3084 - Toward Clinical Deployment of Scintillator-Based In Vivo Dosimetry for Radiation Therapy: A Robust Batch Calibration Workflow
Presenter(s)
N. Mulenga1, J. E. Hallett2, M. Clark3, D. A. Alexander4, R. Vasyltsiv1, A. L. Matous4, L. A. Jarvis5, P. Bruza6, and D. J. Gladstone7; 1Dartmouth College, Hanover, NH, 2University of Wisconsin, Madison, WI, 3Stanford University, Stanford, CA, 4Dartmouth-Hitchcock Medical Center, Lebanon, NH, 5Dartmouth Health, Lebanon, NH, 6Thayer School of Engineering, Dartmouth College, Hanover, NH, 7Geisel School of Medicine at Dartmouth & Norris Cotton Cancer Center, Dartmouth Hitchcock Medical Center, Lebanon, NH
Purpose/Objective(s):
To develop a reliable batch-calibration method and dose-reading protocol for in-vivo scintillation imaging dosimetry during radiation therapy.Materials/Methods:
Plastic scintillators (1.5 cm diameter) were positioned at a series of known coordinates on an ion chamber (IC) Profiler. 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, 35×35 cm² photon beam. Light emitted from each scintillator was recorded at 16 fps with a gated, intensified CMOS camera. Using the same beam parameters, dose measurements were performed in a water tank at depths 1 mm (water-equivalent depth of the scintillators) 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 scintillators. Raw images were background subtracted and flat-field corrected. In each frame, the scintillation signal from each scintillator was fitted to an ellipse, and peak amplitudes were summed across all frames to yield cumulative intensity per scintillator. Calibration factors for scintillators 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 scintillator 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 across the clinically relevant dose range, key for reliable, batch-calibration of plastic scintillators for in-vivo patient dosimetry. Unlike conventional methods requiring individual, time-intensive calibration of each dosimeter, this protocol utilizes existing clinical QA equipment to efficiently establish reliable calibration factors for entire batches, addressing a critical barrier to clinical adoption. By enabling practical, traceable batch processing while maintaining rigorous dosimetric standards, this method facilitates the translation of plastic scintillator technology into routine clinical use for real-time in-vivo dosimetry during radiation therapy treatments.