ESTRO 2024 - Abstract Book

S3222

Physics - Detectors, dose measurement and phantoms

ESTRO 2024

878

Digital Poster

Integrating imaging doses in RT dosimetry for secondary cancer risk assessment.

Maite Romero-Expósito 1,2 , Beatriz Sánchez-Nieto 3 , Mercedes Riveira-Martin 4 , Jessica Hernández-Sánchez 3 , Gabriel Zelada 5 , Mona Azizi 6,2 , Antonio López-Medina 7 , Iuliana Toma-Dasu 6,2 , Alexandru Dasu 1,8 1 Skandion Clinic, ., Uppsala, Sweden. 2 Karolinska Institutet, Oncology Pathology Department, Uppsala, Sweden. 3 Pontificia Universidad Católica de Chile, Instituto de Física, Santiago, Chile. 4 Galicia Sur Health Research Institute, Medical Physics and RP Department, Vigo, Spain. 5 Clínica Alemana-Universidad del Desarrollo, Servicio de Radioterapia, Santiago, Chile. 6 Stockholm University, Medical Radiation Physics, Stockholm, Sweden. 7 University Hospital of Vigo, Meixoeiro Hospital, Medical Physics and RP Department (GALARIA), Vigo, Spain. 8 Department of Immunology, Genetics and Pathology, Uppsala University, Medical Radiation Sciences, Uppsala, Sweden

Purpose/Objective:

Radiotherapy (RT) treatments are increasingly improving survival of cancer patients, increasing in turn the need for evaluating long-terms effects, such as the induction of second cancers (SC), especially for young patients. SC risk assessment relies on accurate determination of the total dose received by the patient due to both the treatment and the imaging procedures. This work aims to introduce a methodology to include imaging dose in the assessment of the SC risk associated with RT based on thermoluminescent dosimeters (TLDs) measurements and Monte Carlo (MC) simulations. The study was carried out within the EU-funded SINFONIA project on the risk appraisal for detrimental effects of radiation exposure during the management of cancer patients.

Material/Methods:

TLDs measurements of photon absorbed dose were carried out in an anthropomorphic phantom (ATOM 701-D) receiving a VMAT prostate treatment fraction, as well as a pelvis planning CT scan and one CBCT scan. Irradiations were carried out with an Elekta Synergy linac, a Siemens Somatom Definition AS+ scanner and an Elekta XVI system, respectively. A total of 217 dosimeters were inserted within the 39 slices of the phantom. As organ doses are defined by the dose to a few points, only an approximate dose distribution can be obtained. A MC simulation on the voxelized phantom, mimicking a Hodgkin lymphoma patient, provided a more detailed dose distribution corresponding to a chest CBCT with the same Elekta XVI system. Dose-volume histograms (DVHs) for different binnings and mean doses were obtained and compared.

Results:

The TLD absorbed doses in the anthropomorphic phantom showed a comparable pattern for both imaging procedures: two plateau regions separated by a transition region (Figure 1). The first plateau is beyond the scanned volume with an average dose of 0.103 and 0.212 mGy for CT and CBCT, respectively. The second plateau is within the scanned volume, with an average dose of 10.5 mGy for CT and 18.1 mGy for CBCT. On average, for the case measured, the CBCT delivers 1.7 times the CT dose. Approximate differential DVHs built using the TLD measurements for organs