S1858
Physics - Dose prediction/calculation, optimisation and applications for photon and electron planning
ESTRO 2026
References: Akyol, O., Dirican, B., Toklu, T., Eren, H., & Olgar, T. (2019). Investigating the effect of dental implant materials with different densities on radiotherapy dose distribution using Monte-Carlo simulation and pencil beam convolution algorithm. Dentomaxillofacial Radiology, 48(4), 20180267.Greco, T. G. L., & Vu, K. (2024). Dosimetric significance of manual density overrides in oropharyngeal cancer. Medical Dosimetry, 49(3), 198-205.Le Fèvre, C., Brinkert, D., Menoux, I., Kuntz, F., Antoni, D., El Bitar, Z., Thiery, A., Fabbro, O., & Noël, G. (2020). Effects of a metallic implant on radiotherapy planning treatment— experience on a human cadaver. Chinese clinical oncology, 9(2), 14. Keywords: Metallic implants, planning, manual override Optimizing HyperArc™ Beam-Angle Selection for Intracranial Lesions: A Weighted Evaluation of Normal Brain Sparing and PTV Dosimetry Jaruek Kanphet, Jumnong Kumkhwao, Warocha Saenkla, Metinee Wisetrintong Radiation Oncology, King Chulalongkorn Memorial Hospital, Bangkok, Thailand Purpose/Objective: To determine the most advantageous beam-angle configuration for HyperArc™ planning for 4 cm3 intracranial lesions at five anatomical locations: Front- Right (FR), Front-Left (FL), Back-Right (BR), Back-Left (BL), and Central (C). The investigation was driven by a weighted scoring approach, deliberately prioritizing Normal Brain sparing (40%), PTV diametric quality (50%), and treatment efficiency (10%). Material/Methods: A total of 48 non-coplanar single-fraction SRT plans were generated in Varian Eclipse using the HyperArc™ module. Five predefined arc configurations were used: R1 (Beam Angle = 180.1° CW 0.0° Collimator = 60°Couch = 0°, R2 (Beam Angle = 0° CCW 180.1°,45°, 315°), M (Beam Angle = 179.9°CCW 0°, 75°, 90°), L1 (Beam Angle = 0° CW 179.9°, 45°,45°), and L2 (Beam Angle = 179.9° CCW 0°, 60°, 0°). The planning process employed the same template objectives and Digital Poster 1830 optimization stop criteria across all 48 plans. Eleven essential diametric and efficiency metrics, including PTV dose (Min/Max/Mean dose, CI, HI), Normal Brain dose (Max/Mean, V30cc, V80cc), and MU, were collected. Data was normalized and subsequently synthesized into a weighted composite score Results: The optimal beam angles were unequivocally shown to be location-dependent. The 3Arc_R1-R2-L1 plan
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Dose difference in standard plan, plan without density override and plan with extended CT scale when there is metallic implant in cranial radiotherapy Hoi Ying Choi Radiotherapy, HKSH, Hong Kong, Hong Kong Purpose/Objective: RT plays an essential role in the management of brain cancers. However, approximately 4% of cancer patients who undergo RT have metallic implants. These implants are composed of high Z atomic number materials which may affect the dose calculation in RT planning. Thus, this study aims to investigate the dose impact of metallic implant on brain cancer radiotherapy planning when using manual density override plan, without density override plan and extended CT scale plan, so as to determine the necessity of manual intervention for dose accuracy. Material/Methods: 15 brain cancer patients with metallic implants in cranial region were recruited. Metallic implants and artifacts were delineated. All the implants composed of titanium alloy. The mass density of screw were 4.34g/cm3 and the assigned relative electron density were 3.72. Standard VMAT plan with manual density override was optimized. All three plans were then recalculated by MIM SureCal. Dose parameters including Dmax, Dmean, Dmin, D95, coverage, HI and CI for target were collected. Dmax and Dmean for OAR were recorded. Gamma analysis was performed for all three plans. Friedman Test, Wilcoxon Signed Ranks Test and Post hoc test with Bonferroni correction were conducted to determine the significance of dose difference among three plans. Results: Statistical analysis revealed no significant differences in target doses, coverage, or critical organ doses across the three planning approaches. Gamma analysis was all exceeded 95% in most case, except one case only achieved 94.38% in extended CT scale plan. Conclusion: Current practice of manual contouring of metallic implants and artifacts is a labor-intensive, time- consuming, and resource dependent process. In this study, no significant dose difference were reported in both target and OAR in all three plans. The possible reasons may the size, location, components of the implants. Larger scale of study is needed to further investigate the dose impact of metallic implant, and whether manual density override is a necessary in all metallic implant cases.
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