Feasibility study of utilizing XRV-124 scintillation detector for quality assurance of spot profile in pencil beam scanning proton therapy.

Purpose: The purpose of the current study is to (i) investigate the feasibility of utilizing the XRV-124 - a cone-shaped scintillation detector - to measure the spot size and spot position in pencil beam scanning proton therapy, and (ii) compare the spot sizes acquired by the XRV-124 with that of the widely used Lynx detector.

Methods: Spot position was tested by delivering a map of 30 spots at different locations to the XRV-124. Spot position test included energies 70-210 MeV. Spot size measurements were performed at the isocenter using the XRV-124 and Lynx detectors for a total of 32 energies (70-225 MeV at an increment of 5 MeV) at four cardinal gantry angles.

Results: The position (X, Y, and Z) of the radiation isocenter was within ±0.3 mm. For spots placed on the horizontal (X) and longitudinal (Y) axes of the spot map, both the X and Y locations of the spots were within ±0.5 mm. The spots placed diagonally in the map showed a higher deviation (±0.9 mm). In evaluating spot sizes acquired using the XRV-124 vs. Lynx, the results from the XRV were found to be slightly higher but within 0.2 mm for energies ≥130 MeV and within 0.4 mm for energies <130 MeV.

Conclusions: It is feasible to utilize the XRV-124 to perform the quality assurance of position and size of a pencil proton beam around the radiation isocenter but within the usable XRV-124 cone area.