ESTRO 2025 - Abstract Book

S2914

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

ESTRO 2025

Conclusion: Implementation of EMBRACE-II protocol aims improved plan conformity across international centres for patients treated with all levels of nodal involvement compared to EMBRACE-I. SIB treatment of pathological nodes using the CovP technique is feasible with high target doses and does not affect plan conformity or bowel V40Gy. This technique limits dose spillage into organs-at-risk and shows promise for application in other sites with SIB to pathological nodes or primary tumour.

Keywords: Cervix Cancer, Coverage Probability, Nodal boost

References: [1] Potter, R., et al. (2018). "The EMBRACE II study: The outcome and prospect of two decades of evolution within the GEC-ESTRO GYN working group and the EMBRACE studies." Clin Transl Radiat Oncol 9 : 48-60. [2] Ramlov, A., et al. (2017). "Clinical implementation of coverage probability planning for nodal boosting in locally advanced cervical cancer." Radiother Oncol 123 (1): 158-163. [3] Berger, T., et al. (2019). "Importance of Technique, Target Selection, Contouring, Dose Prescription, and Dose Planning in External Beam Radiation Therapy for Cervical Cancer: Evolution of Practice From EMBRACE-I to II." Int J Radiat Oncol Biol Phys 104 (4): 885-894.

3985

Digital Poster Ultra-fast Adapt-To-Shape (ATS) optimization in online MRI-guided Adaptive Radiotherapy (MRgART) for H&N and brain cancers Lanfranco Chirico 1,2 , Stefania Nici 1 , Stefano Riga 1 , Cristian Toraci 1 , Roberto G Pellegrini 3 , Edoardo Salmeri 3 , Claudia Cozzaglio 1 , Giorgio Facheris 4 , Andrea E Guerini 4 , Ludovica Pegurri 4 , Michela Buglione 4,5 , Stefano M Magrini 4,5 , Luigi Spiazzi 1 1 Medical Physics Unit, ASST Spedali Civili, Brescia, Italy. 2 Postgraduate Specialization in Medical Physics, University of Milan, Milan, Italy. 3 Elekta AB, Medical Affairs, Stockholm, Sweden. 4 Radiotherapy Department, ASST Spedali Civili, Brescia, Italy. 5 Radiation Oncology Department, University of Brescia, Brescia, Italy Purpose/Objective: There are two main options for MRgART on 1.5T Elekta Unity MR-linac (MRL): (1) applying a rigid shift to adapt to the position (ATP) of the patient; (2) re-contouring structures on the daily MRI and adapting to shape (ATS) of the current anatomy. The former workflow is very fast, but for H&N cases it might lack target coverage and produce hot spots when even small anatomical changes occur. The latter takes longer time, but allows all dosimetric criteria on targets and OARs to be achieved. The aim of this study is to test a different optimization strategy which combines the speed of ATP with the dosimetric advantages of ATS. Material/Methods: At our Institution, the usual clinical workflow for H&N and brain patients treated on MRL includes the daily online re-optimization of both fluence and weights of the offline reference plan (ATS from fluence). We selected 10 H&N cases and 8 brain cases who completed treatment on MRL to test a new time-sparing re-planning workflow: the offline plan was re-optimized only for the first fraction, while for the next ones the reference plan was chosen as the previous fraction plan. In all cases, only cost function weights, but not fluence, were re-optimized (ATS from segments). We defined this approach as ultra-fast ATS. Results: In the first analyzed 30 fractions, the average planning time following the classical ATS approach was 709s (210s to 1220s) for H&N cases and 257s (120s to 380s) for brain cases. All dosimetric constraints for target and OARs were