ESTRO 2024 - Abstract Book

S3327

Physics - Detectors, dose measurement and phantoms

ESTRO 2024

4. Gómez F, Gonzalez-Castaño DM, Fernández NG, Pardo-Montero J, Schüller A, Gasparini A, et al. Development of an ultra-thin parallel plate ionization chamber for dosimetry in FLASH radiotherapy. Med Phys. 2022;49:4705–14.

2299

Mini-Oral

LET characterization in proton beams using different (micro-) dosimetry detectors

Ana Vaniqui, Marijke De Saint-Hubert, Olivier van Hoey, Lara Struelens

SCK CEN, RDA, Mol, Belgium

Purpose/Objective:

Intensity modulated proton therapy (IMPT) can promote low integral doses and high conformity. The higher radiobiological effectiveness (RBE) of protons, with respect to photons, is clinically accounted by a constant factor. Experimental evidence shows that RBE is in fact variable, depends on multiple biophysical parameters and neglecting its variation can lead to the underestimation of normal tissue complication. RBE presents a monotonic relationship with linear energy transfer (LET), a computable and measureable quantity that can combine different beam qualities contributing to damage in a single value. Thus, the LET-RBE dependence can be explored as a predictor for biological damage. For understanding this relationship, precise LET characterization along with biophysical simulations are necessary. In this work, we have explored the use of different solid-state based (micro-) dosimetry detectors for LET characterization.

Material/Methods:

The detectors MiniPIX-Timepix and Microplus were used in facilities with beams of protons and carbon ions for measuring and deriving LET. The former is a high-sensitivity hybrid semiconductor that provides spectrometric information of charged particles in mixed radiation fields and allows single-particle tracking with high-spatial resolution and spectral response. The latter is a microdosimetry probe composed by a PMMA sheath and a silicon on-insulator microdosimeter, with sensitive volumes mimicking the dimensions of a cell array. The detectors were irradiated at representative positions along pristine and spread-out Brag peaks. Different simulations for dose, LET and lineal energy were developed and compared against the experimental data.

Results:

Both proton and carbon measurements showed a significant increase in LET from the entrance region towards the distal edge, as expected. Figure 1 shows that for monoenergetic proton beams of 149 MeV and 160 MeV, increasing mean (fluence-averaged) LET values of 1.9 keV/μm (entrance) and 4.3 keV/μm (R95), 5.8 keV/μm (R75) keV/μm were measured, in accordance with values obtained from passive detectors and simulations. For a spread-out Bragg peak the same trend was observed, with LET values ranging from 0.9 keV/μm (entrance), 1.4 keV/μm (middle), 3.3