Dosimetric characterisation of a polycrystalline diamond detector prototype in radiotherapy beams.

Polycrystalline diamond films were made and characterised in terms of structural parameters using Raman and Scanning Electron Microscopy techniques. A cvd diamond detector prototype was tested as on-line radiotherapy beam dosimeter biasing the detectorwith 100 V. The signal to noise ratio was 10 and a good linearity between the detector reading and the dose to water was achieved. The detector sensitivity was 30 nC gy-1 mm- 3 of detector sensitive volume. A power law with exponent equal to 0.92 was found to fit the detector average current as a function of the dose rate to water. The results show that a better detector current linearity with the dose rate can be achieved by supplying to the detector a bias voltage higher than 100V, on expense of the signal to noise ratio. However, when the dose rate dependence of the CVD detector signal was corrected, the percentage depth signal in a PMMA phantom along the x-ray beam central axis, and the relative output factor resulted in agreement with those obtained by a n ionisation chamber, confirming the water equivalence of the CVD detector.