TH-CD-BRA-07: Range Verification System Using Scintillator and CCD Camera for the Scanning Irradiation System

Abstract

Purpose: To compress the quality assurance time for the scanned carbon-ion beam system, we have been developed the novel range verification system using scintillator and CCD (charge-coupled device) camera. Methods: A cylindrical plastic scintillator block and a CCD camera were installed on the black box. The range was determined by image processing. Reference range for each energy beam was determined the 80 percent of distal dose of the depth dose distribution that were measured by a large parallel-plate ionization chamber. Carbon beams ranging from 151.9 to 430 MeV/n were tested and compared with reference range. The common reference point of range is distal 80% of the dose distribution. In order to select the best reference point on a light distribution, the authors compared two range detection. Methods: threshold method (TH); the threshold positions set by the range from 10 to 90% of maximum value on the projected line are identified and difference of Gaussian (DOG) method. Using DOG method, range position is determined by zero-crossing position in the difference between small-Gaussian smoothed data and large-Gaussian smoothed data. Results: The 1 mm range difference was clearly detected. Standard deviation of discrepancy from the range measured by the ionization chamber was less than 0.1 mm. A 1 mm setup error in the any direction was less than 0.2 mm range error. Conclusion: We have shown that the range of carbon beam can be determined with sub-millimeter accuracy using scintillator and CCD camera. The 80 percent of maximum value is minimized discrepancies between expected and measured ranges for carbon beam. It was supposed to be a Result of the change of shape due to quenching effect. Since the system determine the range with short time and sufficient accuracy, it seems be that the system has potential to play the daily range check system.