A Multi-Channel Plastic Scintillator for Real-Time VMAT TBI Dosimetry
Abstract
Purpose
We evaluate the performance of a 4-channel plastic scintillator for real-time dose monitoring during VMAT total body irradiations (TBI).
Methods
The HYPERSCINT RP-200 (Medscint Inc., Quebec, QC., Canada) plastic scintillator dosimeter was used to measure VMAT TBI fields delivered by a TrueBeam Linac on both solid water and custom Rando phantoms. For solid water measurements, twenty-five VMAT fields and eighteen static-dynamic TBI fields were delivered to a single scintillator channel positioned at the field center beneath a 1.5×3.0×3.0cm3 bolus. The scintillator/bolus assembly was placed on a 30×30×30cm3 solid water phantom at 85cm SSD (gantry 0) using a 6MV photon beam. To evaluate dosimetry at TBI field junctions, an additional ten VMAT and six static-dynamic TBI fields were delivered to a Rando phantom (includes custom fiberboard legs). Four scintillator/bolus pairs were positioned with surface guidance to sample dose from overlapping fields at four junction locations. The scintillator was calibrated for absorbed dose (cGy) under known reference conditions and verified with measurement. AAA v15.6 in the Eclipse treatment planning system (TPS) with bolus/phantom modeled was used for the expected predicted dose. Uncertainty related dose variation with scintillator placement was also quantified.
Results
Across solid water measurements, mean percentage dose difference between scintillator and TPS was 1.6%, with a maximum difference of 3.3%. A 1cm deviation in scintillator position produced up to a 10% change in measured dose. For junction measurements on the custom Rando phantom, mean and maximum percentage dose differences were 2.9% and 8.7%, respectively, when surface guidance was used to verify bolus/scintillator placement. A 1cm mispositioning at junction locations produced dose deviations of up to 15%.
Conclusion
A multi‑channel plastic scintillator provided reliable real‑time dose monitoring of VMAT TBI dose deliveries. This will enable real-time VMAT TBI treatment verification, especially in high uncertainty regions such as field junctions.