 202–208, 2008.

[7] A. Claes, A. J. Idema, and P. Wesseling, “Diffuse glioma growth: AGuerilla war,” Acta Neuropathol., vol. 114, pp. 443–458, Nov. 2007.

[8] N. L. Oleinick, R. L. Morris, and I. Belichenko, “The role of apoptosisin response to photodynamic therapy: What, where, why, and how,”Photochem. Photobiol. Sci., vol. 1, pp. 1–21, 2002.

[9] J. Dahle, S. Bagdonas, O. Kaalhus, G. Olsen, H. B. Steen, and J. Moan,“The bystander effect in photodynamic inactivation of cells,” Biochim.Biophys. Acta, vol. 1475, pp. 273–280, Jul. 2000.

[10] D. Kessel and N. L. Oleinick, “Initiation of autophagy by photodynamictherapy,” Methods Enzymol., vol. 453, pp. 1–16, 2009.

[11] B. W. Henderson and T. J. Dougherty, “How does photodynamic therapywork?” Photochem. Photobiol., vol. 55, pp. 145–157, Jan. 1992.

[12] V. H. Fingar, “Vascular effects of photodynamic therapy,” J. Clin. LaserMed. Surg., vol. 14, pp. 323–328, Oct. 1996.

[13] B. Chen, B. W. Pogue, P. J. Hoopes, and T. Hasan, “Vascular and cellulartargeting for photodynamic therapy,” Crit. Rev. Eukaryot. Gene Expr.,vol. 16, pp. 279–305, 2006.

[14] V. H. Fingar, P. K. Kik, P. S. Haydon, P. B. Cerrito, M. Tseng, E. Abang,and T. J. Wieman, “Analysis of acute vascular damage after photody-namic therapy using benzoporphyrin derivative (BPD),” Br. J. Cancer,vol. 79, pp. 1702–1708, Apr. 1999.

[15] A. P. Castano, P. Mroz, and M. R. Hamblin, “Photodynamic therapy andanti-tumour immunity,” Nat. Rev. Cancer, vol. 6, pp. 535–545, Jul. 2006.

[16] F. H. van Duijnhoven, R. I. Aalbers, J. P. Rovers, O. T. Terpstra, and P. J.Kuppen, “The immunological consequences of photodynamic treatment


of cancer, a literature review,” Immunobiology, vol. 207, pp. 105–113,2003.

[17] M. Korbelik, “PDT-associated host response and its role in the therapyoutcome,” Lasers Surg. Med., vol. 38, pp. 500–508, Jun. 2006.

[18] D. E. J. G. Dolmans, D. Fukumura, and R. K. Jain, “Photodynamictherapy for cancer,” Nature Rev. Cancer, vol. 3, pp. 380–387, 2003.

[19] T. J. Dougherty, C. J. Gomer, B. W. Henderson, G. Jori, D. Kessel,M. Korbelik, J. Moan, and Q. Peng, “Photodynamic therapy,” J. Nat.Cancer Inst., vol. 90, pp. 889–905, Jun. 1998.

[20] C. Perria, T. Capuzzo, G. Cavagnaro, R. Datti, N. Francaviglia, C. Ri-vano, and V. E. Tercero, “First attempts at the photodynamic treatmentof human gliomas,” J. Neurosurg. Sci., vol. 24, pp. 119–129, Jul.?1980.

[21] H. Kostron, A. Obwegeser, and R. Jakober, “Photodynamic therapy inneurosurgery: A review,” J. Photochem. Photobiol. B, vol. 36, pp. 157–168, Nov. 1996.

[22] S. S. Stylli and A. H. Kaye, “Photodynamic therapy of cerebral glioma—A review. Part II—Clinical studies,” J. Clin. Neurosci., vol. 13, pp. 709–717, Aug. 2006.

[23] P. J. Muller and B. C. Wilson, “Photodynamic therapy of brain tumors—A work in progress,” Lasers Surg. Med., vol. 38, pp. 384–389, Jun.2006.

