S804 I. J. Radiation Oncology d Biology d Physics Volume 78, Number 3, Supplement, 2010

and that of a proton gantry, two questions arise: (1) is it practical to expect the same accuracy in gantry isocentricity for PT? (2)What is the dosimetric effect with degradation in isocentricity? We attempt to answer these two questions in this study.

Materials/Methods: Several star shots are taken in one of our gantry rooms (TR3) with a 1cm aperture to examine its variation with:(1) different snouts, (2) different energies, and (2) different snout positions: retracted and extended. The star shots are analyzed withImageJ and RIT to check the consistency of analysis. Degradation in isocentricity may be manifested as a change in the x-, y- and z-coordinate of the isocenter, resulting in deviation in dose delivery from plan. To investigate the dosimetric effect, several treatmentsites are studied: pancreas, prostate, spinal AVM, and head-and-neck. The isocenter position in the x-, y- and z-directions is changedsystematically in the range: 0.5-2.8 mm to simulate the different extents of isocentricity degradation. Dose calculation is performedon an Eclipse planning system. For each site, DVH of PTV and the organs at risks (OAR) are compared for the different plans.

Results: The gantry isocentricity from star shots taken during acceptance and in subsequent annual calibrations are: 0.95, 1.0, 1.0 from2007-2009 for the first gantry room, and 1.6 and 2.0 mm for the second gantry room (TR3) in 2008 and 2009 respectively. The star shots inTR3 are about 2.3 mm with the 10cm-3 snout irrespective of the snout position or energy. When mounted, 10cm-3 appeared to have a verytiny room of play. The star shot taken with another 10 cm snout, 10cm-2, yields 1.9 mm. The mounting of 10cm-2 was snugged. A com-parison of the DVH of the PTV and OAR for the pancreas plans shows that the coverage of PTV remains relatively constant even fora change of isocentricity of 2 mm. However, the V50(liver) decreases by 14% or increase by 10%, depending on the direction of degra-dation, V50(stomach) exhibits a ±40% change , while the V50 for both small bowel and duodenum change by +3% and -6% respectively.

Conclusions: The star shots are independent of snout position and energy. However, due to the sheer weight of a proton gantry, thesnout must be fitted snuggly to the nozzle. Any displacement of the snout, no matter how small, will translate into a misalignment inthe star shot since it is the closest component to the film. The flex and sag of the gantry as it rotates due to its enormous weight maybe another factor to cause the star shot to deviate from tolerance and may lead to dose delivery deviations from plan.

Author Disclosure: C. Cheng, None; C. Allgower, None; B. Hawkins, None; L. McHugh, None; V. Derenchuk, None; I. Das, None.

3342 Improving Clinical Potential, Efficiency and Robustness of Planning and Delivery of IMPT for

Skull-based Chordomas

X. Zhang1, R. X. Zhang1, L. Dong1, Y. Li1, A. Trofimov2, T. F. Delaney2, A. Mahajan1, R. Mohan1

1M. D. Anderson Cancer Center, Houston, TX, 2Massachusetts General, Hospital, Boston, MA

Purpose/Objective(s): To explore techniques to improve clinical potential (quality), efficiency and robustness of IMPT and toassess the potential of IMPT vs. IMRT for base of skull chordomas.

Materials/Methods: The IMPT and IMRT plans were designed for each of 5 skull-based chordoma cases. CTV to PTV margin of3 mm was used and dose prescription was 74 Gy (RBE) to $95% PTV. Larger number (e.g., . 4) of IMPT beams improve quality,but considerably increase CPU time for optimization. Furthermore, the number of energy layers required for each beam for targetsat shallow depths can be very large (?60) and can lead to very long beam-on times (?2 sec per layer in our case). Higher energybeams with energy absorbers to widen the Bragg peak and, thus, reduce the number of energy layers were used. To reduce thenumber of beams per treatment session, 8 or 9-beam plans were divided into multiple plans of 3 to 4 beams each delivered on se-quential days. Each plan is optimized independently. The summed plans were assessed and compared for quality, efficiency androbustness with the plans using the same set of smaller or large number beams treated daily. Robustness was assessed using the‘‘worst case analysis’’ (WCA) (Lomax et. Al, Z. Med Phys., 14, 147-52). In it, 8 dose distributions were calculated after shiftingthe CT image by ±3 mm along x, y and x directions and by changing the range by +/- 3%. Worst case dose in each voxel for thetarget is represented by the minimum of any of the plans and for each normal structure of interest by the maximum. The confor-mality index (CI), heterogeneity index (HI) and dose volume indices were used to compare dose distributions.

