Research Article Physical and Dosimetric Optimization of Laser …downloads.hindawi.com/journals/bmri/2014/151969.pdf · 2019-07-31 · Physical and Dosimetric Optimization of Laser

Research ArticlePhysical and Dosimetric Optimization of Laser Equipment inDermatology A Preliminary Study

A Soriani1 D DrsquoAlessio1 V Cattelan1 N Cameli2 M Mariano2 S Ungania1

M Guerrisi3 and L Strigari1

1 Medical Physics Laboratory Regina Elena National Cancer Institute 00144 Rome Italy2 Department of Dermatology San Gallicano Institute 00144 Rome Italy3 Department of Physics Tor Vergata University 00173 Rome Italy

Correspondence should be addressed to A Soriani sorianiifoit

Received 25 April 2014 Revised 30 July 2014 Accepted 30 August 2014 Published 15 September 2014

Academic Editor Silvia Moretti

Copyright copy 2014 A Soriani et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

The aim of this preliminary study is to investigate the correlation between clinical set-up at present used in the treatment of specificskin conditions and laser beam absorbed power in the tissue This study focused on the CO

2and Nd-Yag laser equipment used

in the daily clinical practice in the Department of Dermatology of San Gallicano Institute in Rome Different types of tissue-equivalent material with various water and haemoglobin concentrations were tested to evaluate laser beam attenuation powerIn particular thinly sliced pork loin of uniform consistency and without fat was selected for its high content of haemoglobin tomimic human tissues An optical power meter was used to measure the power or energy of a laser beam During measurementsthe tissue equivalent phantoms were positioned on the detector head and the laser beam was orthogonally oriented The results oftwo experimental set-ups are reported here The dependence of residual power (W) as a function of ex vivo tissue thickness (mm)for different laser output powers was studied Data were fitted by a parametric logistic equation These preliminary data allow formore accurately determining the energy fraction released from lasers to the tissues in order to improve clinical outcomes

1 Introduction

Over the last 50 years lasers have been used to treat a largevariety of skin conditions either inflammatory or neoplasticin cosmetic and aesthetic dermatology

These treatments use different laser types classifiedaccording to their tissue target andor tissue interaction Onthe basis of this classification themost commonly used lasersin dermatology are ablative lasers (CO

2-Erbium) vascular

lasers (Nd-Yag KTP and PDL) and pigment lasers (Q-switched Nd-Yag Rubino and Alexandrite) Through theirselective targeting of skin chromophores these lasers havebecome the treatment of choice for a wide range of cutaneouslesions including angiomas telangiectasias lentigo tattoosand acne scars and wrinkles [1 2]

The ever improving design and technology of lasers resultin increased safety and efficacy for patients nonethelesscontinuous training and an evolving knowledge are needed

In fact the penetration of radiation is closely linked tothe laser characteristics and to operative conditions Short-pulse high-peak power (Q-switched or mode-locking) lasersproduce high irradiance in a short time while traditionalcontinuous or long pulsed lasers imply shorter exposuresrepeated over prolonged time periodsThese differentmecha-nisms are likely to produce on the irradiated tissues differentbiological effects that should be taken into consideration toavoid irreversible damage as well as to reduce any potentialhazard

In daily clinical practice the wavelength alone is perhapsless of a determining factor as far as depth of penetrationis concernedmdashwith respect to type of emitter and operatingmode physical design of the applicator and adopted tech-nique A working knowledge of tissue targets and light-tissueinteraction is essential to use laser appropriately as well asto interpret clinical laser parameters As a matter of factthe clinical applications of the laser depend on wavelength

Hindawi Publishing CorporationBioMed Research InternationalVolume 2014 Article ID 151969 5 pageshttpdxdoiorg1011552014151969

2 BioMed Research International

peaks of the laser light pulse durations and target skin tissueabsorption Furthermore histological tissue types (muscleadipose and bone) lesion location and skin phototypeare critical parameters for determining the effects of laserinteraction [3ndash6]

