Scintillator–CCD camera system light output response to dosimetry parameters for proton beam range measurement

Abstract

The purpose of this study is to investigate the luminescence light output response in a plastic scintillator irradiated by a 67.5MeV proton beam using various dosimetry parameters. The relationship of the visible scintillator light with the beam current or dose rate, aperture size and the thickness of water in the water-column was studied. The images captured on a CCD camera system were used to determine optimal dosimetry parameters for measuring the range of a clinical proton beam. The method was developed as a simple quality assurance tool to measure the range of the proton beam and compare it to (a) measurements using two segmented ionization chambers and water column between them, and (b) with an ionization chamber (IC-18) measurements in water.We used a block of plastic scintillator that measured 5×5×5cm3 to record visible light generated by a 67.5MeV proton beam. A high-definition digital video camera Moticam 2300 connected to a PC via USB 2.0 communication channel was used to record images of scintillation luminescence. The brightness of the visible light was measured while changing beam current and aperture size. The results were analyzed to obtain the range and were compared with the Bragg peak measurements with an ionization chamber. The luminescence light from the scintillator increased linearly with the increase of proton beam current. The light output also increased linearly with aperture size. The relationship between the proton range in the scintillator and the thickness of the water column showed good linearity with a precision of 0.33mm (SD) in proton range measurement. For the 67.5MeV proton beam utilized, the optimal parameters for scintillator light output response were found to be 15nA (16Gy/min) and an aperture size of 15mm with image integration time of 100ms. The Bragg peak depth brightness distribution was compared with the depth dose distribution from ionization chamber measurements and good agreement was observed. The peak/plateau ratio observed for the scintillator was found to be 2.21 as compared to the ionization chamber measurements of 3.01. The response of a scintillator block–CCD camera in 67.5MeV proton beam was investigated. A linear response was seen between light output and beam current as well as aperture size. The relation between the thickness of water in the water column and the measured range also showed linearity. The results from the scintillator response was used to develop a simple approach to measuring the range and the Bragg peak of a proton beam by recording the visible light from a scintillator block with an accuracy of less than 0.33mm. Optimal dosimetry parameters for our proton beam were evaluated. It is observed that this method can be used to confirm the range of a proton beam during daily treatment and will be useful as daily QA measurement for proton beam therapy.