Results: Averaged over 5 patients, sparing of normal structure was superior for IMPT vs. IMRT: Brain V30 4.1% (3.4%-5.9%) vs.7.1%(4.7%-9.8%); brainstem V67 2.0%(0.0%-6.3%) vs. 5.4%(0.8%-14.8%); optic chiasm V60 6.5%(0.0%- 32.3%) vs. 8.8%(0.0%-43.9%); temporal lobes V65 and 2.4% (0.0%-8.0%) vs. 3.8% (0.0%-10.4%) respectively. The IMPT plans were more con-formal (CI = 1.24 (1.16-1.34)) but more heterogeneous (HI = 0.086(0.079-0.097) than IMRT plans (CI = 1.31 (1.22-1.44), HI =0.036 (0.028-0.045)). So far robustness analysis has been completed for three cases and shows that 96.7% (95.3-99.4%) CTV re-ceived 100% of prescribed dose in the worst case scenario and the minimum dose to the CTV was 72.5 Gy (71.7-74Gy). Normaltissue doses increased but were still within tolerance. Both the planning and delivery times were reduced by approximately a factorof 2 with the use of energy absorber.

Conclusions: Preliminary data suggest that the IMPT plans for base of skull chordomas designed based on the proposed strategyare robust and superior compared to IMRT plans. Use of energy absorbers improves planning and delivery efficiency. (Supportedby NCI P01CA021239.)

Author Disclosure: X. Zhang, None; R.X. Zhang, None; L. Dong, None; Y. Li, None; A. Trofimov, None; T.F. Delaney, None; A.Mahajan, None; R. Mohan, None.

3343 Accelerating Monte Carlo Simulation for Radiotherapy Dose Calculation using a Massively Parallel

Graphics Processing Unit

Y. Zhuge, H. Xie, R. W. Miller

NIH, Bethesda, MD

Purpose/Objective(s): The Monte Carlo (MC) simulation for radiotherapy dose calculation is a computationally intensive task.Typically, many days are required to simulate the transport of photons/electrons for a regular patient CT data, which has limited itsuse in clinical practices. Graphic Processor Units (GPUs) have recently demonstrated substantial parallel computing power to ac-celerate scientific computing applications. The purpose of this study is to speed up the MCDOSE code, a well-known MC simu-lation for photon/electron radiation dose calculation, by using GPU on a regular desktop PC, and to test the clinically usefulness ofthe GPU MC code addition to the radiation treatment planning process.

Materials/Methods: We developed our GPU MC code that has similar features as the MCDOSE by using a new massively data-parallel, C-based CUDA programming language API for NVIDIA graphic boards. The GPU MC code can both simulate the transportof photons and electrons in a 3D rectilinear phantom geometry. The voxels in the phantom can have uniform or variable dimensions

Proceedings of the 52nd Annual ASTRO Meeting S805

and the material in the voxel can be specified by the user or determined from the electron density data derived from the patient CTdata. Source models are supported in the GPU MC code. The simulation was executed in an NVIDIA Tesla C1060 computing pro-cessor, a GPU specially designed for high performance computing which contains 240 streaming processor cores at 1.3GHz and4GByte of memory. We use 60 blocks and each of them has 256 threads so in total one grid has 15360 threads. Each thread processesone particle history for photon/electron energy reduction and dose deposition, so there are 15360 particle histories being parallel cal-culated with one time kernel function call. Kernel function is executed in a serial way until all particle histories are processed.

Results: We tested our GPU MC code on patient CT data with image size of 512 x 512 x 124 and voxel size of 1.0 mm x 1.0 mm x3.0 mm, by simulating 15MV, and 6MV photon beams, each involving 2x10e7, 2x10e8 particles (respectively). The depth dosecurves produced from our program showed a very good agreement with those from the MCDOSE. But for efficiency, the GPU MCcode achieved around 8-fold speedup over the CPU simulation.

Conclusions: This study shows that MC simulation for radiotherapy dose calculation is very suitable to be implemented by usingCUDA interface for NVIDIA GPUs on a regular desktop PC. The simulation computational performance can be significantly speedup by this new technique.

Author Disclosure: Y. Zhuge, None; H. Xie, None; R.W. Miller, None.

3344 How Did the Particle Therapy Grow in the Japanese Radiation Therapy Field? Current Status of Proton

and Carbon Ion Radiotherapy from 2002 to 2009 in Japan

Y. Ando1, T. Kamada1, N. Fuwa2, H. Sakurai3, T. Ogino4, S. Murayama5, K. Yamamoto6, Y. Hishikawa7, M. Murakami7,

T. Nakano8

1National Institute of Radiological Sciences, Chiba 263-8555, Japan, 2Southern Tohoku Proton Therapy Center, Koriyama 963-8563, Japan, 3Proton Medical Research Center, University of Tsukuba, Tsukuba, Ibaragi 305-8575, Japan, 4Division ofRadiation Oncology, National Cancer Center, Kashiwa, Chiba 277-8577, Japan, 5Proton Therapy Division, Shizuoka CancerCenter Hospital, Shizuoka 411-8777, Japan, 6The Wakasa Wan Energy Research Center, Tsuruga, Fukui 914-0192, Japan,7Hyogo Ion Beam Medical center, Tatsuno, Hyogo 679-5165, Japan, 8Graduate School of Medicine, Gunma University,Maebashi, Gunma 371-8511, Japan

Purpose/Objective(s): In Japan, we have experienced the particle therapy for more than ten years. The Japan Clinical Study Groupof Particle Therapy (JCPT) studied the achievements of the Japanese particle therapy from 2002 to 2009. Our study group coveredthe all Japanese particle therapy institutions. The aim of the paper is to disclose the status of the Japanese particle therapy and toanalyze the change of the number of the therapy.

