Poster — Thur Eve — 30: Plastic Scintillation Detector Characterization for Small Fields and Stereotactic Radiosurgery Quality Assurance

Abstract

Purpose: To compare the performance of a plastic scintillation detector (PSD) for quality assurance (QA) in stereotactic radiosurgery to micro‐chamber (MC), gafchromic films, shielded diode (SD) and unshielded diodes (UD). Method and Materials: The PSD consists of a 1 mm diameter by 1 mm long scintillating fiber coupled to a polymethyl‐methacrylate optical fiber. Output factors and dose profiles for apertures used in radiosurgery have been measured. Moreover, a typical stereotactic radiosurgery treatment, using four non‐coplanar arcs, was delivered on a spherical phantom in which UD, MC or PSD was placed at the isocenter, where 15 Gy was prescribed. Results: The output factors measured with the PSD are within a mean discrepancy of 1 % compared to UD for the small apertures when normalized to the 35 mm cone. For larger cones the PSD is within 1.3% compared to the SD and the MC. When done with a 35 mm cone, the measured dose for an entire typical stereotactic plan by the PSD is within 1.8% of the measurement performed using the MC and within 1% of the planning system. Volume averaging of the MC can be observed for the 5 mm aperture, where the PSD measurement differs by as much as 9.1%. Conclusion: For stereotactic radiosurgery treatment verification, the PSD gives accurate results compared to the MC once the output factor ratio are taken into account to correct for the averaging effect of the MC. The PSD shows great potential for stereotactic radiosurgery QA measurements.