S1806
Physics - Dose prediction/calculation, optimisation and applications for photon and electron planning
ESTRO 2026
Thoracic Tumors. China: Shanghai Fudan University press; 2006. p. 271 - 409.2.Otto K. Volumetric modulated arc therapy: IMRT in a single gantry arc. Med Phys 2008; 35: 310–317.3.Palma D, Vollans E, James K et al. Volumetric modulated arc therapy for delivery of prostate radiotherapy: comparison with intensity-modulated radiotherapy and three- dimensional conformal radiotherapy. Int J Radiat Oncol Biol Phys 2008; 72: 996–1001.4.Sung W, Park JM, Choi CH, Ha SW, Ye SJ. The effect of photon energy on intensity-modulated radiation therapy (IMRT) plans for prostate cancer. Radiation Oncol J 2012; 30: 27–35. Keywords: oesophagus, CTRT, VMAT Proffered Paper 601 A Macro Monte Carlo approach for dose calculation of very high energy electron (VHEE) beams Chengchen Zhu 1 , Florian Amstutz 1 , Werner Volken 1 , Marco FM Stampanoni 2 , Peter Manser 1 , Michael K Fix 1 1 Division of Medical Radiation Physics and Department of Radiation Oncology, Inselspital, Bern, Switzerland. 2 Institute for Biomedical Engineering, ETH Zurich and PSI, Zurich, Switzerland Purpose/Objective: Macro Monte Carlo (MMC) methods have been used to improve dose calculation efficiency compared to general-purpose MC algorithms by modeling particle transport in large-scale macroscopic steps through the absorber. Particle parameters after each step are sampled from probability distributions determined in precalculations using local geometries and general- purpose MC. So far, MMC has been validated for electron energies up to 25 MeV and made available in the Eclipse treatment planning system [1]. This study aims to develop and validate an MMC method for very high energy electrons (VHEE) with energies up to 250 MeV. Material/Methods: Precalculations used EGSnrc [2] to simulate perpendicularly incident electrons on spheres (0.2-25 MeV) of 0.05-0.3 cm radii and slabs (25-250 MeV) of 0.2 cm thickness of water and human tissue material. Probability distributions were determined for electrons reaching the exit of the local geometry (energy loss, lateral displacement, and angular distribution) and for all particles after Møller scattering or Bremsstrahlung production (interaction location, energy, and scattering angle). The distributions were stored in a database and used for MMC transport to sample parameters after each macroscopic step. During electron macro transport, energy deposited by the electrons during each step was scored in a 3D dose grid.To validate dose calculation using MMC, we
Purpose/Objective: Chemoradiation (CTRT) is the standard treatment for locally advanced mid-oesophageal cancers (mOC)1. Studies have shown volumetric modulated arc therapy (VMAT) has superior target coverage and organ-at-risk (OAR) sparing than intensity modulation (IMRT)2,3. Also appropriate photon energy for dose calculation influences target coverage and OARs dose in other sites4. This dosimetric study investigates effect of combining different energies on VMAT planning for CTRT of mOCs in terms of target coverage and OAR dose. Material/Methods: CT simulation datasets of 35 mOC patients treated at our institution with CTRT were selected; individual dataset serving as its own control. On each dataset, VMAT plans to prescription dose of 50.4GY/28# were generated by Eclipse TPS version-15.6.06 aiming for target coverage of 95% - 107%. Control arm plan was generated with two arcs of 6MV; study arm plan with two equally weighted arcs: one each with 6 MV & 15 MV. For control plan, we performed 3 iterations; for test arm 3 iterations were done for each arc, summing 6 MV and 15 MV plans using 50% weightage of each arc to generate the test arm plan. Target coverage parameters PTV95% , CTV98% and OAR doses V5GyTotal lung V20GyTotal lung Heartmean and Spinal cordmax were compared between test and study arm plans by 2-tailed paired T test. Results: PTV95% coverage observed was >95% in both arms but difference was very highly significant (p:1.46e-11, meancontrol 96.6 SD 0.8; meantest 95.5 SD 0.4) favouring control arm. CTV98% coverage was >98% and identical in both arms (p: 0.9223; mean 99.8, SD 0.4 both arms). V5GyTotal lung difference wasn’t significant (p: 0.1541, meancontrol 91.6 SD 5.9; meantest 91.9 SD5.7), V20GyTotal lung difference was highly significant (p: 0.00006; meancontrol 17.9 SD 4.4; meantest 19.5 SD 5.8) favouring control arm. Heartmean difference was significant (p: 0.001493; meancontrol 24.1, SD 2.9; meantest 23.7 SD 3.1) favouring test arm. Spinal cord max dose difference wasn’t significant (p:0.2706; meancontrol 40.2, SD 4.4; meantest 39.7, SD 4.7). Test priori power was strong (0.8195). Conclusion: This dosimetric study on 35 CT simulation datasets by combining 6MV and 15MV arcs versus 6MV arcs alone in VMAT plans for CTRT for mOC indicates probable target coverage detriment with equivocal and variable observations in OARs (possible benefit in mean heart dose but detriment in lung dose parameters and no difference in spinal cord maximum dose). Larger well- designed studies are needed in this regard. References: 1.Hao Q, Kailiang W. Practical Radiotherapy for
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