2D photon dosimetry with a scintillation fibre optic dosimeter
As part of clinical safety for radiation therapy, quality assurance is vital to ensure that the delivered dose matches the prescribed dose for any targeted volumes and surrounding healthy tissue. A challenge when measuring the beam quality, especially for smaller sized beams, is having a water equivalent dosimeter with a high spatial resolution and the ability to perform accurate 2D mapping. In this work we use a plastic scintillator fibre optic dosimeter to measure a 2D beam profile of a 6 MV CLINAC photon beam with field sizes 30 x 30 mm2 and 10 x 10 mm2. The results supplement commissioning dosimetry data measured with three commercial dosimeters - two ionisation chambers (Scanditronix/Wellhofer CC13 and CC01) and a diode detector (IBA PFD-3G diode). We find that the 2D scanning system can cover the entire larger field in 27 min using 2 mm steps, providing a quick and thorough mapping of the beam for quality assurance. This system allows the step size to be varied as desired, something arrayed detectors cannot do. We measure an average uncertainty of 1% inside the field and 5% outside the field, demonstrating this system as a viable method for thorough mapping of 2D fields and as a tool for complimenting ionisation chamber measurements in thorough clinical quality assurance.