Room: Stars at Night Ballroom 1
Purpose: The aim of this study was to develop a delivery quality assurance system to verify three-dimensional (3D) dose distribution and multi-leaf collimator (MLC) movement simultaneously in helical tomotherapy.
Methods: We made the prototype detector for simultaneous verification using a cylindrical plastic scintillator (20 cm diameter and 15 cm thickness). When the plastic scintillator was irradiated, the scintillation light was emitted according to absorbed dose distribution, and collected by a cooled charge-coupled device (CCD) camera with a resolution of 16 bits. In this study, the characteristics of the developed system according to the amount of emitted light was evaluated, and then compared with 3D dose distribution calculated by the radiotherapy treatment planning system. A point spread function (PSF) defined by double gaussian was used to correct the scatter of the scintillation light in the plastic scintillator. After the determination of PSF, the MLC movements were examined from the scintillation light recorded in each frame.
Results: The relationship between the leaf opening time and the amount of light was linear, and the dose distribution and leaf opening time per projection could be obtained using the amount of light. Both of light distribution and dose distribution of the same IMRT plan showed similar shape. Average dose difference and the pass rate of gamma evaluation with 2%/2 mm were âˆ’0.9%Â±0.5% and 99%, respectively. As a result of examination of MLC movement, the sensitivity and specificity of reconstructed sinogram showed more than 97%, and average leaf opening error was approximately 2%.
Conclusion: By measuring the scintillation light from the plastic scintillator with a CCD camera, the developed system enabled verification of both dose distribution and MLC movements in helical tomotherapy.
Funding Support, Disclosures, and Conflict of Interest: The present study was supported by JSPS KAKENHI Grant Number 18K15561.