ESTRO 2025 - Abstract Book

S2849

Physics - Dose prediction, optimisation and applications of photon and electron planning

ESTRO 2025

References: Springer A, et al. Total body irradiation with volumetric modulated arc therapy: Dosimetric data and first clinical experience. Radiation Oncology (2016) 11:46. Wong JYC, et al. Total body irradiation: guidelines from the International Lymphoma Radiation Oncology Group (ILROG). Int J Radiat Oncol Biol Phys 2018; 101: 521-529. Mancosu P, et al. Total marrow irradiation for hematopoietic malignancies using volumetric modulated arc therapy: a review of treatment planning studies. Phys Imaging Radiat Oncol 2019; 11: 47-53. Litoborska J, et al. Evaluation of three VMAT-TMI planning methods to find an appropriate balance between plan complexity and the resulting dose distribution. Phys Medica 2020; 75: 26-32.

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Digital Poster Dosimetric comparison of inverse optimization versus forward optimization in MRI-guided high-dose-rate brachytherapy of cervical cancer Manuel Cruz-Gonzalez 1 , Francisco Pino-Sorroche 1 , Dina Najjari 2 , Ruth Gracia 1 , Cristina Gullón 1 , Francisco Camba 1 , Llorenç Benaches Magraner 1 , Cristina Picón 1 1 Department of Medical Physics, Institut Català d'Oncologia, L'Hospitalet de Llobregat, Spain. 2 Department of Radiation Oncology, Institut Català d'Oncologia, L'Hospitalet de Llobregat, Spain Purpose/Objective: To compare inverse optimization using the HIPO algorithm with forward optimization (FO) in MRI-guided high-dose rate intracavitary and interstitial brachytherapy for cervical cancer, focusing on dosimetric parameters. Material/Methods: Forward-optimized plans for MRI-guided high-dose-rate intracavitary and interstitial brachytherapy of cervical cancer (N=17) were retrospectively re-optimized using the HIPO (Hybrid Inverse Planning Optimization) algorithm. Dose-volume constraints for the HIPO optimization were empirically derived from a case involving six needles. During re-optimization, the active dwell positions from the forward optimization (FO) were preserved, along with the dwell times for the ovoids and intrauterine applicator. The inverse planning algorithm was applied to specifically adjust the needle dwell times. The mean number of needles used was six (range: 4–10). Dosimetric parameters from forward and inverse optimizations were statistically compared using the Wilcoxon signed-rank test. Results: Optimization with the HIPO algorithm resulted in a higher dose to the GTV and CTV_HR compared to forward optimization (FO). The D98 for GTV_res was 133% and 124% of the prescribed dose for HIPO and FO plans, respectively (p=0.312). Similarly, the D90 for CTV_HR was 115% versus 108% (p=0.591), and the D98 for CTV_HR was 98% versus 90% for HIPO and FO plans (p=0.005). For CTV_IR, the D90 was 69% versus 66% (p=0.659), and the D98 was 56% versus 52% for HIPO and FO plans (p=0.648). HIPO maintained a similar dose at the recto-vaginal point, delivering 42% and 41% of the prescribed dose for HIPO and FO, respectively (p=0.115). The conformity of the plans improved with HIPO, with a COIN of 0.38 compared to 0.36 for FO (p=0.159). However, the ratio of needle dwell time to total dwell time and Dose Nonuniformity Ratio (DNR) remained consistent between the two optimizations, at 0.19 (p=0.015) and 0.61 (p=0.023), respectively.