ESTRO 2024 - Abstract Book

S3252

Physics - Detectors, dose measurement and phantoms

ESTRO 2024

1265

Digital Poster

Comparison of total out-of-field dose in 6 MV VMAT and proton therapy for classical Hodgkin lymphoma

Mona Azizi 1,2 , Maite Romero-Expósito 3,2 , Ignacio López-Martínez 4 , Isidora Muñoz 4 , Ignacio Espinoza 4 , Ola Norrlid 5 , Christina Goldkuhl 6 , Daniel Molin 7 , Beatriz Sánchez-Nieto 4 , Iuliana Toma-Dasu 1,2 , Alexandru Dasu 3,7 1 Stockholm University, Physics, Stockholm, Sweden. 2 Karolinska Institute, Oncology Pathology Department, Stockholm, Sweden. 3 The Skandion Clinic, ., Uppsala, Sweden. 4 Pontificia Universidad Católica de Chile, Instituto de Física, santiago, Chile. 5 Uppsala University Hospital, Department of Immunology, Genetics and Pathology, Uppsala, Sweden. 6 Sahlgrenska University Hospital, Department of Oncology, Gothenburg, Sweden. 7 Uppsala University, Department of Immunology, Genetics and Pathology, Uppsala, Sweden

Purpose/Objective:

Personalized dosimetry has a crucial role in both photon and proton therapy. It traditionally concerns the individualization of the plan to maximize tumor effect and to minimize dose to healthy tissues to reduce the risk of long-term side effects. However, effective curative treatment and long-expected survival has highlighted the need to account for dose outside the target volume in addition to therapeutic doses. The main purpose of this study is therefore, to evaluate the dose to healthy tissue from photon therapy with 6 MV Volumetric Modulated Arc Therapy (VMAT) and compare it to out-of-field equivalent dose from neutrons and protons in proton therapy for classical Hodgkin lymphoma (cHL) patients.

Material/Methods:

cHL patients from photon and proton therapy cohorts of the PRO-Hodgkin study have been included in the study. A proton and a photon plan were created for each patient and the planning CT was used to generate a synthetic whole body CT image with the help of the IS 2 aR software [1]. For the photon cohort, the total out-of-field organ doses were determined within the whole-body phantom using the dose distribution provided by the treatment planning system (TPS) and the Periphocal 3D (P3D) software [2]. This assessment required using the prescribed dose, monitor units, field size, and location of the isocenter in each of the original photon plans. For proton therapy patients, the total out-of-field dose was calculated as the sum of proton, neutron and photon dose. Proton absorbed doses were calculated from the TPS and then multiplied by a relative biological effectiveness (RBE) factor equal to 1.1. Neutron and photon equivalent doses were computed through the Monte Carlo simulation of the proton plan, using the MCNP 6.2 code [3]. This is the most detailed individualized dose determination of out of-field doses in photon and proton therapy.

The mean out-of-field doses in low-dose regions were calculated for specified organs at risk, including the lungs, thyroid, spinal cord, esophagus, and prostate and reported relative to the prescribed dose to the target. The study is