Evaluation of a two-dimensional diode array for patient-specific quality assurance of HyperArc

Purpose To evaluate a two-dimensional diode array for patient-specific quality assurance of VMAT stereotactic radiosurgery (SRS) plans. Methods The diode array, an SRS MapCHECK (SRSMC), was composed of a 77 mm x77 mm face-centered array having a spacing of 2.47 mm. Sixty SRS plans were selected from our clinical database, 30 for treatment of a single target and 30 for multiple targets. The target sizes ranged from 2.4 mm to 44.7 mm equivalent diameter (median 8.7 mm). The plans were delivered to the diode array. For multiple target plans, two measurements were obtained at two locations, one corresponding to the largest target and the other to the smallest target. Gamma using a 3%/1 mm criteria and the dose to the center diode were compared with radiochromic film (RCF). Dose to selected regions of the detector electronics was calculated. Results The mean difference between the center diode and RCF was -1.2%. For a threshold of at least 95% of detectors/pixels having gamma < 1 for a 3%/1 mm criteria, SRSMC and RCF gave consistent results for 79 of the 90 measurements. For plans with an arc having a patient support angle of 90 degrees or 270 degrees, the median dose to the electronics was 0.65% of the prescription dose. Conclusions SRSMC is an efficient tool for accurate patient-specific quality assurance of VMAT single and multiple target radiosurgery, yielding similar clinical decisions as radiochromic film.