This study evaluates a novel three-dimensional (3D) quality assurance (QA) device, the Mobile Phosphor Probe (MPP), for pretreatment dose verification in Gamma Knife (GK) stereotactic radiosurgery. The MPP system consists of a cylindrical phantom with a phosphor screen, an imaging unit with a charge-coupled device (CCD) camera, and a motorized driving unit. Dose distributions are reconstructed from images using a lookup table, which correlates CCD pixel optical density with dose values, calibrated against EBT3 film readings. Results show that the full width at half maximum of normalized dose distributions between film and CCD were consistent within a 0.2 mm margin. A 3D dose distribution was constructed by stacking two-dimensional images obtained at 0.3 mm intervals over a ± 30 mm range in the superior-inferior direction. Validation was achieved by comparing the reconstructed 3D doses with planned distributions across multiple planes using gamma evaluation. All cases within the 20-80% isodose line (IDL) range achieved a 95% gamma passing rate under 2.0%/2.0 mm criteria, and the 1.0%/1.0 mm criteria were met at the 50% IDL in all dimensions. The MPP system demonstrates potential as an efficient patient-specific QA tool for GK radiosurgery, offering a streamlined alternative to traditional film dosimetry.
Lee et al. (Tue,) studied this question.