Performance of a fluorescent screen and CCD camera as a two-dimensional dosimetry system for dynamic treatment techniques

A two-dimensionally position sensitive dosimetry system has been tested for different dosimetric applications in a radiation therapy facility with a s canning proton beam. The system consists of a scintillating (fluorescent) s creen, mounted at the beam-exit side of a phantom and it is observed by a c harge coupled device (CCD) camera. The observed light distribution at the s creen is equivalent to the two-dimensional (2D)-dose distribution at the sc reen position. It has been found that the dosimetric properties of the syst em, measured in a scanning proton beam, are equal to those measured in a pr oton beam broadened by a scattering system. Measurements of the transversal dose distribution of a single pencil beam are consistent with dose measure ments as well as with dose calculations in clinically relevant fields made with multiple pencil beams. Measurements of inhomogeneous dose distribution s have shown to be of sufficient accuracy to be suitable for the verificati on of dose calculation algorithms. The good sensitivity and sub-mm spatial resolution of the system allows for the detection of deviations of a few pe rcent in dose from the expected (intended or calculated) dose distribution. Its dosimetric properties and the immediate availability of the data make this device a useful tool in the quality control of scanning proton beams. (C) 2000 American Association of Physicists in Medicine. [S0094-2405(00)019 09-X].