Suitability of a BeO-based OSLD system for end-to-end remote dosimetry tests in SRS/SRT applications

The aim of this study is to evaluate the suitability of a commercially available Optically Stimulated Luminescence Dosimetry (OSLD) system for remote dosimetry end-to-end tests in Stereotactic Radiosurgery and Radiotherapy (SRS/SRT). This is achieved by performing a dose-response characterization focusing on the relevant irradiation and readout conditions, followed by dosimetry protocol development and implementation.

The myOSLchip^TM Beryllium Oxide- (BeO-) based OSLD system (RadPro, Germany) was employed throughout this study. Measurements were performed to assess element sensitivity, signal depletion, linearity (up to 16 Gy), potential beam quality (6MV and 10MV) and angular dependence, signal fading rate, and potential sensitivity changes with lifetime accumulated dose (up to 98 Gy). Correction factors and uncertainties were determined following the AAPM TG-191 recommendations. The dosimetry system and protocol were implemented in an end-to-end remote dosimetry test, considering a clinically realistic single-isocenter multiple brain metastases case. For this purpose, 17 dosimeters were placed in a head phantom involving bone-mimicking inhomogeneities.

A fixed depletion correction factor may not be applicable to all OSLDs. In 6MV, a sublinear dose-response behavior (up to 5%) was observed for the dose range, reader and readout parameters investigated, while an edge-on irradiation resulted in a 2.8% under-response compared to en face. OSLD sensitivity was stable up to at least 98 Gy of accumulated dose. Overall spatial and dosimetric experimental uncertainties in the end-to-end test were estimated at 0.6 mm and 3%, respectively. The local gamma index passing rate was 100%.

The evaluated OSLD system is suitable for end-to-end tests in SRS/SRT. This study can serve as an implementation guide in such applications.