Development and Verification of a Batch-Calibration Method for Plastic Scintillator In-Vivo Dosimetry
Abstract
Purpose
To develop a reliable batch‑calibration method and dose‑reading protocol for in-vivo scintillation imaging dosimetry during radiation therapy.
Methods
Plastic scintillators (DoseDots, 1.5 cm diameter; DoseOptics) were positioned at a series of known coordinates on an IC Profiler (Sun Nuclear Corporation). Placement accuracy was ensured with a laser‑cut acrylic template. The setup was irradiated at 100 cm source‑to‑surface distance (SSD) using a 6 MV, 30×30 cm² photon beam. Light emitted from each scintillator was recorded at 16 fps with a gated, intensified CMOS camera (DoseOptics LLC). Using the same beam parameters, dose measurements were performed in a water tank at depths 1 mm (water‑equivalent depth of the DoseDots) and 9 mm (effective measurement point of the profiler ion chambers). This allowed for the extrapolation of the profiler‑reported doses to the exact locations of the DoseDots. Raw images were background subtracted and flat‑field corrected. In each frame, the scintillation signal from each DoseDot was fitted to an ellipse, and peak amplitudes were summed across all frames to yield cumulative intensity per DoseDot. Calibration factors for various batches of DoseDots were expressed in counts/cGy. Additionally, dose‑linearity (40-800cGy), dose‑rate dependence (100-600 MU/min), and energy dependence (6-18 MV) were evaluated.
Results
The derived calibration factors demonstrated high intra-batch consistency with a coefficient of variation (CV) of 1.0%. Each DoseDot exhibited a linear dose response (R²=0.99) over the tested range. Dose-rate dependence and energy dependence tests yielded CVs of 2.6% and 1.6%, respectively.
Conclusion
The proposed workflow yields highly reproducible calibration factors, minimal dose-rate and energy dependence, as well as robust linearity, all of which are key for reliable, batch-calibration of plastic scintillators for in-vivo patient dosimetry.