Verification of dose distribution on the gamma knife perfexion radiosurgery using gafchromic EBT3 film: RANDO phantom study

Leksell gamma knife (LGK) is an advanced modality of radiation therapy sourced Co-60 radioactive for treating patient with intracranial lesion. Small field techniques with highly integrated radiation delivering to patients in single session must be calculated accurately and verified carefully. This study illustrates a procedure to verify the accuracy of dose distribution associated with Leksell Gamma Plan (LGP) using RANDO phantom and gafchromic EBT3 film dosimetry. First, we assessed the profile dose on LGK standard phantom with collimators size 4, 8 and 16 mm and compared the results with the profile dose based on RANDO to obtained Full Width Half Maximum (FWHM) and beam-symmetry. Absorbed-dose distributions on RANDO with various combinations of lesion volume, collimator size, location and number of shots assessed by EBT3 film using LGK Perfexion. Scanned images of the measured films were processed following standard EBT3 film-handling procedures. Dose distribution calculation were performed using ImageJ software and MATLAB in-house software. The study shows different FHWM and beam symmetry of collimator size of 16 mm on standard phantom between LGP and measurement is 1.83 % and 1.58 % respectively whereas the discrepancy in RANDO phantom is 2.15 %, and 1.64 % respectively. Verification of max dose shows the smallest discrepancy on collimator size 16 single shot is 1.9 % on 7.61 cc superior lesion volume, where 12.12 Gy obtained by measurement and 12.36 Gy from LGP. In conclusion, collimator size 16 mm have a highest accuracy of FWHM and beam-symmetry value. However, on smaller lesion volume, collimator 16 mm with single shot give higher deviation dose value.