ESTRO 2024 - Abstract Book

S3311

Physics - Detectors, dose measurement and phantoms

ESTRO 2024

Individual organ dose calculations from CT imaging of Hodgkin lymphoma patients treated with protons

Angeliki Gkavonatsiou 1,2 , Mona Azizi 2,3 , Maite Romero Expósito 1,3 , Christina Goldkuhl 4 , Daniel Molin 5 , Karin Andersson 1,5 , Alexandru Dasu 1,5 1 The Skandion Clinic, The Skandion Clinic, Uppsala, Sweden. 2 Stockholm University, Medical Radiation Physics, Stockholm, Sweden. 3 Karolinska Institutet, Oncology Pathology Department, Stockhom, Sweden. 4 Sahlgrenska University Hospital, Department of Oncology, Gothenburg, Sweden. 5 Uppsala University, Department of Immunology, Genetics and Pathology, Uppsala, Sweden

Purpose/Objective:

Proton therapy (PT) patients may undergo many computed tomography (CT) imaging sessions during the course of treatment both for treatment planning purposes as well as for verifying the positioning and anatomy. Given that patients may live for many years after their treatment, the contribution of CT imaging to the overall radiation doses is of interest from the perspective of the risk of inducing second malignancies after treatment. Therefore, the objective of this study was to investigate the individual CT imaging organ doses of patients treated with PT for classical Hodgkin lymphoma (cHL). The study is a part of the SINFONIA project on the risk appraisal for detrimental effects of radiation exposure during the management of cancer patients.

Material/Methods:

A cohort of 38 patients included in the PRO Hodgkin study and treated in the Skandion clinic between 2019 and 2023 was studied with respect to doses from CT planning and verification scans. Individual organ doses were calculated from parameters extracted from the DICOM tags of CT images of each patient. Various imaging protocols could be used depending on the type of treatment the patient receives. Thus, patients treated in free breathing (FB) are often imaged in FB with 4DCT added to investigate the breathing amplitude. In contrast, patients treated in Deep Inspiration Breath Hold (DIBH) are imaged in DIBH (with the same CT protocol as standard FB scans), while at least two scans with Low Dose (LD) protocols are used to investigate the repeatability of the breath hold. Therefore, the first step was to sort the CT images according to protocol. Then, the VirtualDose software (1) was used to calculate organ doses using individually extracted scan parameters for each scan. Then, for each patient, doses from individual CT scans were summed to determine the total organ dose received during the treatment course. To our knowledge, this is the first systematic analysis of imaging doses in patients receiving proton therapy. The results showed a significant variation in the number of total CT scans as well as the protocols used between the patients. In particular, the average and median number of CT scans during the proton treatment were 7.6 and 9.0 respectively, with a range between 3 and 12 scans. Figure 1 presents the distribution of doses to various organs in male and female patients. The large variations are due in part to the variation in the number of scans between patients and in part to the extension of the scanning volume as it includes some of the reported organs or part of them in some cases and not in others. The only notable exception was the gonads that were not inside the irradiated area in any of the cases. The organs that are more distant from the treatment region such as the brain, colon, and gonads received the lowest dose. In male patients, the liver and stomach had higher doses among the reported organs while in female patients, the lungs and heart received the larger doses. Figure 2 displays the same trend as Results: