Development of a Four-Dimensional Dose Distribution Verification System Using a Plastic Scintillator and Semiconductor Detector Array: Evaluation of Agreement between Measured Light Distribution and Planned Dose Distribution
Abstract
Purpose
Our research group developed a four-dimensional (4D) dose distribution verification system consisting of a cylindrical plastic scintillator (PS) and multiple semiconductor detector array. In this study, agreement between measured light distribution and planned dose distribution was evaluated.
Methods
The developed system consisted of the PS (15 cm diameter and 29 cm height) and multiple semiconductor detector array (ArcCHECK, SunNuclear Corp., FL, USA). A 16-bit cooled Charge-Coupled Device (CCD) camera was used to record dynamic images of the three-dimensional scintillation light distribution integrated along the longitudinal axis. In this study, dose and dose-rate dependency of the amount of light recorded by the CCD camera, and agreement between recorded light distribution and dose distribution of intensity-modulated radiotherapy (IMRT) plan calculated by RayStation version 14.0 (RaySearch Laboratories AB, Sweden) were investigated. 6 MV and 10 MV photon beams of TrueBeam linac (Varian Medical Systems, Palo Alto, CA, USA) were used. Dose difference and pass rate of gamma-analysis (3%/2 mm) were calculated for the area above the 10% isodose curve. The scintillation light diffusion in the PS was corrected by a point spread function defined by a double Gaussian.
Results
Dose dependency was linear for absorbed dose ranging from 0.7 to 9.1 Gy at the center of the PS. Dose-rate dependency was within ±1% for absorbed dose-rate ranging from 0.7 to 4.6 Gy/min at the center of the PS. Light distribution and dose distribution of IMRT plan showed good agreement, with the mean dose difference of 0.26 ± 0.73% and the gamma-analysis pass rate of 99%.
Conclusion
These results indicate that absorbed dose can be obtained from light distribution. The developed 4D dose distribution verification system successfully obtained light distribution corresponding to absorbed dose distribution by recording scintillation light from the PS using the CCD camera.