The characteristics of diamond detector and its performance in small photon beams

Abstract

An ideal radiation detector for small photon beam should have the properties of high radiation sensitivity, high spatial resolution, constant response and soft tissue equivalent. The objectives of this study were to investigate the characteristics of PTW Riga diamond detector type 60003 and evaluate its performance in small fields of 6 MV photon beams. The characteristics of diamond detector were studied for polarization effect, repeatability, reproducibility and linearity of response, dependence on; dose-rate, beam energy, and direction. Performance of diamond detector was compared with those of Scanditronix Wellhofer p-type silicon diode and 0.13 cc ionization chamber (CC13) by measurements for field sizes of 1.5×1.5-10×10 cm2 which included output factors (OF), percentage depth doses (PDD), and beam profiles. Pre-irradiation dose of 5 Gy was required to solve the polarization effect and stabilize detector response. After pre-irradiation, the standard deviation was 0.16% in 10 repeated measurements and 0.4% for reproducibility in 1 month, 1 week apart. Diamond detector showed good linearity of response with the dose range studied of 1-400 cGy. The diamond to ion chamber response ratio were 1.008 to 0.995 for dose-rate varied from 1.58 to 4.69 Gy/min. Diamond detector showed no dependence on beam energy, slightly dependence on beam direction. Output factors measured by diamond detector were comparable with that measured by diode and CC13 for the field size greater than 2×2 cm2 and increasing to 2.3% for 1.5×1.5 cm2 with higher dose by diamond detector. For PDD measurements, the deviations between diamond-diode and diamond-CC13 were higher than 2% at the depth deeper than 15 cm. For beam profile measurement, radiological width (RW50) measured by diamond detector were comparable with those by diode and CC13 for 10×10 cm2 field size and larger than the others for small field size. Penumbra width (80-20%) measured by diamond detector was also larger than diode but smaller than CC13 for all field sizes study. For small field of photon beam, the diamond detector has suitable characteristics and performance for dosimetric applications. Due to its tissue equivalent property, the diamond detector is superior to the diode. However, the user should be attending to pre-irradiation process which relates to the stability of detector response.