[24] A. H. Kaye, G. Morstyn, and D. Brownbill, “Adjuvant high-dose pho-toradiation therapy in the treatment of cerebral glioma: A phase 1–2study,” J. Neurosurg., vol. 67, pp. 500–505, Oct. 1987.

[25] S. K. Powers, S. S. Cush, D. L. Walstad, and L. Kwock, “Stereotactic in-tratumoral photodynamic therapy for recurrent malignant brain tumors,”Neurosurgery, vol. 29, pp. 688–695, 1991.

[26] S. S. Stylli, A. H. Kaye, L. MacGregor, M. Howes, and P. Rajendra,“Photodynamic therapy of high grade glioma – long term survival,” J.Clin. Neurosci., vol. 12, pp. 389–398, May 2005.

[27] P. J. Muller and B. C. Wilson, “Photodynamic therapy for malignantnewly diagnosed supratentorial gliomas,” J. Clin. Laser Med. Surg.,vol. 14, pp. 263–270, Oct. 1996.

[28] S. S. Stylli, M. Howes, L. MacGregor, P. Rajendra, and A. H. Kaye,“Photodynamic therapy of brain tumours: Evaluation of porphyrin uptakeversus clinical outcome,” J. Clin. Neurosci., vol. 11, pp. 584–596, Aug.2004.

[29] S. Krishnamurthy, S. K. Powers, P. Witmer, and T. Brown, “Optimal lightdose for interstitial photodynamic therapy in treatment for malignantbrain tumors,” Lasers Surg. Med., vol. 27, pp. 224–234, 2000.

[30] C. Perria, M. Carai, A. Falzoi, G. Orunesu, A. Rocca, G. Massarelli,N. Francaviglia, and G. Jori, “Photodynamic therapy of malignant braintumors: Clinical results of, difficulties with, questions about, and futureprospects for the neurosurgical applications,” Neurosurgery, vol. 23,pp. 557–563, Nov. 1988.

[31] P. J. Muller and B. C. Wilson, “Photodynamic therapy of malignant braintumours,” Can. J. Neurol. Sci., vol. 17, pp. 193–198, 1990.

[32] H. Kostron, 12th World Congress of the International PhotodynamicAssociation, Seattle, WA, 2009.

[33] Q. Peng, K. Berg, J. Moan, M. Kongshaug, and J. M. Nesland, “5-Aminolevulinic acid-based photodynamic therapy: Principles and exper-imental research,” Photochem. Photobiol., vol. 65, pp. 235–251, Feb.1997.

[34] M. M. El-Sharabasy, A. M. El-Waseef, M. M. Hafez, and S. A. Salim,“Porphyrin metabolism in some malignant diseases,” Br. J. Cancer,vol. 65, pp. 409–412, 1992.

[35] S. Kaneko, 12th World Congress of the International PhotodynamicAssociation, Seattle, WA, 2009.

[36] S. Collaud, A. Juzeniene, J. Moan, and N. Lange, “On the selectivityof 5-aminolevulinic acid-induced protoporphyrin IX formation,” Curr.Med. Chem. Anti-Cancer Agents, vol. 4, pp. 301–316, May 2004.

[37] J. F. Greenbaum, Y. Gozlan, D. Schwartz, D. J. Katcoff, and Z. Malik,“Nuclear distribution of porphobilinogen deaminase (PBGD) in gliomacells: A regulatory role in cancer transformation,” Br. J. Cancer, vol. 86,no. 6, pp. 1006–1011, 2002.

[38] S. R. Ennis, A. Novotny, J. Xiang, P. Shakui, T. Masada, W. Stummer,D. E. Smith, and R. F. Keep, “Transport of 5-aminolevulinic acidbetween blood and brain,” Brain Res., vol. 959, pp. 226–234, Jan.2003.

[39] H. Stepp, “Fluorescence-guided resections and photodynamic therapy formalignant gliomas using 5-aminolevulinic acid,” in Proc. SPIE, 2005,pp. 547–557.

