Room: Track 3
Purpose: We propose an approach to measure linear energy transfer (LET) spectra and lateral dose profiles for characterization of therapeutic proton beams in air and water. The proposed experimental method can be applied to acquire data needed for commissioning and validation of Monte Carlo (MC) based treatment planning system (TPS) and are essential for treatment planning using radiobiological models with variable RBE.
Methods: A commercial semiconductor silicon pixel detector TimePix (TPX) was used for measurements of energy depositions and track lengths of single primary and secondary particles produced by proton pencil beams at 100, 150 and 200 MeV in air and water. We designed a thin and waterproof PMMA holder, which was used for positioning of the detector inside a water phantom. Following the calibration and dose profile measurements in air, we acquired about 360 LET spectra at different positions in water phantom. The LET spectra as well as LET and dose profiles were compared to GATE/Geant4 MC simulations of the experimental setup.
Results: We found that in air (i) TPX calibration measurements of LET spectra are well in agreement with simulations and (ii) TPX lateral dose profile measurements are in good agreement with facility commissioning data. We summarize the comparison of TPX measurements and MC simulations in water for lateral dose profiles, lateral and longitudinal LET profiles, and LET spectra. The preliminary comparison of LET spectra obtained from experimental results to MC simulations show moderate differences.
Conclusion: A thorough characterization of proton pencil beam in air and water is feasible using commercial detector, water phantom and in-house designed waterproof holder. The proposed approach can be implemented at any proton therapy facility to acquire experimental data to commission and validate MC-based TPS and LET component of RBE-weighted biological dose computations.
Funding Support, Disclosures, and Conflict of Interest: This project is carried out within the Reintegration programme of the Foundation for Polish Science co-financed by the EU under the European Regional Development Fund -- grant no. POIR.04.04.00-00-2475/16-00. This research was supported in part by computing resources of ACC Cyfronet AGH.