Unlocking In-Vivo Dosimetry In HDR Brachytherapy with Plastic Scintillation Detectors through Experimentally Extracted and Validated Correction Factors
Abstract
Purpose
Experimentally extract and validate the correction factors, including ionization quenching, to be applied to dose rates measured with a Plastic Scintillation Detector (PSD) for In-Vivo Dosimetry (IVD) in High Dose Rate (HDR) brachytherapy.
Methods
A PRB-0080 PSD (1×3 mm3) in polystyrene was coupled to the Hyperscint RP-200 system (Medscint, QC, CA) to acquire dose rates at 1 and 10 Hz after calibration. Measurements used an Iridium-192 Flexisource (Elekta, The Netherlands) with SK=24512 and 29039 U. Correction factors for volume averaging (kvol), medium (pscint), and wall effects (pwall) were calculated using TOPAS Monte Carlo (MC) code v3.9 (Geant4-v10.7) and applied to the measurements. The PSD was positioned in an IBA Blue-Phantom2 water tank, whose dimension ensures full scatter conditions, and was automatically moved across the transverse plane (Θ=90°) in 0.3±0.032 cm step up to 19.3±0.083 cm from the source. First, the ionization quenching correction factor, kioq, was estimated from the residual relative difference (RD) between corrected dose rates, at 1 Hz, with other coefficients and MC calculated dose rates. For validation, dose rates were independently measured within the same setup, at 10 Hz, up to 15.2±0.083 cm. The kioq effectiveness was evaluated in terms of RDs compared to MC values.
Results
The correction factors kvol, pscint, and pwall ranged between [1.003-1.000], [1.034-1.067], and [1.002-1.012], respectively, over distances from 1 to 20 cm. The extracted kioq factors ranged from 1.018 to 1.77 over the same distances and followed a quadratic function. Validation measurements showed RDs of less than 5 % up to 15.2±0.083 cm from the source when all correction factors are applied.
Conclusion
This study extracted all the correction factors necessary for accurate PSD measurements under HDR brachytherapy energy range. Future work will investigate and evaluate the ionization quenching using a different plastic and an inorganic scintillator for molecular dependencies.