[40] M. S. Eljamel, C. Goodman, and H. Moseley, “ALA and photofrinfluorescence-guided resection and repetitive PDT in glioblastoma mul-

tiforme: A single centre Phase III randomised controlled trial,” LasersMed. Sci., vol. 23, pp. 361–367, Oct. 2008.

[41] T. J. Beck, F. W. Kreth, W. Beyer, J. H. Mehrkens, A. Obermeier,H. Stepp, W. Stummer, and R. Baumgartner, “Interstitial photody-namic therapy of nonresectable malignant glioma recurrences using 5-aminolevulinic acid induced protoporphyrin IX,” Lasers Surg. Med.,vol. 39, pp. 386–393, Jun. 2007.

[42] T. S. Mang, “Dosimetric concepts for PDT,” Photodiagn. Photodyn.Ther., vol. 5, pp. 217–223, Sep. 2008.

[43] H. Stepp, T. Beck, T. Pongratz, T. Meinel, F. W. Kreth, J. C. Tonn,and W. Stummer, “ALA and malignant glioma: Fluorescence-guidedresection and photodynamic treatment,” J. Environ. Pathol. Toxicol.Oncol., vol. 26, pp. 157–164, 2007.

[44] W. Stummer, A. Novotny, H. Stepp, C. Goetz, K. Bise, and H. J. Reulen,“Fluorescence-guided resection of glioblastoma multiforme by using5-aminolevulinic acid-induced porphyrins: A prospective study in 52consecutive patients,” J. Neurosurg., vol. 93, pp. 1003–1013, 2000.

[45] W. Stummer, S. Stocker, S. Wagner, H. Stepp, C. Fritsch, C. Goetz, A. E.Goetz, R. Kiefmann, and H. J. Reulen, “Intraoperative detection of malig-nant gliomas by 5-aminolevulinic acid-induced porphyrin fluorescence,”Neurosurgery, vol. 42, pp. 518–526, 1998.

[46] H. Stepp, “Fluorescence guided resection for malignant glioma using5-aminolevulinic acid,” in Proc. SPIE, 2006, pp. 474–480.

[47] T. J. Beck, “Clinical determination of tissue optical properties in vivoby spatially resolved reflectance measurements,” in Proc. SPIE, 2003,pp. 96–105.

[48] W. Stummer, T. Beck, W. Beyer, J. H. Mehrkens, A. Obermeier,N. Etminan, H. Stepp, J. C. Tonn, R. Baumgartner, J. Herms, andF. W. Kreth, “Long-sustaining response in a patient with non-resectable,distant recurrence of glioblastoma multiforme treated by interstitial pho-todynamic therapy using 5-ALA: Case report,” J. Neurooncol., vol. 87,pp. 103–109, Mar. 2008.

[49] T. C. Zhu, A. Dimofte, J. C. Finlay, D. Stripp, T. Busch, J. Miles,R. Whittington, S. B. Malkowicz, Z. Tochner, E. Glatstein, andS. M. Hahn, “Optical properties of human prostate at 732 nm mea-sured in vivo during motexafin lutetium-mediated photodynamic ther-apy,” Photochem. Photobiol., vol. 81, pp. 96–105, Jan. 2005.

[50] A. Johansson, J. Axelsson, S. Andersson-Engels, and J. Swartling, “Re-altime light dosimetry software tools for interstitial photodynamic ther-apy of the human prostate,” Med. Phys., vol. 34, pp. 4309–4321, Nov.2007.

[51] R. A. Weersink, A. Bogaards, M. Gertner, S. R. Davidson, K. Zhang,G. Netchev, J. Trachtenberg, and B. C. Wilson, “Techniques for deliveryand monitoring of TOOKAD (WST09)-mediated photodynamic therapyof the prostate: Clinical experience and practicalities,” J. Photochem.Photobiol. B., vol. 79, pp. 211–222, Jun. 2005.

