Validation of Using a MapCheck3 Diode Array on SBRT PSQAs
Abstract
Purpose
MapCheck3 diode array in the MapPHAN phantom (Sun Nuclear Corporation, Melbourne, FL) appears as a reliable tool for IMRT/VMAT QAs. The objective of this work is the validation of the device for SBRT patient specific QAs (PSQA).
Methods
Seven patients treated previously with VMAT techniques were evaluated using MapCheck3. And the treatment fields were analyzed within two groups: 19 Lung SBRT fields that passed QAs using EPID and 7 SBRT fields (mixed sites) with low passing rate on EPID (e.g., due to ghosting or saturation under high-dose-rate FFF beams). The diode array was firstly calibrated in a Truebeam for 6FFF beams. Treatment plans were calculated over the QA phantom with the AAA algorithm and the RT Dose DICOM files were then imported into the SNC Patient software and compared with the measured dose distribution. Gamma test with a 10% threshold was used with evaluation criteria of 1mm distance to agreement and 3% absolute dose difference. Maximum gamma (MG), average gamma (AG), and the percentage of gamma values that are greater than 1 (PG1) were statistically analyzed between the QA results using MapCheck3 and EPID.
Results
In the first group, the average differences between Mapcheck3 and EPID on MG, AG, and PG1 were -0.58±0.29 (p=0.0003), -0.03±0.02 (p=0.2093), and -0.39%±0.95% (p=0.3627), respectively. The PSQA results from MapCheck 3 had a smaller MG but had similar AG and PG1 compared with using EPID. In the second group, MapCheck3 returned the average of MG, AG, and PG1 as 1.64±0.44, 0.31±0.06, and 3.47%±2.71%, respectively, providing 7 reasonable passing results.
Conclusion
MapCheck3 diode array in the MapPHAN is a robust tool for SBRT PSQAs. For the clinics using EPIDs as the primary PSQA device for workflow efficiency, MapCheck3 can be a great addition for verifying complex stereotactic deliveries.