ESTRO 2025 - Abstract Book

S2648

Physics - Detectors, dose measurement and phantoms

ESTRO 2025

dosimetrically characterized with carbon ions and a PSQA workflow was tested. The ultimate goal is to provide a user friendly and CE marked PSQA device, including software, for LIBT.

Material/Methods: Two versions of the prototype (V1 and V2) were evaluated over two years. The dosimetric tests included the evaluation of the effective measurement depth of the detector, 2D homogeneity index (2D HI) in air, cross-calibration in solid water for a 2D mono-energy scanned field (2 cm depth, 346.6 MeV/n, using ROOS type ionization chamber), dose repeatability and finally dosimetric validation (figure1-left) including reproducibility for 3D energy-modulated scanned fields (boxes). A PSQA workflow in solid water was established and measurements with V2 were compared to Treatment Planning System (TPS) dose distributions for one exemplary clinical treatment plan using global dose difference (Figure1-right).

Results: 2D HI was in satisfactory agreement with reference measurements in air using Lynx device (V1 and V2). The effective measurement depth was reduced from 18.9 (V1) to 7.5 mm (V2). Following cross-calibration, dose validation in 3D reference boxes was within +/-2%, against ROOS type chamber (Figure2). 2D repeatability was 0.6% (1-sigma for V2), 3D dose was reproduced after 13 days within 0.3% against ROOS type chamber in a reference box (V2, Figure2). Exemplary PSQA at 2 cm depth provided gamma index pass rates of 94% and 98%, considering 2%/2mm and 3%/2mm criteria, respectively (Figure1-right).

Conclusion: The new 2D array prototype V2 was found to satisfy the dosimetric requirements of LIBT and was validated for carbon ion dosimetry. A PSQA workflow was successfully tested and allowed dosimetric plan validation using commercially