Room: Exhibit Hall | Forum 4
Purpose: Modern radiotherapy challenges encompass the quality assurance of complex dynamically varying beams delivered to moving and deforming patients anatomy. Hence, there is a growing need for a real-time 3D deformable detector. This work aims at characterizing the response of a discretely deformed volumetric scintillation dosimeter.
Methods: Discrete deformation states were embodied using three plastic scintillators (EJ-260) having different dimensions, one cube and two cylinders (r=1cm, r=1.5cm), but of essentially the same volume (27cm3). The scintillators were successively immersed in a filled acrylic tank (12x12x15cm) and irradiated with parallel opposed beams (6MV). To assess the impact of refractive index mismatches, the acrylic tank was filled with distilled water (n=1.33), propylene glycol (n=1.43) or glycerin (n=1.46). The scintillation light was collected with a polychromatic CCD camera (Alta U2000) placed on the treatment couch and Cerenkov was decoupled using the hyperspectral formalism.
Results: Curved surfaces converged more scintillation photons towards the camera than planar surfaces. The relative differences, corrected for dose, between the cumulative light collected from the cube and the curved surface of both cylinders decreased from 13Â±2% and 10Â±1% to 6Â±1% when immersed respectively in water, propylene glycol, and glycerin. Nonetheless, akin geometries, that is curved and planar surfaces, yielded similar signals despite deformations of more than 1 cm. Indeed, they respectively presented deviations of 1.0% and 2.8% (water), 0.4% and 2.7% (propylene glycol), and 0.8% and 0.1% (glycerin).
Conclusion: This work targets the challenges of a real-time volumetric deformable scintillation detector. The cumulative light collected from the different geometries presents variations arising not only from the dose deposited but mostly from refraction. Those variations can be significantly reduced by minimizing the refractive index mismatch between the scintillator and its surrounding medium. Otherwise, these effects are reproducible and thus could be accounted for in the 3D reconstruction process.
Funding Support, Disclosures, and Conflict of Interest: This work was financed by the Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery grants #435510-2013 and #2018-04055. Emily Cloutier acknowledges support by the Fonds de Recherche du Quebec Nature et Technologies (FRQNT) and partial support by the NSERC CREATE Medical Physics Research Training Network grant (#432290).