Shinhaeng Cho, Youngmoon Goh, Chankyu Kim, Haksoo Kim, Jong Hwi Jeong, Young Kyung Lim, Se Byeong Lee, Dongho Shin

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1 Originl Article PMP Progress in Medicl Physics 28(4), Decemer pissn , eissn Dosimetric Impct of Ti Mesh on Proton Bem Therpy Shinheng Cho, Youngmoon Goh, Chnkyu Kim, Hksoo Kim, Jong Hwi Jeong, Young Kyung Lim, Se Byeong Lee, Dongho Shin Proton Therpy Center, Ntionl Cncer Center, Goyng, Kore Received 9 Novemer 217 Revised 13 Decemer 217 Accepted 19 Decemer 217 Corresponding uthor Dongho Shin (dongho@ncc.re.kr) Tel: Fx: When high density metllic implnt is plced in the pth of the proton em, sptil heterogeneity cn e cused due to rtifcts in three dimensionl (3D) computed tomogrphy (CT) scns. These rtifcts result in rnge uncertinty in dose clcultion in tretment plnning system (). And this uncertinty my cuse significnt underdosing to the trget volume or overdosing to norml tissue eyond the trget. In clinicl cses, metl implnts must e plced in the em pth in order to preserve orgn t risk (OARs) nd increse trget coverge for tumors. So we should introduce Ti-mesh. In this pper, we mesured the lterl dose profile for proton em using n EBT3 film to confirm dosimetric impct of Ti-mesh when the Ti-mesh plte ws plced in the proton em pthwy. The effect of Ti-mesh on the proton em ws investigted y compring the lterl dose profile clculted from with the film-mesured vlue under the sme conditions. Keywords: Ti-mesh, Proton, Artifct,, EBT3 film Introduction Proton therpy hs severl dvntges over conventionl rdition therpies using clinicl liner ccelertor (CLINAC). For exmple, the distl fll-off in depth dose distriution nd high-energy deposition in the Brgg pek re ssure little irrdition dmge on norml tissues except for the tumor. Although proton therpy mkes it possile to concentrte the dose on tumor, there exist vrious uncertinties in proton tretments; setup uncertinties, ptient motion uncertinties, rnge uncertinties relted to tissue heterogeneities. 1) Especilly, if high density metllic implnt is plced in the pth of the proton em, sptil heterogeneity cn e cused due to rtifcts in three dimensionl (3D) computed tomogrphy (CT) scns. These rtifcts result in rnge uncertinty in dose clcultion in tretment plnning system (), s cusing fewer signls to the detector nd much imge loss to which X-ry is sored more in the high density mteril region thn in the norml region during the CT scn. 2,3) Eventully, this uncertinty my cuse significnt underdosing to the trget volume or overdosing to norml tissue eyond the trget. 4) Therefore, during ctul ptient tretment, it is recommended to void plcing metl implnts in the proton em pth. However, in clinicl cses, metl implnts must e plced in the em pth in order to preserve orgn t risk (OARs) nd increse trget coverge for tumors. So we should introduce Ti-mesh. Titnium mesh implnts re cliniclly ppeling s they re strong, light-weight, foldle nd mgneticlly nd iologiclly comptile. In ddition, Ti-mesh hs een studied in severl groups to show much less rtifct on CT scn thn other high-density metllic implnts. ) In this pper, we mesured the lterl dose profile for Copyright 217 Koren Society of Medicl Physics CC This is n Open-Access rticle distriuted under the terms of the Cretive Commons Attriution Non-Commercil License ( which permits unrestricted non-commercil use, distriution, nd reproduction in ny medium, provided the originl work is properly cited.

