Novel Three-Dimensional Dose Distribution Measurement System for Volumetric Modulated Arc Therapy
Abstract
Purpose
This study aimed to develop a three-dimensional dose distribution measurement system using a plastic scintillator (PS), cooled charge-coupled device (CCD) camera, and electronic portal imaging device (EPID).
Methods
A prototype detector consisting of a cylindrical PS (20 cm in diameter and 15 cm in thickness), cooled CCD camera, and EPID was developed. When the PS was irradiated, scintillation light was emitted in proportion to the absorbed dose. The scintillation light was recorded using a cooled CCD camera set to 512 × 680 pixels, 16-bit grayscale, and 8.1 frames per second. This study evaluated the relationship between scintillation light intensity and absorbed dose, as well as the dependence on dose rate. Subsequently, static field and VMAT irradiations were performed using a 10 MV X-ray beam generated by TrueBeam. The three-dimensional light distribution was reconstructed by utilizing the scintillation light captured during irradiation, along with the fluence distribution obtained from the EPID. This reconstructed light distribution was then compared to the dose distribution calculated using a radiation treatment planning system.
Results
The relationship between scintillation light intensity and absorbed dose was linear. The variation in the scintillation light intensity was limited to 0.03% within the dose-rate range of 100-600 MU/min. The reconstructed light distribution closely resembled the calculated dose distribution. At the center of the static field irradiation, the mean dose difference and the gamma analysis pass rate, using the criteria of 3%/2 mm, were 0.40 ± 0.18% and 100%, respectively. For the VMAT irradiation, these values were 0.50 ± 0.26% and 97.5%, respectively.
Conclusion
The developed system facilitated precise measurement of three-dimensional dose distributions by capturing the scintillation light from the PS and the fluence distribution from the EPID.