ESTRO 2024 - Abstract Book

S3193

Physics - Detectors, dose measurement and phantoms

ESTRO 2024

Figure 1: The results of the film dosimetry intercomparison for the 10Sq film grouped by each DAN. Data points represent the average dose value calculated within an ROI centered on the irradiated area of the film and normalized to the known dose. Apart from DAN_Cal, all data points were analyzed using the Host calibration film set. Error bars represent one standard deviation.

Conclusion:

This international intercomparison of film dosimetry shows that results obtained can be quite variable, even when the same software is used by different groups. Removing scanner and processing effects reduced this variability, but differences still exist, suggesting high user variability in different software solutions. This study identified that understanding the software used to process film is important in establishing an accurate film dosimetry program. The study provided the insight needed to develop a framework that can be used by radiotherapy centers to verify the quality of their film dosimetry. If results are not within tolerance, the Host and Participant can use the processes described to investigate any issues and improve the quality of the radiochromic film dosimetry.

Keywords: Film Dosimetry, intercomparison

311

Digital Poster

Dosimetry in 1.5T MR-Linacs: k B,Q correction factors for two commercially available OSL dosimeters

Vasiliki Margaroni 1 , Alexandra Drakopoulou 1 , Pantelis Karaiskos 1 , Anastasios Episkopakis 1,2 , Efi Koutsouveli 3 , Eleftherios P Pappas 1 1 National and Kapodistrian University of Athens, Medical School, Athens, Greece. 2 Elekta Ltd, Global Clinical Operations, Crawley, United Kingdom. 3 Hygeia Hospital, Medical Physics Department, Athens, Greece

Purpose/Objective:

Optically Stimulated Luminescence (OSL) dosimeters have been introduced in Quality Assurance (QA) programs for dosimetry in radiotherapy applications [1]. Due to the lack of ferromagnetic materials, OSL dosimeters may also be good candidates for QA checks in 1.5T MR-Linacs. However, due to the presence of a strong magnetic field, challenges in MR-Linac dosimetry have been identified [2]. To account for relevant changes in the detector’s dose-response, a magnetic field correction factor, k B,Q , has been introduced to complement existing codes-of-practice [2,3]. k B,Q is defined as the ratio of the detector's calibration coefficient, N B D,w to N D,w , determined with and without the presence of a magnetic field B, respectively, under beam quality Q. However, k B,Q is both detector- and orientation- specific, while data availability for OSL dosimeters is very limited. The aim of this study is to implement a Monte Carlo (MC) based framework for the determination of k B,Q values for two commercially available OSL detectors and all possible cardinal orientations with respect to the magnetic field.