2 Progress in Medicl Physics Vol. 28, No. 4, Decemer proton em using n EBT3 film to confirm dosimetric impct of Ti-mesh when the Ti-mesh plte ws plced in the proton em pthwy. The effect of Ti-mesh on the proton em ws investigted y compring the lterl dose profile clculted from with the film-mesured vlue under the sme conditions. Experimentl Methods y 2%. 6,7) As solute dose nlysis with the results clculted y is impossile, so we should mke reltive comprison nlysis. The films were scnned using n Epson Expression 1 XL scnner (Epson Americ Inc, Long Bech, CA, USA) nd nlyzed with RIT113 ver..2 Lterl dose profiles for proton em re mesured using EBT3 film in solid wter phntom (3 cm 3 cm 2 ) to study dosimetric impct of Ti-mesh on proton em therpy. The proton em fcility used in the present work ws the Ion Bem Applictions (IBA, Louvin-L-Neuve, Belgium) cyclotron PROTEUS 23, locted t the Ntionl Cncer Center of Kore. The em energy ws 16 MeV doule-scttering (DS) proton em with rnge (R) of 8.9 cm nd spred out rgg pek (SOBP) of.33 cm. As shown in Fig. 1, Ti-mesh with.6 mm thick nd cm 2 re ws plced t depth cm phntom nd films were respectively rrnged t depths of,, 1, nd 3 mm sed on the mesh. A 2 cgy DS proton em ws irrdited y chnging the gntry ngle to, 3 nd deg. To compre the difference of dose profile with nd without Ti-mesh, the proton em ws irrdited under the sme conditions without loding the Ti-mesh. When proton em is irrdited on n EBT3 film, quenching effect occurs t the Brgg pek, nd the output tends to decrese mm mm 1 mm 3 mm Fig. 2. () Phntom study on the effects of Ti-mesh on DS proton dose in ; () lterl dose profiles depending on depth clculted y proton convolution lgorithm in. 16 MeV, proton em Gntry ngle:, 3, degree Ti mesh.6 mm thick, 1.1x9.8 cm 2 EBT3 film,, 1, 3 mm cm Ti mesh Solid wter phntom 1 cm Fig. 1. The schemtic of experiment setup for lterl profile mesurements.

3 146 Shinheng Cho, et l:dosimetric Impct of Ti Mesh on Proton Bem Therpy softwre USA). Results The Phntom Study in System A phntom system, which ws set up to mesure the lterl dose profile of the film, ws scnned y our CT scnner nd the CT imges were imported into the Eclipse (Vrin Medicl System Inc.) system. As shown in Fig. 2, the proton em under sme conditions ws plced to the phntom imported to the system. CT ws scnned on n extended scle t 2 mm slice thickness using Siemens Senstion Open CT scnner (Siemens Medicl Solutions USA, Inc., Mlvern, PA, USA). In cse of norml CT, the CT HU numer is etween - nd +2, ut s the CT HU vlue is much lrger for high density mterils, it need to scn to n extended scle so tht entire imge cn e seen. And since our CT scnner cn e scnned with the IMAR version, the CT reconstruction lgorithm is pplied to the defult vlue to improve the imge qulity y correcting the CT rtifct cused y the mesh. Using the proton convolution superposition (Eclipse version 1) lgorithm, the lterl dose profiles were clculted with 1 mm grid size. The proton convolution superposition lgorithm inputs the chrcteristics of the ctul mesured proton em into em dt t of system nd clculte the dose y mking mthemticl em modeling using virtul source, sed on the dt. Fig. 2 shows lterl dose profiles depending on depth clculted y proton convolution lgorithm in. The profiles ccording to depth show similr ptterns t,, nd 1 mm nd dose reduction t 3 mm. The dose perturtion seen in the grph is considered to e the result of the effect of the ptterned mesh structure when the proton em psses through the Ti-mesh plte. The dose reduction phenomenon oserved t 3 mm is descried in the SOBP curve of Fig. 3. Fig. 3 shows the SOBP curve of doule scttering proton em with energy of 16 MeV. As shown in Fig. 2, the portion corresponding to depth 3 mm from the Ti-mesh is mtched with the end of the rnge in the SOBP curve of Fig. 3 nd the reltive dose of this prt indictes 9%. Fig. 3 shows grph of lterl dose profiles long the depth direction of the film t gntry ngle of degrees. As shown in Fig. 3, it cn e seen tht dose perturtion occurs in the mesh section in lmost the sme mnner s in. The irregulr shpe of the is due to scttering y the mesh structure, so tht the perturtion is more irregulr depending on the depth. At 3 mm depth, dose reduction phenomenon occurs s well s, which is exctly the dose profile result in. When we mesure other high-density mterils such s Au mrkers, which re not ctul mesh, in the em pth, they lso tend to hve similr dose distriution over depth. When the distnce etween the mesh nd the trget is completely close, the effect is lmost not exhiited. If the intervl is more thn t constnt, the phenomenon such Energy: 16 MeV SOBP:.33 cm Rnge: 8.9 cm mm mm 1 mm 3 mm Gntry degree Fig. 3. () SOBP curve in 16 MeV DS proton em; () lterl film dose profile mesured depending on depth t gntry ngle degree.

4 Progress in Medicl Physics Vol. 28, No. 4, Decemer s scttering ppers well. Fig. 4 is grph showing the difference in Dose distriution with nd without Ti-mesh. The dt showed the lrgest effect of dose perturtion t depth 1cm from mesh plte in ctul film mesurement. So it ws compred sed on depth 1cm. The verge reltive dose ws.31% nd the stndrd devition ws.32 when the mesh ws present. The men reltive vlue ws.12% nd the stndrd devition ws.11 when there ws no mesh. Therefore, it ws confirmed tht Dose perturtion phenomenon clerly ppers when Timesh is plced. Fig. is grph compring the lterl dose profile clculted y nd the film mesured long with gntry ngle t depth of 1 cm. As shown in the grph, lthough there is reltive difference in the numer of With mesh w/o mesh Gntry degree Depth: 1cm Fig. 4. Lterl dose profile t the middle of the SOBP with nd without the mesh plte t depth 1 cm in film mesurement. perturtion oscilltions due to the scttering effect long the em direction, it ws confirmed tht the overll dose distriution nd virtion type mtch ech other. Discussion nd Summry In this study, we investigted the dosimetric effect of Ti-mesh on the proton em y mesuring the lterl dose profile of the DS proton em using EBT3 film nd compring the result with the clculted vlue in. Previous studies hve reported tht when high-density metl implnts re used in rdition therpy, underdosing or overdosing on tumors in dose clcultion t cn e cused due to rnge uncertinty y rtifcts during CT scns. And Ti-mesh lso hs een studied to show much less rtifct in CT scn thn conventionl photon studies. Therefore, we should need to confirm how ccurte the dose clculted y when using proton therpy with Ti-mesh in ctul tretment, nd compred with the mesured lterl dose profile using film. Our experimentl results showed no dose reduction in the Ti-mesh region nd showed dose profile very similr to tht of. Of course, in the cse of films, the solute dose cn t e compred, so we cn t mke quntittive comprison with the results. In order to mke more quntittive comprison, we try to compre the exct rnge error y mesuring the percentge depth dose (PDD) for proton em. As it is difficult to mesure the PDD with film, we re currently fricting system for c Gntry degree Gntry 3 degree Gntry degree Fig.. Comprtive nlysis etween dose profiles of film nd depending on gntry ngle t depth 1 cm.

5 148 Shinheng Cho, et l:dosimetric Impct of Ti Mesh on Proton Bem Therpy mesuring the PDD using n ion chmer y plcing Timesh on 3D wter phntom. We will lso hve study on the dosimetric impct of Ti-mesh through comprison for results of three methods such s, chmer mesurement nd theoreticl clcultion through Monte Crlo simultion. This study is preliminry experiment for further study, nd we think tht Ti-mesh showed the possiility of clinicl ppliction in proton therpy. Acknowledgements This work ws supported y the Ntionl Nucler R&D Progrm through the Ntionl Reserch Foundtion of Kore (NRF), funded y the Ministry of Eduction, Science nd Technology (NRF-217R1D1A1B3316). Conflicts of Interest The uthors hve nothing to disclose. Avilility of Dt nd Mterils All relevnt dt re within the pper nd its Supporting Informtion files. References 1. Ming Yng, X Ronld Zhu, Peter C Prk. Comprehensive nlysis of proton rnge uncertinties relted to ptient stopping-power-rtio estimtion using the stoichiometric clirtion. Physics in Medicine nd Biology 212; 7: Kssim I, Joosten H, Brnhoorn JC, Heijmen BJ, Dirkx ML. Implictions of rtifcts reduction in the plnning CT originted from the implnted fiducil mrkers. Medicl Dosimetry 211; 36(2): Yzdi M, Gingrs L, Beulieu L. An dptive pproch to metl rtifct reduction in helicl computed tomogrphy for rdition therpy tretment plnning: experimentl nd clinicl studies. Interntionl Journl of Rdition Oncology*Biology*Physics 2; 62(4): H Lin, X Ding, L Yin, H Zhi. The effects of titnium mesh on pssive-scttering proton dose. Physics in Medicine nd Biology 214; 9:N81 N89.. Ptone H, Brker J, Roerge D. Effects of neurosurgicl titnium mesh on rdition dose. Medicl Dosimetry 26; 31: Reinhrdt S, Hillrnd M, Wilkens J, Assmnn W. Comprison of Gfchromic EBT2 nd EBT3 films for clinicl photon nd proton ems. Medicl Physics 212; 39: SW Kng, JB Chung. Evlution of dul-chnnel compound method for EBT3 film dosimetry. Progress in Medicl Physics 217; 28(1): Hertnto A, Zhng QH, Hu YC, Dzyuk O, Rimmer A, Mgers G. Reduction of irregulr Brething rtifcts in respirtion-correlted CT imges using respirtory motion model. Medicl Physics 212; 39: