Author: Maria F. Chan, Indra J. Das, Xiuxiu He, Seng Boh Gary Lim, Jeonghoon Park, Yunjie Yang 👨🔬
Affiliation: Department of Medical Physics, Memorial Sloan Kettering Cancer Center, Northwestern Memorial Hospital, Northwestern University Feinberg School of Medicine, Memorial Sloan Kettering Cancer Center 🌍
Purpose: There is a need for accurate and flexible in-vivo dosimetry systems, particularly for special procedures. Effective dosimetry is crucial for dose verification and maintaining records. A new radiochromic film-based in-vivo dosimetry system is investigated, commissioned, and benchmarked for clinical use.
Methods: Each radiochromic film-based device is individually packed with a unique QR code. The calibration process involves an automated scanning process at user-specified time intervals, with auto-ROI detection and triple-channel calibration, to capture the time-resolved post-irradiation optical density growth. Two standard Epson scanner models (V600/13000XL) were used to cross-validate readouts. The dosimetric accuracy was evaluated for 15-400 cGy. Angular dependence was studied in 45° increments over 360° compared to the response at 0° at 250 cGy using a cylindrical phantom. Energy dependence was evaluated for four photon energies (6MV,6FFF,10FFF,15MV) and five electron energies (6-20 MeV) using 3 Linacs. Long-term reproducibility/stability were assessed with nine devices with seven different doses under identical conditions over one month.
Results: The system provides accurate dose measurements across high and low dose ranges. All readings were within specification: accuracy was <±5 cGy for doses ≤80 cGy doses, and <±5% for doses >80 cGy. Angular dependence showed a maximum variation of 2.6±0.3% when the beam passed through the posterior oblique side of the device. Daily QC/reproducibility tests confirmed system constancy. Energy dependence analysis revealed deviations of up to 4.3±0.5% for all photon and electron energies compared to 6MV photons, indicating the need for energy correction during commissioning. Both scanners provided comparable readouts within 1%. Based on these findings, the user guidelines were established to ensure optimal performance and accuracy.
Conclusion: The new film-based in-vivo dosimetry system provides a straightforward workflow that enables consistent, time-independent, and near real-time readout with a user-friendly design that simplifies handling and analysis, thereby streamlining in-vivo dosimetry measurements.