Purpose: This study introduces a novel hybrid detector capable of simultaneous dose and direct irradiation angle measurements based on Cerenkov angular dependency.
Methods: A Cerenkov probe composed of a 10-mm long sensitive volume of clear PMMA fiber separated by an absorptive filter from a 1-mm diameter transport fiber was built. Filtered and raw Cerenkov signals respectively from the sensitive volume and the transport fiber were collected using the Hyperscint RP-200 scintillation dosimetry platform (Medscint, Quebec, QC). An independent scintillation probe composed of 10-mm BCF12 scintillating fiber (Saint-Gobain, Hiram, OH) was also used for simultaneous dose measurements. Dose calibration of each detector signal was accomplished with repeated irradiations of 200 cGy (6 and 18 MV) and the total signal was deconvolved using a hyperspectral approach. Using a solid-water phantom, measurements at fixed incident angles covering a wide range of doses, dose rates as well as output factors were realized. A cylindrical phantom was then used to obtain an angular calibration curve for fixed dose irradiations and perform irradiation angle measurements.
Results: For fixed incident angle, signal characterization of the Cerenkov detector displays a linear dose-light relationship for the whole range of doses and dose rates tested. The sensitive volume signal shows a discrepancy with the predicted dose that reaches 1.1 % for the lowest dose rate. Output factors were accurately measured within ±0.8 % for field size up to 25x25 cm². Irradiation angle measurements using various doses exhibit an absolute mean error of 1.86° and 1.02° at 6 and 18 MV, respectively.
Conclusion: The ability to measure both irradiation angle and dose from a clinical photon beam using novel hybrid scintillation-Cerenkov detector was shown. These results offer promising perspectives for future applications in external beam radiotherapy, especially for stereotactic radiosurgery (SRS) and magnetic resonance image-guided radiotherapy (MR-IGRT).
Funding Support, Disclosures, and Conflict of Interest: This work was supported by the Natural Sciences and Engineering Research Council of Canada (NSERC) and the Fellowships Program of the Ministere de la Sante et des Services Sociaux du Quebec (MSSS). Francois Therriault-Proulx and Simon Lambert-Girard are Co-founder at Medscint inc. This work was not financially supported by Medscint.