International Journal of Radiation Oncology � Biology � PhysicsS134

331Dual Energy CT: Treatment Planning for Proton and Ion RadiationTherapy Beyond Standard Tissue CompositionC. Tremmel,1 N. Huenemohr,1 B. Krauss,2 H. Schlemmer,1 O. Jaekel,3,1

and S. Greilich1; 1German Cancer Research Center (DKFZ), Medical

Physics in Radiation Oncology, Heidelberg, Germany, 2Siemens AG,

Healthcare Sector, Imaging and Therapy Division, Forchheim, Germany,3University Hospital of Heidelberg, Radiation Oncology and Radiation

Therapy, Heidelberg, Germany

Purpose/Objective(s): Dual energy computed tomography (DECT)

scanners are increasingly available in the clinic today. Most commonly,

they are used for fast image acquisition or advanced techniques such as

virtual native scans and bone removal. But they also provide new ways

for a better tissue characterization. The latter is especially needed in

proton and ion radiation therapy where uncertainties in the CT calibration

jeopardize the potential of high accuracy treatment delivery. When tissues

deviate significantly from water-equivalency (or “standard tissue”),

a single CT number fails as quantifier for proton/ion range. Metal

implants aggravate the situation considerably by being highly non-tissue

equivalent or by inducing severe imaging artifacts. This even leads to the

rejection of patients. Therefore, our study investigates the possible

benefits of DECT for proton and ion radiation therapy treatment

planning.

Materials/Methods: DECT scans with two different photon spectra were

used to compute the electron density and effective atomic number of tissue

surrogates and materials with elevated atomic number. Furthermore,

preclinical reconstruction algorithms with extended CT range and raw data

based beam hardening correction were used for imaging artifact correction

and an improved geometrical characterization. We scanned a series of

tissue equivalent materials, polymers and metal samples in a second

generation DECT scanner. A novel CT data calibration was established,

which relates both DECT parameters to measured ions ranges (270 MeV/u

Carbon).

Results: We extracted the electron densities and effective atomic numbers

of the measured materials. Using this additional information, a better

material differentiation was feasible. Furthermore, we were able to

correlate the effective atomic number to the mean ionization energy which

is crucial for the ion range estimation of materials with higher atomic

number. This allowed us to improve the WEPL predictions not only for

tissue equivalent, but also for non tissue-equivalent materials such PMMA

(from -6.7% to 1%) and Aluminum (11.3% deviation from theoretical

value, which may be further improved). The reconstruction algorithms

used in this study impact the assessment of geometry and artifacts of metal

implants.

Conclusions: DECT imaging offers additional tissue information that can

enhance ion range calculations in materials with non standard elemental

composition. It can provide better geometrical information on metal

implants with less noise and artifacts.

Author Disclosure: C. Tremmel: None. N. Huenemohr: None. B. Krauss:

A. Employee; Siemens AG. H. Schlemmer: None. O. Jaekel: None. S.

Greilich: None.

332In Vitro Dose Enhancement From Gold Nanoparticles During Low-dose-rate Gamma Irradiation With I-125 Brachytherapy SeedsW. Ngwa,1 H. Korideck,2 A. Kimmelman,2 A.I. Kassis,3 R. Kumar,4

S. Sridhar,4 M. Makrigiorgos,1 and R.A. Cormack1; 1Brigham and

Women’s Hospital, Dana-Farber Cancer Institute and Harvard Medical

School, Boston, MA, 2Dana-Farber Cancer Institute and Harvard Medical

School, Boston, MA, 3Harvard Medical School, Boston, MA, 4Northeastern

University, Boston, MA

Purpose/Objective(s): Recent studies have predicted substantial dose

enhancement to tumors when gold nanoparticles (AuNP) are employed as

adjuvants to radiation therapy at kV energies. Because the enhancement

results from processes at kV energies, some studies proposed gold nano-

particle-aided brachytherapy as a radiation therapy approach with potential

to meet technical and clinical requirements for implementation. To the best

of our knowledge, there has been no study providing clear experimental

evidence to corroborate the substantial dose enhancement predictions

when irradiating with low dose rate gamma photons from brachytherapy

sources. This study investigates the in vitro dose enhancement of AuNP

during irradiation of cancer cells by I-125 low dose rate brachytherapy

sources.

Materials/Methods: HeLa cell cultures were incubated with and

without gold nanoparticles (AuNP) in alternate wells of an 8 well-

chamber slide; 4 wells on each slide had cell cultures with AuNP

while 4 wells contained cell cultures with no AuNP. Two slides were

prepared for each experiment: one slide to be irradiated while the

other serves as sham-irradiation control. The cells were irradiated with

gamma photons from I-125 brachytherapy seeds in a plaque contained

in a custom-built irradiation jig. The plaque was designed to achieve

a relatively homogeneous dose distribution in the plane of the cell

culture slide. Four sets of irradiation experiments were conducted at

370C at dose rates ranging from 2.1 cGy/hr to 4.5 cGy/hr. The dose

rates were varied by varying the height of the cell culture slide above

the plaque containing the I-125 seeds. Residual gammaH2AX was

measured 24 hours after irradiation and used to compare the dose

response of the cells with and without AuNP. In addition, the relative

dose enhancement factor (DEF), representing the ratio of the dose to

the cells with and without the presence of AuNP, was estimated from

the data.

Results: From the dose response behavior, the results show that the bio-

logic effect when irradiating with 0.2 mg/mL concentration of AuNP is up

to 2.3 times greater than without AuNP. This major increase in radiation

damage to cancer cells incubated with AuNP corresponds to an estimated

DEF of over 3.5.

Conclusions: Our findings provide the first experimental evidence of

substantial dose enhancement from gold nanoparticles during low dose rate

gamma irradiation from brachytherapy sources. These in vitro study results

provide impetus for further preclinical and clinical investigations in the

development of gold nanoparticle-aided brachytherapy.

Author Disclosure: W. Ngwa: None. H. Korideck: None. A. Kimmelman:

None. A.I. Kassis: None. R. Kumar: None. S. Sridhar: None. M. Makri-

giorgos: None. R.A. Cormack: None.

333Local Targeted Delivery of Micro-size Radiation Therapy-sourceUsing Temperature-sensitive Hydrogel (RT-GEL)Y. Kim, D. Seol, S. Mohapatra, M.K. Schultz, F.E. Domann, and T. Lim;

University of Iowa, Iowa City, IA

Purpose/Objective(s): We propose using a temperature-sensitive

hydroGEL to allow clinicians to perform direct needle-based injection of

micro-size radiation therapy (RT)-sources for localized tumors (RT-GEL).

RT-GEL allows clinicians to perform direct needle-based injection of

micro-size radioactive-sources for localized tumors. For instance, it can

be used for initially not-lumpectomy eligible breast tumor as a form of

neoadjuvant chemotherapy and concurrent RT-GEL boost or for localized

liver cancer.

Materials/Methods: The hydrogel is liquid at room temperature but

almost immediately gels at body temperature. It was generated as an

injectable vehicle to deliver micro-size radioactive-sources by

synthesizing two FDA-approved polymers, Pluronic F-127 (BASF,

Gurney, USA) and animal-free sodium hyaluronate (SH, Shiseido,

Japan). Indium-111 (T1/2 Z 2.8 days, primary gamma ray 862keV)

was tested as a micro-size radioactive source. The radiation effect of

In111 on the characteristics of hydrogel was tested. The injectability

and efficacy of RT-GEL delivery to human breast tumor using the

control datasets of RT-Saline injection were also tested. As proof-of-

concept studies, a total 6 nude mice were tested in which 4 million