Verifying dynamic planning in gamma knife radiosurgery using gel dosimetry

Purpose: To assess dynamic planning based on convolution based algorithm (CABP) in Gamma Knife using gel dosimetry. Materials and Methods: PAGAT gel was prepared and filled into cylindrical container of size 8 cm in diameter for verification. An old MRI distortion phantom was modified to accommodate the gel cylinder. Advantage of this modification is that it avoids the use of metal post and pins in the vicinity of the dosimeter which causes artifacts while scanning. A X-ray CT scan was done on the phantom with cylinder positioned in the middle region. CT scanning parameters were: Tube Voltage - 120 KVp, , Tube Current - 57 mAs , Slice thickness - 1.0 mm, FOV - 265 × 265 mm2. A treatment plan was generated in Leksell Gamma Plan TPS (LGP version 10.1) using CT images of the gel phantom. Using HU values and Electron density information CABP was activated. A single shot plan with third level dynamic planning option was generated using CABPMRI with following parameters were used for scanning: CPMG sequence with 8 TE values, FOV - 256, Matrix size - 256, TR - 5000 ms, slice thickness - 1.2 mm. Results: Gamma analysis of the verification showed a pass rate of more than 83 %. This is the first kind of study for three dimensional verification of dynamic planning using convolution algorithm in Gamma Knife Perfexion. Conclusion: We propose gel dosimetry as an essential dosimeter for verifying convolution algorithm in Gamma Knife. Further experiments required to validate the verification with close agreement.