[52] J. Li and T. C. Zhu, “Determination of in vivo light fluence distributionin a heterogeneous prostate during photodynamic therapy,” Phys. Med.Biol., vol. 53, pp. 2103–2114, Apr. 2008.

[53] J. Axelsson, J. Swartling, and S. Andersson-Engels, “In vivo photo-sensitizer tomography inside the human prostate,” Opt. Lett., vol. 34,pp. 232–234, Feb. 2009.

[54] B. C. Wilson, M. S. Patterson, and L. Lilge, “Implicit and explicit dosime-try in photodynamic therapy,” Lasers Med. Sci., vol. 12, pp. 182–199,1997.

[55] I. A. Boere, D. J. Robinson, H. S. de Bruijn, J. Kluin, H. W. Tilanus,H. J. Sterenborg, and R. W. de Bruin, “Protoporphyrin IX fluorescencephotobleaching and the response of rat Barrett’s esophagus following5-aminolevulinic acid photodynamic therapy,” Photochem. Photobiol.,vol. 82, pp. 1638–1644, Nov. 2006.

[56] E. Angell-Petersen, S. Spetalen, S. J. Madsen, C. H. Sun, Q. Peng, S. W.Carper, M. Sioud, and H. Hirschberg, “Influence of light fluence rate onthe effects of photodynamic therapy in an orthotopic rat glioma model,”J. Neurosurg., vol. 104, pp. 109–117, Jan. 2006.

[57] M. B. Ericson, C. Sandberg, B. Stenquist, F. Gudmundson, M. Karls-son, A. M. Ros, A. Rosen, O. Larko, A. M. Wennberg, and I. Rosdahl,“Photodynamic therapy of actinic keratosis at varying fluence rates: As-sessment of photobleaching, pain and primary clinical outcome,” Br. J.Dermatol., vol. 151, pp. 1204–1212, Dec. 2004.

[58] W. J. Cottrell, A. D. Paquette, K. R. Keymel, T. H. Foster, and A. R.Oseroff, “Irradiance-dependent photobleaching and pain in delta-aminolevulinic acid-photodynamic therapy of superficial basal cell car-cinomas,” Clin. Cancer Res., vol. 14, pp. 4475–4483, Jul. 2008.

[59] V. X. Yang, P. J. Muller, P. Herman, and B. C. Wilson, “A multispec-tral fluorescence imaging system: Design and initial clinical tests in


intra-operative photofrin-photodynamic therapy of brain tumors,” LasersSurg. Med., vol. 32, pp. 224–232, 2003.

[60] J. C. Finlay, S. Mitra, M. S. Patterson, and T. H. Foster, “Photobleachingkinetics of photofrin in vivo and in multicell tumour spheroids indicatetwo simultaneous bleaching mechanisms,” Phys. Med. Biol., vol. 49,pp. 4837–4860, Nov. 2004.

[61] S. K. Bisland, L. Lilge, A. Lin, R. Rusnov, and B. C. Wilson, “Metro-nomic photodynamic therapy as a new paradigm for photodynamic ther-apy: Rationale and preclinical evaluation of technical feasibility for treat-ing malignant brain tumors,” Photochem. Photobiol., vol. 80, pp. 22–30,Jul. 2004.

[62] A. Bogaards, A. Varma, K. Zhang, D. Zach, S. K. Bisland, E. H.Moriyama, L. Lilge, P. J. Muller, and B. C. Wilson, “Fluorescence image-guided brain tumour resection with adjuvant metronomic photodynamictherapy: Pre-clinical model and technology development,” Photochem.Photobiol. Sci., vol. 4, pp. 438–442, May 2005.

[63] A. Molinari, C. Bombelli, S. Mannino, A. Stringaro, L. Toccacieli,A. Calcabrini, M. Colone, A. Mangiola, G. Maira, P. Luciani, G. Mancini,and G. Arancia, “m-THPC-mediated photodynamic therapy of malignantgliomas: Assessment of a new transfection strategy,” Int. J. Cancer,vol. 121, pp. 1149–1155, Sep. 2007.

