Applications in radiation therapy of a scintillating screen viewed by a CCD camera

A two-dimensional (2D) dosimetry system has been designed for position-sensitive dose-measurement applications in modern radiation therapy. The system consists of a scintillating screen (Gd2O2S : Tb), observed by a low-noise CCD camera with a long integration time. The system allows reliable and accurate simultaneous 2D imaging of therapeutic dose distributions in the scintillator with sub millimeter spatial resolution. This system has been applied successfully at different applications in radiation therapy. Results of dose measurements in a treatment modality using a scanning proton beam are reported. It is shown that a quick and reliable measurement can be done. The screen+CCD system has proven to perform accurate dosimetry in applications where beams with a small (1–5 mm) diameter are used and where absolute dosimetry by means of standard ionization chambers is not possible due to their relatively large size. For the routine measurements of the alignment of therapeutic beams with respect to the tumor position, the system detects beam misalignments with an accuracy of 0.05 mm, which is more than sufficient to detect the maximum allowed misalignments in radiation therapy.