The aim of this study is to define the correlation betweenclinical set-up at present used in the treatment of specificskin conditions and laser beam absorbed power in the tissueAn experimental set-up has been performed using differentsamples simulating human tissues Measurements of energy-power at different depths in the tissue have been carried out inorder to fully understand the effects of tissue-laser interactionfor the optimization of clinical outcomes

It is to be stressed that ex vivo tissue used for the testshas rather different characteristics from those of humantissue being less vascularized and hydrated At any rate theinformation obtained from these experiments can help usbetter understand the power and energy release mechanismsin irradiated tissues

2 Material and Methods

21 Lasers Our attention was devoted to the laser equipmentused in the daily clinical practice in the Department ofDermatology of San Gallicano Institute in Rome namelytraditional CO

2laser and Nd-Yag laser

Carbon dioxide (CO2) lasers were considered for their

prominent role and broad spectrum of possible uses indermatologic surgery In particular SmartXideDOT (DEKAMELA Calenzano Italy) in the two modes of laser beamdelivery (710158401015840 handpiece or fractional CO

2) is utilized in our

clinical practice In this latter mode the system generatesperfectly controlled energy pulses (DOTs) by managing theenergy per pulse parameter and the DOT spacing betweentwo microscopic wounds (about 05mm) This mode wasnot analyzed in this preliminary study but will be dealt within the future The spot size for the traditional mode underexamination in this study is 65mm

Nd-Yag laser (neodymium-doped yttriumaluminumgar-net) with a wavelength of 1064 nm long pulsed mode and5mm beam diameter was also investigated

22 Tissue-Like Phantoms Different types of tissue-equivalent material with various water and haemoglobinconcentrations were used to evaluate laser beam attenuationpower Haemoglobin concentrations are important becauseof the presence of red chromophores In particular beefwas selected for its high content of haemoglobin (about01mgmL in beef muscle [7]) to mimic well-vascularisedtissues (with human muscle-like chromophores) howeverdue to its lack of uniformity it proves difficult to repeatthe experiments affecting reproducibility All the ex vivomaterial tested was sliced and slice by slice accuratelymeasured with a caliper in the incident areas Loin (fat-freepork loin) characterized by high haemoglobin concentration(red chromophores) and low water concentration (about37 in fat [8] and 58 in dry-cured loin [9]) was selected astest tissue because of its consistency

23 Detection System The detection system (Laser 2000 LtdUK) used in this study had two measuring heads (A-2-D12-HCB and A-200-D60-HPB) for the evaluation of the effectivepower or energy of the incident laser beamThrough conver-sion of absorbed energy into heat the thermal head sensor(thermopile) registered the potential differences (119881output)produced by the thermal gradient generated by lasers andproportional to the incident energy or power

For nonintensive powers A-2-D12-HCB air cooling sys-tem head turned out to be compatible with different lasertypes allowing high resolution studies for medium powerlasers The power ranges from 1mW to 2W while energyranges from 05mJ to 2 J It has a diameter of 12mm and aspectral range from 025 to 11120583m

The A-200-D60-HPB air forced cooling system headcharacterized by a low reflection index results to be moreresistant The power ranges from 100mW to 40W whileenergy ranges from 1 to 200 J It has a diameter of 60mmand a spectral range varying from 025 to 11 120583m However A-200-D60-HPB head resolution is lower than A-2-D12-HCBAll systems are calibrated (3 accuracy) according to NIST(National Institute of Standards and Technology) andor PTB(Physikalisch-Technische Bundesanstalt)

The electronic processing system retrieves all necessarydata elaborated by the software interface LP-EXPLORERThesoftware connected to the head of detection automaticallyrecognizes the head and through a control panel allows themeasurements to be selected andmade All data collected andrecorded are useful to verify the stability of the signal in CWlasers and any anomalies in PW laser directly in the GUI(graphical user interface)

