Room: Track 3
Purpose: Over the course of radiotherapy treatments, the anatomy of a patient may be deformed. Those anatomical variations challenge the understanding of the cumulative dose delivered. In this work, we present a novel real-time deformable dosimeter that simultaneously measures the deformation vector field and dose.
Methods: The detector prototype consists of a clear, flexible and water-equivalent cylinder elastomer in which 19 scintillating fibers (diameter: 1 mm, length: 1 cm) were inserted. The dosimeter was irradiated at 6 MV while the scintillating signal was measured using a cooled CCD camera. Dose calibration of the fibers was conducted in a 12x12x15 cm³ water tank using 15x15, 7x15 and 5x15 cm² radiation fields sizes and the validation was assessed with 8x15 and 6x15 cm² radiations fields. The resulting dose distribution measurements were compared with calculations from a treatment planning system Pinnacle 9.2 (Philips Healthcare, Andover, MA). The detector further measured the deformation vector field (DVF) through optical tracking resulting from a 1 cm antero-posterior compression. The obtained DVF was compared to the one computed by the B-Spline Plastimatch deformable image registration (DIR) algorithm.
Results: All scintillating fibers exhibited a linear dose to signal relationship at the explored doses (r² > 0.99). Once calibrated, the dose distribution from 8x15 and 6x15 cm² irradiations fields were measured and presented differences from the TPS of (mean ± std) -0.05±0.7% and 0.04±0.3% respectively. The DVF from a 1 cm compression was measured with an accuracy of 0.06 cm. A comparison with a DIR algorithm led to differences under ±1.4 and ±1.8 mm.
Conclusion: We developed and characterized a novel real-time deformable dosimeter that can accurately measure dose and deformation vector fields simultaneously. Such a detector could be used for the quality assurance of DIR and dose accumulation algorithms and to explore the dosimetric impact of organ deformations.
Funding Support, Disclosures, and Conflict of Interest: This work was supported by the Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery grants RGPIN 201905038 and 201804055. Emily Cloutier acknowledges support by the Fonds de Recherche du Quebec Nature et Technologies (FRQNT).