Validation of Mosfet Dosimetry for In-Vivo Dose Verification In Patients with Implanted Electronic Devices
Abstract
Purpose
Recent discontinuation of OSLDs prompted the adoption of MOSFETs as an alternative for in-vivo dose verification for patients with cardiac implantable electronic devices (CIEDs). We characterized MOSFET response across clinically relevant beam delivery parameters to validate the CIED dose verification workflow.
Methods
Seventeen test plans covering multiple energies (6/15 MV FF/FFF photons, 6-18 MeV electrons), dose rates (100-1400 MU/min), SSDs (83-113 cm), and gantry angles were delivered on a Varian TrueBeam. We used a solid water-based setup to compare calibrated ion-chamber response to standard sensitivity MOSFET (TN-502RD-H, Best Medical Canada) readings. We conducted end-to-end workflow validation using an anthropomorphic phantom. The phantom was CT-simulated with a pacemaker according to local guidelines with a MOSFET placed on the phantom surface near the pacemaker under 1 cm bolus. A standard head-and-neck VMAT plan was generated in Eclipse and a setup CBCT was acquired prior to plan delivery. MOSFETs were localized on CBCT, and readings were compared to their corresponding treatment planning system point dose.
Results
Across all measurements, MOSFET readings were within ±5.4% of ion-chamber reference. The most significant differences occurred with high-SSD electron setups and beam energy variations (15-20%). These correspond to geometries where the MOSFET and ion-chamber sample different effective depths within the steep-gradient build up region, highlighting the need to account for detector depth and MOSFET placement when interpreting results. No significant trends were identified with dose rate or FF versus FFF delivery. For end-to-end measurements, the MOSFET and treatment planning system agreed within 7%, with MOSFETs visible on CBCT despite high-density artifacts from the pacemaker.
Conclusion
End-to-end validation demonstrates that MOSFETs provide suitable dosimetric accuracy, negligible dose-rate dependence, and sufficient visibility on CBCT imaging, making them suitable for in-vivo dosimetry for CIEDs. However, placement and geometry must be properly assessed when comparing dosimetric results across varying energies.