Materials/Methods: The JCPT member consisted of the eight particle therapy institutions. Each hospital was (1) Southern TohokuProton Therapy Center, (2) Proton Medical Research Center, University of Tsukuba, (3) Division of Radiation Oncology, NationalCancer Center, (4) Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, (5) Proton TherapyDivision, Shizuoka Cancer Center Hospital, (6) The Wakasa Wan Energy Research Center, (7) Hyogo Ion Beam Medical centerand (8) Gunma University. The JCPT office gathered each institution’s annual report and analyzed the number of treatments. Par-ticle therapy was divided into a proton therapy and a carbon ion therapy. We analyzed the disease, gender and age distributions.

Results: The number of particle therapy treatment from 2002 to 2009 reached 10,782. Each annual number of particle therapy was520 (244 proton: p, 276 carbon: c) in 2002, 794 (474 p, 320 c) in 2003, 1082 (699 p, 383 c) in 2004, 1276 (803 p, 473 c) in 2005,1453 (827 p, 626 c) in 2006, 1712 (923 p, 789 c) in 2007, 1712 (781 p, 931 c) in 2008, 2233 (1278 p, 955 c) in 2009. The number ofpatients according to the primary lesion ranged 198 (164 p, 34 c) for CNS tumors, 1448 (815 p, 633 c) for Head and Neck tumors,1241 (742 p, 499 c) for lung tumors, 112 (77 p, 35 c) for upper digestive organ tumors, 1257 (947 p, 310 c) for liver tumors, 151 (42p, 109 c) for pancreas tumors, 73 (8 p, 65 c) for gynecological tumors, 2509 (1770 p, 739 c) for prostate tumors, 659 (118 p, 541 c)for bone and soft tissue tumors, 246 (44 p, 202 c) for recurrent rectal tumors and 1275 (438 p, 837 c) for other or unclassified tu-mors. The treatment for prostate cancer was a major target. The gender distribution of the patients treated by the particle therapy was7933 for male and 2849 for female. The male patients were almost three times as many as the female patients.

Conclusions: This paper reports the activity of Japanese particle therapy for 8 years. We think that the analysis of the particle ther-apy is very important for the radiation oncology. We will be able to realize the desirable co-operation between the JCPT hospitalsand establish the Japanese database concerned with the proton and carbon ion therapy.This study was supported by Grants-in-Aid for Scientific Research (2009-Gan Ippan-008) from the Ministry of Health, Labor andWelfare of Japan.

Author Disclosure: Y. Ando, None; T. Kamada, None; N. Fuwa, None; H. Sakurai, None; T. Ogino, None; S. Murayama, None; K.Yamamoto, None; Y. Hishikawa, None; M. Murakami, None; T. Nakano, None.

3345 Uncertainty and Margin Study for IMRT, VMAT, and Proton Beam Therapy for Treatment after

Radical Prostatectomy

Y. Cui1, A. S. Harrison1, M. T. Studenski1, T. N. Showalter1, J. O. Deasy2, Y. Yu1, J. M. Galvin1, Y. Xiao1

1Thomas Jefferson University Hospital, Philadelphia, PA, 2Washington University, Saint Louis, MO

Purpose/Objective(s): To compare the uncertainties of 3D dose distributions, caused by the geometrical uncertainty of patientsetup, in IMRT, VMAT, and proton plans for post-prostatectomy treatment. To test the effectiveness of a common margin recipein these three types of treatment plans.

Materials/Methods: Four prostate fossa patient datasets were included. For each case three different plans were carried out: anIMRT plan of nine fields (XiO, Elekta), a VMAT plan, and a proton plan with two lateral active scanning beams (Oncentra, Nu-cletron). The plan robustness analysis function in CERR (Washington University, St. Louis, MO) software was used to simulate theDVH uncertainty with given systematic (S) and random (s) shifts in three dimensions. Five different combinations of S (2-4 mm)and s (2-4 mm) representing clinical situations were used for all plans. The DVH uncertainty range (upper and lower bounds) wasgenerated by CERR for each setting of S and s with a certain confidence level (95% was used in this study). We tested CTV cov-erage using a common margin recipe (2.5 S + 0.7 s) for all IMRT, VMAT, and proton plans.