24 Experimental Set-Up Since in clinical applications laserhand piece is generally located next to the patient skin(about 3ndash5mm) during measurements the laser beam waspositioned orthogonally to the system head in contactwith the tissue-equivalent phantoms executing continuouscircular movements

Power measurements with CO2laser were performed

for different thickness (without tissue 16mm 32mm and48mm) Each set of measurements was repeated with threedifferent powers inCWmode (05W 06W 08W) To obtainmore accurate incident power detection a smaller detectorhead (A-2-D12-HCB) was used (Figure 1)

For CO2laser measurements values of maximum min-

imum and mean power (W) tissue thickness (mm) andresidual power (W) were recorded

Energy measurements with Nd-Yag were performed atfive different thicknesses (16mm 32mm 48mm 64mmand 80mm) with the same phantom (Figure 2) An energyfluence of 125 Jcm2 was used The A-200-D60-HPB headis used in this case The values of maximum minimumand mean power (J) energy fluence (Jcm2) tissue thickness(mm) and residual energy (J) were as well recorded

Laser set-up parameters were chosen in agreement withclinicians in order to simulate clinical protocols The max-imum experimental thickness had to be higher than therange (119889max) reducing the residual measured powerenergy

BioMed Research International 3

Figure 1 Experimental set-up used for the ex vivo phantom andsmall head measurements

Figure 2 Experimental set-up used for the ex vivo phantom andlarger head measurements

at a constant value determined by the measuring head(saturation value)

The net residual energy Δ119864 can be calculated for differenttissue thickness as the measured energy value minus thedetermined saturation value

For each measuring point a different laser position on thetissue was selected to obtain independent measurements

25 Fitting Function The following empirical function wasused to fit the experimental data of power and energy againstthickness (119909)

119910 =119870119886119890minus119887119909

1 + 119886119890minus119887119909 (1)

where 119870 is the maximum measured intensity ldquo119886rdquo representsa scale factor and ldquo119887rdquo determines the curve slope

The curve was selected being the logistic behaviourrepresentative of the expected physical phenomena

3 Results and Discussion

Figure 3 shows residual power (W) dependence as a functionof tissue thickness (mm) for three experimental outputpowers using CO

2laser A fit with the expected curves is also

reported (blue red and green lines)It is to be underscored that for thickness gt2mm the

delivered radiation results in being totally absorbed inside

0010203040506070809

0 1 2 3 4 5

Resid

ual p

ower

(W)

Ex vivo tissue thickness (mm)

CO2

Figure 3 Dependence of the residual power (W) as a functionof equivalent-tissue thickness (mm) for three experimental outputpowers forCO

2((blue diamond) 05W (red circle) 06W and (green

triangle) 08W)

0

2

4

6

8

10

12

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Net

resid

ual e

nerg

y (J

)


Nd-YAG laser

Figure 4 Dependence of the net residual energy Δ119864 (J) as afunction of equivalent-tissue thickness (mm) for Nd-Yag ((redcircle) 125 Jcm2)

the dedicated phantom for all levels of power between theexperimental error

The parameters of each power fitted curve are reported inTable 1

As regards measurements with the Nd-YAG laser a cer-tain amount of energy is not absorbed in the first centimeterof tissue and therefore does not contribute to interactionphenomena

Figure 4 represents the dependence of the net residualenergy (Δ119864) in function of the phantom thickness A fit ofexperimental data is also shown (black line)

The saturation level is located next to the 15 J energyvalue This effect is probably overestimated due to the ratherdifferent characteristics of ex vivo and human tissue

It is worth noting that the energy was obtained byconverting the selected energy fluence (125 Jcm2) with thefollowing expression 125 times 120587 times 1199032 where 119903 = 25mm is theradius of laser applicatorThe theoretical value of energy thusobtained was 245 J while the experimental value was 265 JWe could then verify that the average energy value revealedby the power meter head does not differ for more than 10from that of the set value

The parameters of the net residual energy fitted curve arereported in Table 1


Table 1 Parameters of each power fitted curve related to the experimental measurements

Laser type Unit Measured value (W or J) 119886 119887 119870 Point symbollowast

CO2 Power 05 60 26 050

CO2 Power 06 35 26 063CO2 Power 08 40 26 080Nd-Yag Energy 245 45 07 105lowastPoint symbols used in Figures 3 and 4

Other equivalent tissuesmdashham or chicken (data notshown)mdashwere tested in order to mimic different biologicaltissues Low haemoglobin concentration and high waterconcentration strongly affected the measurements because ofthe scatter fraction increasing against depth As a matter offact in such cases the detected power was below the detectionsystem sensitivity level because of the generated high scatterfraction

Data show that only a small fraction of the incidentenergy is absorbed by the tissues

In the CO2laser it is important to establish proper

measurement duration and to acquireat least five measure-ments to check the reproducibility of beam In this case the10600 nm wavelength emitted as continuous beam destroystissue by rapidly heating and vaporizing intracellular waterIt should however be considered that measurements areaffected by an error due to the intrinsic response time ofelectronics higher than tissues response This leads to ageneral overestimation of values

As for the potential application of similar studies in theclinical practice they could be carried out in collaborationwith clinicians with limited costs and relevant time-sparingOur results show that the beam spreading thermal frontis one of the source physical parameters characterizing themechanisms that induce either tissue damage or proper tissueheating depending on thermal tolerance

Thin superficial lesions on the order of hundreds ofmicrons in thickness receive about the same amount oflight throughout their volume due to incident as well asbackscattered light reflected from the underlying tissuesThisbehaviour is a localized effect of laser therapy due to the lightadministered on the tissue surface irradiance in (Wcm2) orfluence in (Jcm2)

In the thick tumour case the aim is to treat the lesionto some desired depth To treat a volume homogeneouslyefficacy ends up to be proportional to the light penetrationdepth which can be obtained by choosing a proper wave-length In both cases the knowledge of the beam planar sizeplays an important role

In particular prolonged exposure to moderate (CW) orlong pulsed levels of light (PW) produces an absorptioneffect and relative irreversible local or peripheral tissuedamage depending on the spreading thermal front Thesebiological effects are different from those associated with theshort-pulse high-peak power in which because of thermalexpansion tissues damage is generated far from the absorbingareaThus in the Q-switched lasers the spreading effect doesnot occur in the absorbing area

Moreover geometrical distortion the ability to reproducethe real dimensions of the focused beam spots at workingdistance is another important parameter Accuracy out ofthe acceptable limits of the geometrical distortion affectsheterogeneity in powerenergy delivery

4 Conclusion

The experimental set-ups analyzed in this study are just afew examples of laser applications in dermatology obtainedusing standard parameters routinely applied in clinical prac-tice These preliminary data stress the importance to moreaccurately know the fraction of released energy from thesystem to the tissues to improve the treatment strategy Themain point is the correlation between physical design of thehand piece the technique used to apply it wavelength andlaser power in determining clinical outcome Our team ofphysicists and physicians will further investigate this relevanttopic to improve therapeutic procedures

Conflict of Interests

The authors have no potential conflict of interests

Acknowledgment

The authors are grateful to Ing Tiziano Zingoni for his kindand meaningful contribution

References

[1] N Cameli M Mariano M Serio and M Ardigo ldquoPrelimi-nary comparison of fractional laser with fractional laser plusradiofrequency for the treatment of acne scars and photoagingrdquoDermatologic Surgery vol 40 no 5 pp 553ndash561 2014

[2] G Ma PWu X Lin et al ldquoNd YAG laser for ldquofractionalrdquo treat-ment of angiofibromasrdquo International Journal of Dermatologyvol 53 no 5 pp 638ndash642 2014

[3] E A Edwards and S Q Duntley ldquoThe pigments and color ofhuman skinrdquo American Journal of Anatomy vol 65 no 1 pp1ndash33 1939