[64] G. R. Reddy, M. S. Bhojani, P. McConville, J. Moody, B. A. Moffat,D. E. Hall, G. Kim, Y. E. Koo, M. J. Woolliscroft, J. V. Sugai, T. D.Johnson, M. A. Philbert, R. Kopelman, A. Rehemtulla, and B. D. Ross,“Vascular targeted nanoparticles for imaging and treatment of brain tu-mors,” Clin. Cancer Res., vol. 12, pp. 6677–6686, Nov. 2006.

[65] H. Hirschberg, C. H. Sun, B. J. Tromberg, and S. J. Madsen, “ALA-and ALA-ester-mediated photodynamic therapy of human gliomaspheroids,” J. Neurooncol., vol. 57, pp. 1–7, Mar. 2002.

[66] S. M. Wu, Q. G. Ren, M. O. Zhou, Q. Peng, and J. Y. Chen, “Proto-porphyrin IX production and its photodynamic effects on glioma cells,neuroblastoma cells and normal cerebellar granule cells in vitro with 5-aminolevulinic acid and its hexylester,” Cancer Lett., vol. 200, pp. 123–131, Oct. 2003.

[67] W. Rachinger, “Untersuchungen zur porphyrin-akkumulation im per-ifokalen gliomgewebe und normalen hirngewebe nach gabe von 5-Aminolavulinsaure,” Ph.D. dissertation, Medizinische Fakultat derLudwig-Maximilians-Universitat zu Munchen, Munchen, Germany,2006.

[68] W. Zhang, R. E. Law, D. R. Hinton, and W. T. Couldwell, “Inhibition ofhuman malignant glioma cell motility and invasion in vitro by hypericin,a potent protein kinase C inhibitor,” Cancer Lett., vol. 120, pp. 31–38,Nov. 1997.

[69] V. Gupta, Y. S. Su, W. Wang, A. Kardosh, L. F. Liebes, F. M. Hofman,A. H. Schonthal, and T. C. Chen, “Enhancement of glioblastoma cellkilling by combination treatment with temozolomide and tamoxifen orhypericin,” Neurosurg. Focus., vol. 20, p. E20, 2006.

[70] M. Sarissky, J. Lavicka, S. Kocanova, I. Sulla, A. Mirossay, P. Miskovsky,M. Gajdos, J. Mojzis, and L. Mirossay, “Diazepam enhances hypericin-induced photocytotoxicity and apoptosis in human glioblastoma cells,”Neoplasma, vol. 52, pp. 352–359, 2005.

[71] R. Ritz, H. T. Wein, K. Dietz, M. Schenk, F. Roser, M. Tatagiba, andW. S. Strauss, “Photodynamic therapy of malignant glioma with hyper-icin: Comprehensive in vitro study in human glioblastoma cell lines,”Int. J. Oncol., vol. 30, pp. 659–667, Mar. 2007.

[72] W. Zhang, L. Anker, R. E. Law, D. R. Hinton, R. Gopalakrishna, Q. Pu,U. Gundimeda, M. H. Weiss, and W. T. Couldwell, “Enhancement ofradiosensitivity in human malignant glioma cells by hypericin in vitro,”Clin. Cancer Res., vol. 2, pp. 843–846, May 1996.

[73] J. T. Wessels, A. C. Busse, M. Rave-Frank, S. Zanker, R. Hermann,E. Grabbe, and G. A. Muller, “Photosensitizing and radiosensitizingeffects of hypericin on human renal carcinoma cells in vitro,” Photochem.Photobiol., vol. 84, pp. 228–235, Jan. 2008.

[74] J. S. Hill, S. B. Kahl, A. H. Kaye, S. S. Stylli, M. S. Koo, M. F. Gonzales,N. J. Vardaxis, and C. I. Johnson, “Selective tumor uptake of a boronatedporphyrin in an animal model of cerebral glioma,” Proc. Nal. Acad. Sci.USA, vol. 89, pp. 1785–1789, Mar. 1992.

