Scintillating fiber dosimeter for radiation therapy accelerator

Radiotherapy accelerator requires high accuracy on dose deposition and their output has to be monitored on a frequent and regular basis. Ionization chambers are the main tool for this control, but their size and fragility make them unusable when performing a patient treatment. In collaboration with one of the French center for cancer treatment in Caen, we present the developments and tests of a low cost radiotherapy dosimeter (SDM) based on scintillating fiber and a signal processing for Cerenkov cancellation. The use of photodiodes for light collection insures a very low cost compared with system using PMTS. However we have also develop a high sensitivity version with PMTS for very "low dose deposition" for curietherapy or radiological exams. Comparison with standard ionization chamber has been performed showing about one percent difference from 6 to 25 MV photons. This dosimeter is 1 mm in diameter and can be located where ever is necessary even inside the body. Its small size and flexibility make it useful for delimiting critical area, where organs cannot be over-irradiated.