ESTRO 2024 - Abstract Book

S3329

Physics - Detectors, dose measurement and phantoms

ESTRO 2024

role. Coupling the detector response and simulations with biophysical models is ongoing and will be validated against the in-vitro DNA damage results. Microdosimetry has a potential to provide confidence in particle therapy delivery considering LET and RBE optimization. Moreover, when we consider that highly modulated fields may result in inhomogeneous LET distributions, quality assurance in clinical particle therapy may require the development of (micro-) dosimetry verification along with physical dose.

Keywords: LET, Proton therapy, Dosimetry

2316

Digital Poster

Energy correction factors for out of field dosimetry with radiophotoluminescent dosimeters

Meïssane M'hamdi 1 , Pauline Maury 1 , Mesut Aydin 2 , Marc-André Boivin 2 , Nathan Benzazon 1 , Eric Deutsch 1 , Charlotte Robert 1 , Ibrahima Diallo 1

1 Gustave Roussy, UMR1030, Villejuif, France. 2 Gustave Roussy, Radiation Oncology, Villejuif, France

Purpose/Objective:

In external beam radiotherapy (EBRT), doses are inevitably deposited outside the treatment field. These low doses impact the probability of radiation induced toxicities such as second cancer, cardiac toxicities or lymphopenia [1,2]. In the era of the combination of radiotherapy and immunotherapy, out-of-field dosimetry appears to be a crucial topic for the optimization of treatment plans. In particular, the mechanisms by which EBRT may induce radio-induced lymphopenia (RIL) are not known, but one hypothesis could be the non negligible distant doses received by the lymphoid organs. Several studies showed that modern treatment planning software underestimate the doses outside the treatment field [3,4]. In order to have a better understanding of the mechanism of RIL, being able to accurately evaluate doses outside the treatment field is a decisive step to achieve. Radiophotoluminescent glass dosimeters (RPLGD) present interesting properties for the determination of the out-of field doses thanks to their low detection limit (30 µGy). Their small size allows an easy placement on patient’s skin which is helpful for dose measurements at specific organs. Nevertheless, out-of-field measurement present challenges, as the energy spectrum outside of the treatment field is softer [5]. RPLGD are energy-dependent detectors and the changes in the spectrum will impact the dose response. In order to have accurate dose measurement, those variations must be corrected. The aim of this work was to define energy correction factors, k en , usable for the out-of field dosimetry.

Material/Methods:

The AGC Techno Glass Corporation system (RPLGD & FGD-1000 readout system) was investigated. Dosimeters are silver-doped phosphate glasses with a diameter of 1.5 mm and a length of 12 mm. The uniformity and reproducibility of response to irradiation were tested on 500 detectors. Two models were used in this study: GD-302M (N = 154) and GD-352M (N = 135). For the first one, the glass rod is inserted in a plastic holder of 2.8 mm diameter and 13 mm length. For the second one, in addition to the plastic holder, a 0.75 mm thick filter is present (90% Sn, 10% Pb).