[75] M. A. Rosenthal, B. Kavar, S. Uren, and A. H. Kaye, “Promising sur-vival in patients with high-grade gliomas following therapy with a novelboronated porphyrin,” J. Clin. Neurosci., vol. 10, pp. 425–427, Jul.2003.

[76] G. Zilidis, F. Aziz, S. Telara, and M. S. Eljamel, “Fluorescence image-guided surgery and repetitive photodynamic therapy in brain metastaticmalignant melanoma,” Photodiagn. Photodyn. Ther., vol. 5, pp. 264–266, Dec. 2008.

[77] H. Hirschberg, F. A. Uzal, D. Chighvinadze, M. J. Zhang, Q. Peng, andS. J. Madsen, “Disruption of the blood-brain barrier following ALA-mediated photodynamic therapy,” Lasers Surg. Med., vol. 40, pp. 535–542, Oct. 2008.

[78] H. Hirschberg, M. J. Zhang, H. M. Gach, F. A. Uzal, Q. Peng, C. H. Sun,D. Chighvinadze, and S. J. Madsen, “Targeted delivery of bleomycin tothe brain using photo-chemical internalization of clostridium perfringensepsilon prototoxin,” J. Neurooncol., vol. 95, pp. 317–329, Jun. 2009.

[79] Y. G. Qiang, C. M. Yow, and Z. Huang, “Combination of photodynamictherapy and immunomodulation: Current status and future trends,” Med.Res. Rev., vol. 28, pp. 632–644, Jul. 2008.

[80] M. Korbelik, B. Stott, and J. Sun, “Photodynamic therapy-generatedvaccines: Relevance of tumour cell death expression,” Br. J. Cancer,vol. 97, pp. 1381–1387, Nov. 2007.

[81] H. Zhang, W. Ma, and Y. Li, “Generation of effective vaccines againstliver cancer by using photodynamic therapy,” Lasers Med. Sci., vol. 24,pp. 549–552, Jul. 2009.

[82] C. J. Gomer, A. Ferrario, M. Luna, N. Rucker, and S. Wong, “Photo-dynamic therapy: Combined modality approaches targeting the tumormicroenvironment,” Lasers Surg. Med., vol. 38, pp. 516–521, 2006.

[83] J. Dietrich, A. D. Norden, and P. Y. Wen, “Emerging antiangiogenictreatments for gliomas – efficacy and safety issues,” Curr. Opin. Neurol.,vol. 21, pp. 736–744, Dec. 2008.

[84] D. Olivier, S. Douilard, and T. Patrice, “PDT-induced in vitro bystandereffect,” 12th World Congress of the International Photodynamic Asso-ciation, Seattle, WA, vol. 7380, 2009, pp. 73803Y-1–73803Y-7.

[85] A. Chakraborty, K. D. Held, K. M. Prise, H. L. Liber, and R. W. Redmond,“Bystander effects induced by diffusing mediators after photodynamicstress,” Radiat. Res., vol. 172, pp. 74–81, Jul. 2009.

[86] S. J. Madsen, E. Angell-Petersen, S. Spetalen, S. W. Carper, S. A. Ziegler,and H. Hirschberg, “Photodynamic therapy of newly implanted gliomacells in the rat brain,” Lasers Surg. Med., vol. 38, pp. 540–548,2006.

[87] A. M. Bleau, D. Hambardzumyan, T. Ozawa, E. I. Fomchenko, J. T.Huse, C. W. Brennan, and E. C. Holland, “PTEN/PI3K/Akt pathwayregulates the side population phenotype and ABCG2 activity in gliomatumor stem-like cells,” Cell Stem Cell, vol. 4, pp. 226–235, Mar.2009.

[88] J. Susanto, Y. H. Lin, Y. N. Chen, C. R. Shen, Y. T. Yan, S. T. Tsai,C. H. Chen, and C. N. Shen, “Porphyrin homeostasis maintained byABCG2 regulates self-renewal of embryonic stem cells,” PLoS One,vol. 3, p. e4023, 2008.

[89] B. Olzowy, C. S. Hundt, S. Stocker, K. Bise, H. J. Reulen, andW. Stummer, “Photoirradiation therapy of experimental malignantglioma with 5-aminolevulinic acid,” J. Neurosurg., vol. 97, pp. 970–976, Oct. 2002.

[90] H. Hirschberg, S. Spetalen, S. Carper, P. Hole, T. Tillung, and S. Madsen,“Minimally invasive photodynamic therapy (PDT) for ablation of exper-imental rat glioma,” Minim. Invasive Neurosurg., vol. 49, pp. 135–142,Jun. 2006.

[91] S. Ito, W. Rachinger, H. Stepp, H. J. Reulen, and W. Stummer, “Oedemaformation in experimental photo-irradiation therapy of brain tumoursusing 5-ALA,” Acta Neurochir., vol. 147, pp. 57–65, 2005.

[92] W. Stummer, A. Hassan, O. Kempski, and C. Goetz, “Photodynamictherapy within edematous brain tissue: Considerations on sensitizer doseand time point of laser irradiation,” J. Photochem. Photobiol. B, vol. 36,pp. 179–181, Nov. 1996.

[93] L. Lilge, M. C. Olivo, S. W. Schatz, J. A. MaGuire, M. S. Patterson, andB. C. Wilson, “The sensitivity of normal brain and intracranially im-planted VX2 tumour to interstitial photodynamic therapy,” Br. J. Cancer,vol. 73, pp. 332–343, Feb. 1996.

[94] M. Olivo and B. C. Wilson, “Mapping ALA-induced PPIX fluores-cence in normal brain and brain tumour using confocal fluorescencemicroscopy,” Int. J. Oncol., vol. 25, pp. 37–45, Jul. 2004.

[95] L. Lilge and B. C. Wilson, “Photodynamic therapy of intracranial tissues:A preclinical comparative study of four different photosensitizers,” J.Clin. Laser Med. Surg., vol. 16, pp. 81–91, Apr. 1998.

[96] S. Utsuki, H. Oka, S. Sato, S. Shimizu, S. Suzuki, Y. Tanizaki, K. Kondo,Y. Miyajima, and K. Fujii, “Histological examination of false positivetissue resection using 5-aminolevulinic acid-induced fluorescence guid-ance,” Neurol. Med. Chir (Tokyo), vol. 47, pp. 210–213, May 2007.

[97] S. Miyatake, T. Kuroiwa, Y. Kajimoto, M. Miyashita, H. Tanaka, andM. Tsuji, “Fluorescence of non-neoplastic, magnetic resonance imaging-enhancing tissue by 5-aminolevulinic acid: Case report,” Neurosurgery,vol. 61, pp. E1101–E1103, Nov. 2007.


[98] X. Zheng, F. Jiang, M. Katakowski, X. Zhang, H. Jiang, Z. G. Zhang,and M. Chopp, “Sensitization of cerebral tissue in nude mice with pho-todynamic therapy induces ADAM17/TACE and promotes glioma cellinvasion,” Cancer Lett., vol. 265, pp. 177–187, Jul. 2008.

[99] H. Hirschberg, C. H. Sun, T. Krasieva, and S. J. Madsen, “Effects of ALA-mediated photodynamic therapy on the invasiveness of human gliomacells,” Lasers Surg. Med., vol. 38, pp. 939–945, Dec. 2006.

[100] C. M. Au, S. K. Luk, C. J. Jackson, H. K. Ng, C. M. Yow, and S. S. To,“Differential effects of photofrin, 5-aminolevulinic acid and calphostinC on glioma cells,” J. Photochem. Photobiol. B, vol. 85, pp. 92–101,Nov. 2006.

