Room: AAPM ePoster Library
Purpose: Verification of delivery is important in dynamic delivery such as volumetric modulated arc therapy and scanned particle therapy. We developed the scintillator imaging system to measure the 3D dose distribution with high-sampling rate and performed the 2D/3D gamma evaluation to the measured data.
Methods: Our system was composed of a column-shaped plastic scintillator covered by a Gd2O2S: Tb intensifier screen, a truncated cone-shaped mirror and a cooled CCD camera. The metal artifact produced by the intensifier screen was problem to calculate the dose by the RTPS. Monte Carlo simulation, therefore, was used to acquire the calculated dose distribution as the reference. The scintillator was irradiated with 6MV photon beams. Shape of the irradiated field was the square shape (16- and 20-mm) and the step shape. Our algorithm is following, 1) Deconvolution processing; 2) convert light intensity to dose; 3) reconstruction processing. Linear combination of a 2D Lorentzian function and a 2D Gaussian function was used and the parameter of this function was optimized by minimizing the cost function. Gamma evaluation with 3% and 2-mm criteria was performed to these dose volumes.
Results: Depth dose distribution by measurement was in good agreement with the calculation. Difference was within 2%, excluding the build-up region. All 2D gamma passing rate at the isocenter plane was over 95%. The results of 3D gamma evaluation for the 20-mm square field was 96.5%.
Conclusion: Scintillator imaging system could be measured the 3D dose distribution from each measured image. Measurement was analyzed by the 2D/3D gamma evaluation. Our system and algorithm lead to images in agreement with depth dose distribution and 3D dose distributions.
Funding Support, Disclosures, and Conflict of Interest: KAKEN: 18K15607