S1817
Physics - Dose prediction/calculation, optimisation and applications for photon and electron planning
ESTRO 2026
and clinical benefits of modern SRS optimisation techniques in reducing the predicted toxicity for brain metastases. References: References:[1] Milano MT. Grimm J. Niemierko A. Soltys SG. Moiseenko V. Redmond KJ. et al. Single- and Multifraction Stereotactic Radiosurgery Dose/Volume Tolerances of the Brain. International Journal of Radiation Oncology*Biology*Physics 2021;110:68– 86. https://doi.org/10.1016/j.ijrobp.2020.08.013.[2] Paoletti L. Ceccarelli C. Menichelli C. Aristei C. Borghesi S. Tucci E. et al. Special stereotactic radiotherapy techniques: procedures and equipment for treatment simulation and dose delivery. Rep Pract Oncol Radiother 2022;27:1– 9. https://doi.org/10.5603/RPOR.a2021.0129. Keywords: Brain metastases, NTCP, SRS Development and validation of a 3D printing– based bolus optimization system for electron conformal therapy Sang-Won Kang 1 , Jin-Beom Chung 1 , Moo-Jae Han 1 , Jae- Sung Kim 1,2 1 Radiation Oncology, Seoul National University Bundang Hospital, Seongnam, Korea, Republic of. 2 Radiation Oncology, Seoul National University College of Medicine, Seoul, Korea, Republic of Purpose/Objective: This study aimed to develop and evaluate a fast electron dose calculation engine and an optimization algorithm to implement a 3D printing–based bolus optimization system for electron conformal therapy (ECT). Material/Methods: Dose optimization was performed using a Digital Poster 1078 backtracking line search method applied to the tumor contour corresponding to the prescribed dose line. The developed electron dose calculation engine (EDCE), based on a modified Hogstrom algorithm, was validated against the Monte Carlo–based electron dose calculation algorithm (eMC) implemented in the Eclipse treatment planning system (TPS). Comparisons of percentage depth dose (PDD) and lateral profiles were performed, and gamma analysis was conducted with 3%/3 mm criteria. Subsequently, a 3D-printed silicone bolus was fabricated according to the optimized design, and dose verification was performed using solid water and anthropomorphic phantoms with EBT3 film measurements. Results: For 6 MeV electrons, EDCE showed good agreement with eMC, with a PDD RMSE of 2.07 and lateral profile RMSEs of 3.10–1.54 at depths of 11–27 mm. The
volume were not correlated (p=0.33). Increased number of targets (p=0.003), coplanar field geometry (p<0.0001), and non-SRS-optimised VMAT (p<0.0001) were associated with higher NTCP and larger Brain- GTV/CTV V18Gy (Table 1). The NTCP difference between single- and multi-target plans was also evident within the SRS-optimised group (Figure 1a), while SRS optimisation markedly reduced NTCP across all volumes (Figure 1b).
Conclusion: In this cohort of 473 SRS treatments, technical advancements—particularly dedicated SRS optimisation and non-coplanar geometries— significantly reduced the irradiated brain volume and consequently the estimated risk of oedema and radionecrosis. These findings highlight the dosimetric
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