[101] F. Jiang, M. Chopp, M. Katakowski, K. K. Cho, X. Yang, N. Hochbaum,L. Tong, and T. Mikkelsen, “Photodynamic therapy with photofrin re-duces invasiveness of malignant human glioma cells,” Lasers Med. Sci.,vol. 17, pp. 280–288, 2002.

[102] A. Sharwani, W. Jerjes, C. Hopper, M. P. Lewis, M. El Maaytah,H. S. Khalil, A. J. MacRobert, T. Upile, and V. Salih, “Photodynamictherapy down-regulates the invasion promoting factors in human oralcancer,” Arch. Oral Biol., vol. 51, pp. 1104–1111, Dec. 2006.

[103] A. Uzdensky, A. Juzeniene, L. W. Ma, and J. Moan, “Photodynamicinhibition of enzymatic detachment of human cancer cells from a sub-stratum,” Biochim. Biophys. Acta, vol. 1670, pp. 1–11, Jan. 2004.

[104] A. Casas, G. Di Venosa, S. Vanzulli, C. Perotti, L. Mamome,L. Rodriguez, M. Simian, A. Juarranz, O. Pontiggia, T. Hasan, andA. Batlle, “Decreased metastatic phenotype in cells resistant to aminole-vulinic acid-photodynamic therapy,” Cancer Lett., vol. 271, pp. 342–351, Nov. 2008.

Ann Johansson received the M.Sc. degree in engineering physics and thePh.D. degree from the Department of Physics, Lund University, Lund, Sweden,in 2002 and 2007, respectively.

Since March 2008, she has been a Postdoctoral Fellow with the LIFE Center,University Clinic Großhadern, Munich, Germany. She holds an Alexander vonHumboldt Scholarship. She is currently involved in interstitial PDT for brainand prostate malignancies as well as fluorescence diagnostics.

Friedrich-Wilhelm Kreth received the M.D. degree from the Department ofStereotactic Neurosurgery, University of Freiburg, Germany, in 1998.

During 2001, he was the Head of the Stereotactic Unit, Department ofNeurosurgery, University Hospital Großhadern, Munich, where he has been aClinical Professor since 2008. He was engaged in developing a risk model forinterstitial irradiation of low-grade glioma and was involved in the developmentof stereotactic surgical techniques and treatment planning of interstitial PDT inglioblastoma patients. He has pioneered the development of minimally invasivemolecular stereotactic techniques, combining histopathological diagnosis withsmall sample size-adjusted molecular genetic analysis in low- and high-gradeglioma not eligible for open tumor resection.

Walter Stummer received the M.D. degree from Ludwig-Maximilians Uni-versity, Munich, Germany, in 1991.

He has been the Vice Chairman of the Department of Neurosurgery, Uni-versity of Dusseldorf, Dusseldorf, Germany, since 2003. His current researchinterests include neurooncology, where he was one of the pioneers of 5-aminolevulinic acid-induced fluorescence-guided resection (ALA-FGR) andALA-photodynamic therapy (ALA-PDT) for brain tumors. He was the Cochairof the pivotal phase III brain tumor approval trial on ALA-FGR. He has authoredor coauthored more than 60 peer-reviewed papers in the field of neurooncologyand vascular neurosurgery.

Herbert Stepp received the Ph.D. degree in 1993.He has been a Research Group Leader with the LIFE Center, University

Clinic Großhadern, Munich, Germany, since 1995. His current research interestsinclude optical-tissue diagnostics, photodynamic therapy (PDT), and medicallaser applications. He was engaged in detection and treatment of cancer inthe bladder, brain, lungs, oral cavity, and cervix. He was also involved in theinvestigation of optical coherence tomography, confocal and two-photon excitedfluorescence endoscopy as tools to complement intraoperative tissue diagnosis.He is the author or coauthor of more than 60 papers and holds 15 patentapplications.

Documents

Interstitial Photodynamic Therapy of Brain Tumors