Patient-specific quality control for stereotactic cranial radiosurgery

Abstract

Patient-specific quality control (PSQC) has been carried out for 25 cranial radiosurgery plans delivered using a TrueBeam STx (Varian, Palo Alto, CA) equipped with an ExacTrac (BrainLab, Munich, Germany) imaging system. The StereoTactic End-to-End Verification (STEEV) phantom (CIRS Inc., Norfolk, VA) was used to measure both point doses using a microDiamond detector (PTW, Freiburg, Germany) and 2D dose planes using gafchromic type EBT-XD film (Ashland, NJ, USA). The Octavius 4D and 1000SRS array (PTW, Freiburg, Germany) was used to measure 3D dose distributions. Point doses were recorded using the planned couch positions and then with the couch angle reset to zero degrees to remove the influence of directional dependence of the microDiamond. The mean difference between measured and calculated point doses was −3.2 ± 1.1% using planned couch positions and −1.8 ± 0.9% with the influence of couch angle removed. The mean difference in the point dose measured using the Octavius was −1.1 ± 0.7% and the mean gamma pass rate for 2%/1 mm criteria (10% threshold) was 99.4 ± 0.7%. The mean pass rate using 5%/1 mm global gamma criteria for the film analysis was 97.1 ± 3.4% with only 1 result below 90%. The mean pass rate using 3%/2 mm local gamma (10% threshold) was 82.3 ± 12.5% with 5 results less than 70% however all these consisted of plans with average equivalent square field sizes of