ESTRO 2025 - Abstract Book

S2772

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

ESTRO 2025

Using Volumetric Modulated Arc Therapy with the Integration of Static Angle Ports and Dynamic Collimator (2024), International Journal of Radiation Oncology, Biology, Physics, Volume 120, Issue 2, S217

1568

Digital Poster Dosimetric evaluation of combining skin flash, robust optimization, and MCO methods in VMAT for patients having left-sided breast cancer Sahar Montazeri 1 , Amin Banaei 1 , Mohsen Bakhshandeh 2 , Hossein Yahyazadeh 3 1 Medical physics, Tarbiat Modares University, Tehran, Iran, Islamic Republic of. 2 Radiology Technology, Shahid Beheshti University of Medical Sciences, Tehran, Iran, Islamic Republic of. 3 Radiation Oncology, Negin Oncology Research Center, Tehran, Iran, Islamic Republic of Purpose/Objective: The purpose of this study was to evaluate and compare the dosimetric parameters of skin flash, robust optimization, and multi-criteria optimization (MCO) alone and in combination in breast cancer volumetric modulated arc therapy (VMAT) regarding the organs at risk (OARs) sparing and PTV dose coverage. Material/Methods: CT scans of 20 left-sided breast cancer patients having lumpectomy were used for VMAT treatment planning to deliver the prescribed dose (50 Gy) in Raystation (Version 8a, RaySearch Laboratories, Stockholm, Sweden). For each patient, six different plans, including conventional optimization with added skin flash (flash), MCO with skin flash considering high OARs sparing priority (Flash+MCO(O)), MCO with skin flash considering high PTV coverage priority (Flash+MCO(P)), robust optimization (robust), robust combined with MCO considering high OARs sparing (robust+MCO(O)), and robust combined with MCO considering high PTV coverage (robust+MCO(P)), were designed using two coplanar arcs. Flash thickness and robustness errors were considered equal to 1 cm in the anterior and left directions. The dosimetric objectives and constraints for MCO and conventional optimizations were used from the Craft [1] and Chan [2] studies, respectively. The dosimetric parameters related to PTV, heart, lungs, and right breast were compared between the treatment plans using SPSS (Version 26, IBM, USA).

Results:

Significant differences were found among the plans in all the dosimetric parameters ( P < 0.003) (Table 1). The robust+MCO(P) method had a significantly lower ICRU homogeneity index ( P < 0.001), and the robust+MCO(O) showed a significantly higher Paddick conformity index ( P < 0.001). The mean dose, maximum dose, V 20Gy , and V 30Gy