Room: Karl Dean Ballroom B1
Purpose: To test feasibility of MR compatible Metal Oxide Field Effect Transistors (MOSFETs) for MRI-Linac in-vivo patient dosimetry under 0.345 T magnetic field
Methods: With the advent of MRI Linac systems it is desirable to have online (wireless), MR compatible in-vivo dosimeters. The real-time MOSFET dosimeters, TN-502RDH10 with long leads and developed by Best Medical Canada, were studied to evaluate their MR compatibility and dosimetry properties. MOSFETs were calibrated with 6 MV flattening filter free (FFF) beam on Varian TrueBeamTM Linac at Dmax. Measurements were performed to test MOSFET response under 0.345T low field strength from ViewRay MRIdian LinacTM. Measurements were performed with and without the magnetic field turn on. The long lead detectors allowed the wireless reader to be placed outside the 5 Gauss low field line. TLDs were also irradiated under similar conditions as a secondary dosimetry check. DQA test for a clinical plan was also performed.
Results: The response of the MR compatible MOSFETs with long leads (3.25 m) was linear and not affected by the magnetic field, for different MU settings (100 to 600 MU) and field size of 9.96x9.96 cm2. The readings were consistent with TLD measurements. DQA results also showed agreement (Â±4%) compared to the ion chamber readings
Conclusion: This study demonstrates that MR compatible MOSFETs with long leads can be used for real-time in-vivo dose verification for 0.345T MRI-Linac system. The MOSFET system permits effective and independent validation of complex treatment plans.