An EGS4 Monte Carlo examination of the response of a PTW-diamond radiation detector in megavoltage electron beams

The EGS4 Monte Carlo code has been used to investigate the response of a PTW/diamond detector irradiated in both clinical and monoenergetic megavoltage electron beams ranging in energy from 5 to 20 MeV. The sensitive volume of the PTW/diamond detector simulated has a thickness of 0.4 mm and a diameter of 4.4 mm. Irradiation was simulated at various depths in a water phantom. The results show that the PTW/diamond detector has a constant response (within 1.0%) in electron beams if irradiated at depths closed to d(max), and its response is almost independent of irradiation depth or incident electron energy (within 3%). A detailed examination of the average detector dose shows that the sensitive volume of the PTW/diamond detector acts as a Spencer-Attix cavity within 1%. The encapsulation of the bare diamond detector with low-Z epoxy and polystyrene wall material does not affect its response in electron beams. The difference in response between the unencapsulated (TLD) and the encapsulated form of the detector is less than 0.5% for all depths over electron energy range investigated. (C) 1999 American Association of Physicists in Medicine. [S0094-2405(99)00605-7].