ESTRO 2023 - Abstract Book

S1505

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ESTRO 2023

Conclusion This study found that the interplay effect had a statistically significant adverse dosimetric impact for 10MV FFF ungated SBRT due to the high DRmax 2400MU/min. This adverse impact on ADD could be decreased by using a target dose with reduced dose inhomogeneity due to the significant correlation found between ADD and dose CV of ITVacv. On the other hand, the stop-and-go effect showed no significant effect on the ADD. To conclude, the interplay effect outweighed the stop-and-go effect for the TrueBeam linear accelerator.

PO-1783 Framework for out-of-field dosimetry in photon radiotherapy: application to Hodgkin lymphoma

M. Romero-Expósito 1 , M. Romero-Expósito 2 , I. Muñoz 3 , I. López-Martínez 3 , I. Espinoza 3 , I. Toma-Dasu 4,5 , A. Dasu 1,6 , D. Molin 7 , B. Sánchez-Nieto 3 1 The Skandion Clinic, -, Uppsala, Sweden; 2 Karolinska Institutet, Oncology Pathology Department , Stockholm, Sweden; 3 Pontificia Universidad Católica de Chile, Instituto de Física, Santiago, Chile; 4 Karolinska Institutet, Oncology Pathology Department, Stockholm, Sweden; 5 Stockholm University, Medical Radiation Physics, Stockholm, Sweden; 6 Uppsala University, Medical Radiation Sciences, Department of Immunology, Genetics and Pathology, Uppsala, Sweden; 7 Uppsala University, Experimental and Clinical Oncology, Department of Immunology, Genetics and Pathology, Uppsala, Sweden Purpose or Objective The improved outcome of radiotherapy (RT) treatments raises the awareness of long terms effects, such as secondary cancers. This is of special interest for young patients, treated with a curative intent, a group where classical Hodgkin lymphoma (cHL) is common. The objective of this work is to present the implementation of a framework for cHL patients to evaluate the out-of-field doses related to secondary cancer risk. Materials and Methods The system consists of 2 integrated Matlab-based programs to process the dicom files of a RT plan exported from the TPS. The first program, IS ² aR ( Rad. Oncol. 2022;170:S1341-S1342 ), generates a virtual whole-body CT phantom using the original CT of the patient, which covers only a small volume of the patient around the target, as an input. This program registers the patient CT with the reference phantoms from ICRP-110. The second program, Periphocal 3D (P3D), has implemented the analytical model by Sánchez-Nieto et al ( Front. Oncol. 2022;12:872752 ) to evaluate peripheral photon dose in the virtual phantom from the number of MU, the prescription dose, the mean field (from 50% isodose) and the out-of-field area (defined from the 5% isodose). With all these inputs, P3D calculates the DVHs of the organs delineated on the ICRP-110 that falls in the out-of-field area. The system was tested in cHL patients, treated with VMAT.