ESTRO 2025 - Abstract Book

S2888

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

ESTRO 2025

3677

Digital Poster Comprehensive assessment of imaging and out-of-field doses in Hodgkin Lymphoma: implications for secondary cancer risk in VMAT and proton therapy Mona Aziz 1,2 , Maite Romero-Expósito 3,2 , Isidora Muñoz 3 , Ignacio N.López-Martínez 4 , Ignacio Espinoza 4 , Ola Norrlid 5 , Christina Goldkuhl 6 , Daniel Molin 7 , Beatriz Sánchez-Nieto 4 , Iuliana Toma-Dasu 1,2 , Alexandru Dasu 3,5 1 Medical Radiation Physics, Stockholm University, Stockholm, Sweden. 2 Oncology and Patology, Karolinska Institute, Stockholm, Sweden. 3 Medical Physics, Skandion Clinic, Uppsala, Sweden. 4 Pontificia Universidad Católica de Chile, Instituto de Física, Santiago, Chile. 5 Department of Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden. 6 Department of Oncology, Sahlgrenska University Hospital, Gothenburg, Sweden. 7 Experimental and Clinical Oncology, Department of Immunology, Genetics and Pathology, Uppsala University, Uppsalal, Sweden Purpose/Objective: Radiation therapy is an effective treatment for Hodgkin lymphoma (HL) but is associated with late adverse effects from the irradiation of organs-at-risk (OARs). Furthermore, image guidance for setup and treatment verification contributes with additional radiation exposure. This study presents a comparative assessment of out-of-field and imaging doses from proton therapy (PT) and VMAT contributing to the secondary cancer risks in a HL cohort. Material/Methods: A comprehensive framework was developed to integrate imaging and out-of-field doses with in-field doses, enabling individualized determination of total organ doses. The framework has been applied for the systematic assessment of the total radiation dose delivered to HL patients receiving PT or VMAT treatments. For each patient, planning CT data were used to generate synthetic whole-body CT images with the IS2aR MATLAB-based software [1]. For the VMAT treatment course, in-field doses were obtained from the treatment planning system, while out-of-field photon doses were calculated using the Periphocal 3D software [2]. For PT, the total dose was computed as the sum of the proton RBE-weighted dose from the TPS and the photon and neutron equivalent doses calculated using the MCNP 6.2 code. Imaging doses from kV-CBCT imaging were simulated with GATE (v9.2), while doses from planning and verification CT scans were determined using the VirtualDose software [3]. Finally, the lifetime attributable risk (LAR) was calculated for each patient for both modalities. Results: Our results show that imaging doses represent a significant contribution to out-of-field doses in radiation therapy. Variability in imaging protocols led to heterogeneous dose increases in both modalities, especially in PT. Depending on the protocol, imaging can raise the total dose for distant OARs by over 10% relative to treatment doses in VMAT and by more than 100% in PT, however for lower absolute doses. In terms of risk assessment, considering the total dose resulted in higher LAR values. LAR estimates were generally higher for VMAT than PT, indicating the risk minimizing potential for the latter technique; for instance, after accounting for the total dose, lung LAR increased from approximately 14% to 19% in VMAT and from 7.5% to 9% in PT in one patient case. Conclusion: Radiation burden in high-precision radiotherapy, including out-of-field treatment and imaging doses, should be taken into account for epidemiological studies, as well as for plan optimization to reduce the incidence of secondary cancers in future patient cohorts.

Keywords: Proton therapy, Cone-beam CT, VMAT

References: [1]

I. S. Muñoz-Hernández et al., Phys. Medica, 2023. B. Sánchez-Nieto, et al., Front. Oncol., 2022.

[2] [3]

A. Ding et al., Phys Med Biol; 2015.