[4] R R Anderson and J A Parrish ldquoThe optics of human skinrdquoJournal of InvestigativeDermatology vol 77 no 1 pp 13ndash19 1981

[5] M J C Van Gemert S L Jacques H J C M Sterenborgand W M Star ldquoSkin opticsrdquo IEEE Transactions on BiomedicalEngineering vol 36 no 12 pp 1146ndash1154 1989

[6] Z Q Zhao and P W Fairchild ldquoDependence of light trans-mission through human skin on incident beam diameter at


different wavelengthsrdquo in Proceedings of the SPIE Laser-TissueInteraction IX vol 3254 pp 354ndash360 1998

[7] P D Warriss and D N Rhodes ldquoHaemoglobin concentrationsin beefrdquo Journal of the Science of Food and Agriculture vol 28no 10 pp 931ndash934 1977

[8] A Papp E Romppanen T Lahtinen A Uusaro M Harmaand E Alhava ldquoRed blood cell and tissue water content inexperimental thermal injuryrdquo Burns vol 31 no 8 pp 1003ndash1006 2005

[9] B M Popkin K E DrsquoAnci and I H Rosenberg ldquoWaterhydration and healthrdquoNutritionReviews vol 68 no 8 pp 439ndash458 2010

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peaks of the laser light pulse durations and target skin tissueabsorption Furthermore histological tissue types (muscleadipose and bone) lesion location and skin phototypeare critical parameters for determining the effects of laserinteraction [3ndash6]

The aim of this study is to define the correlation betweenclinical set-up at present used in the treatment of specificskin conditions and laser beam absorbed power in the tissueAn experimental set-up has been performed using differentsamples simulating human tissues Measurements of energy-power at different depths in the tissue have been carried out inorder to fully understand the effects of tissue-laser interactionfor the optimization of clinical outcomes

It is to be stressed that ex vivo tissue used for the testshas rather different characteristics from those of humantissue being less vascularized and hydrated At any rate theinformation obtained from these experiments can help usbetter understand the power and energy release mechanismsin irradiated tissues

2 Material and Methods

21 Lasers Our attention was devoted to the laser equipmentused in the daily clinical practice in the Department ofDermatology of San Gallicano Institute in Rome namelytraditional CO

2laser and Nd-Yag laser

Carbon dioxide (CO2) lasers were considered for their

prominent role and broad spectrum of possible uses indermatologic surgery In particular SmartXideDOT (DEKAMELA Calenzano Italy) in the two modes of laser beamdelivery (710158401015840 handpiece or fractional CO

2) is utilized in our

clinical practice In this latter mode the system generatesperfectly controlled energy pulses (DOTs) by managing theenergy per pulse parameter and the DOT spacing betweentwo microscopic wounds (about 05mm) This mode wasnot analyzed in this preliminary study but will be dealt within the future The spot size for the traditional mode underexamination in this study is 65mm

Nd-Yag laser (neodymium-doped yttriumaluminumgar-net) with a wavelength of 1064 nm long pulsed mode and5mm beam diameter was also investigated

22 Tissue-Like Phantoms Different types of tissue-equivalent material with various water and haemoglobinconcentrations were used to evaluate laser beam attenuationpower Haemoglobin concentrations are important becauseof the presence of red chromophores In particular beefwas selected for its high content of haemoglobin (about01mgmL in beef muscle [7]) to mimic well-vascularisedtissues (with human muscle-like chromophores) howeverdue to its lack of uniformity it proves difficult to repeatthe experiments affecting reproducibility All the ex vivomaterial tested was sliced and slice by slice accuratelymeasured with a caliper in the incident areas Loin (fat-freepork loin) characterized by high haemoglobin concentration(red chromophores) and low water concentration (about37 in fat [8] and 58 in dry-cured loin [9]) was selected astest tissue because of its consistency

