In-House Developed Dose Verification Phantom and Film Analysis Software for Gamma Knife Radiosurgery

The aim of the study was to design a simple and quick plan verification system for Gamma Knife radiosurgery (GKSRS). The latest Icon model of GKSRS includes cone beam computed tomography (CBCT) imaging. An in-house-developed phantom consists of an outer cylinder of 16-cm diameter and a circular nylon plate with threaded groove upon which an inner acrylic cylinder was fixed. This inner cylinder, further divided into two equal parts, holds EBT3 radiochromic film (Ashland Advanced Materials, NJ, United States) in the midportion for irradiation. The phantom was mounted on the Leksell stereotactic frame and set up for CBCT imaging in the treatment couch. The CBCT images were imported into the treatment planning system (TPS) for planning. A prescription dose of 2.5 Gy at the 50% isodose line was planned and a phantom with film was set in the GKSRS couch for irradiation. An in-house-developed MATLAB software (MathWorks, United States) calibrated the film, converted optical density to dose map and performed a comparison with the TPS dose. Film calibration with various doses of 0.5, 1.5, 3, and 5.5 Gy was performed with the same phantom setup as well. All films were scanned 24 hours postirradiation using an EPSON12000XL scanner at 48-bit resolution, 300 dpi, and saved as TIFF images. Gamma index analysis showed 90.5% pixel pass rate for dose difference (DD) and distance to agreement (DTA) of 3%/2-mm pass criteria. This study demonstrates a quick way to verify the TPS dose distribution during commissioning. The newly designed apparatus is an effective end-to-end test dosimetry tool for GKSRS, specifically during clinically commissioning.