Charge Coupled Device Camera–Scintillator System for Two Dimensional Proton Dose Measurements

Abstract

A two-dimensional dosimeter composed of a charge coupled device (CCD) camera and a scintillating screen has been tested for measuring the dose distributions of therapeutic proton beams in situ. The dosimeter is the main component of the dosimetry system designed for the quality assurance of scanning beams in the course of patient treatments. A thin-wall parallel plate ionization chamber was built as part of the system to scale the beam currents, and a collimator and variable-thickness phantom being the other components. The system has been tested using a 40 MeV proton beam in a nontherapeutic beam line. The light output from the screen was linear within 0.1% at the typical dose rates of 1–2 Gy/min. The depth dose distributions were measured using the CCD camera system, and agreed well with the measurements by a calibrated ionization chamber. The CCD camera was also used to measure the beam intensity distributions produced with a Cu scatterer in the beam line. The comparison with the results of Monte Carlo simulations using MCNPX was useful for validating the code.