23 Detection System The detection system (Laser 2000 LtdUK) used in this study had two measuring heads (A-2-D12-HCB and A-200-D60-HPB) for the evaluation of the effectivepower or energy of the incident laser beamThrough conver-sion of absorbed energy into heat the thermal head sensor(thermopile) registered the potential differences (119881output)produced by the thermal gradient generated by lasers andproportional to the incident energy or power

For nonintensive powers A-2-D12-HCB air cooling sys-tem head turned out to be compatible with different lasertypes allowing high resolution studies for medium powerlasers The power ranges from 1mW to 2W while energyranges from 05mJ to 2 J It has a diameter of 12mm and aspectral range from 025 to 11120583m

The A-200-D60-HPB air forced cooling system headcharacterized by a low reflection index results to be moreresistant The power ranges from 100mW to 40W whileenergy ranges from 1 to 200 J It has a diameter of 60mmand a spectral range varying from 025 to 11 120583m However A-200-D60-HPB head resolution is lower than A-2-D12-HCBAll systems are calibrated (3 accuracy) according to NIST(National Institute of Standards and Technology) andor PTB(Physikalisch-Technische Bundesanstalt)

The electronic processing system retrieves all necessarydata elaborated by the software interface LP-EXPLORERThesoftware connected to the head of detection automaticallyrecognizes the head and through a control panel allows themeasurements to be selected andmade All data collected andrecorded are useful to verify the stability of the signal in CWlasers and any anomalies in PW laser directly in the GUI(graphical user interface)

24 Experimental Set-Up Since in clinical applications laserhand piece is generally located next to the patient skin(about 3ndash5mm) during measurements the laser beam waspositioned orthogonally to the system head in contactwith the tissue-equivalent phantoms executing continuouscircular movements

Power measurements with CO2laser were performed

for different thickness (without tissue 16mm 32mm and48mm) Each set of measurements was repeated with threedifferent powers inCWmode (05W 06W 08W) To obtainmore accurate incident power detection a smaller detectorhead (A-2-D12-HCB) was used (Figure 1)

For CO2laser measurements values of maximum min-

imum and mean power (W) tissue thickness (mm) andresidual power (W) were recorded

Energy measurements with Nd-Yag were performed atfive different thicknesses (16mm 32mm 48mm 64mmand 80mm) with the same phantom (Figure 2) An energyfluence of 125 Jcm2 was used The A-200-D60-HPB headis used in this case The values of maximum minimumand mean power (J) energy fluence (Jcm2) tissue thickness(mm) and residual energy (J) were as well recorded

Laser set-up parameters were chosen in agreement withclinicians in order to simulate clinical protocols The max-imum experimental thickness had to be higher than therange (119889max) reducing the residual measured powerenergy








119910 =119870119886119890minus119887119909

1 + 119886119890minus119887119909 (1)








0010203040506070809

0 1 2 3 4 5

Resid

ual p

ower

(W)


CO2



triangle) 08W)

0

2

4

6

8

10

12

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Net

resid

ual e

nerg

y (J

)


Nd-YAG laser












CO2 Power 05 60 26 050











4 Conclusion




Acknowledgment


References

















of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of























119910 =119870119886119890minus119887119909

1 + 119886119890minus119887119909 (1)








0010203040506070809

0 1 2 3 4 5

Resid

ual p

ower

(W)


CO2



triangle) 08W)

0

2

4

6

8

10

12

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Net

resid

ual e

nerg

y (J

)


Nd-YAG laser












CO2 Power 05 60 26 050











4 Conclusion




Acknowledgment


References

















of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of



















CO2 Power 05 60 26 050











4 Conclusion




Acknowledgment


References

















of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of


























of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of





















of






Disease Markers



OncologyJournal of





PPAR Research



Journal of

ObesityJournal of
















Documents

Research Article Physical and Dosimetric Optimization of Laser …downloads.hindawi.com/journals/bmri/2014/151969.pdf · 2019-07-31 · Physical and Dosimetric Optimization of Laser