Synthetic diamond devices for radiotherapy applications: Passive and active Dosimetry

For all its remarkable properties, diamond is well known as an interesting material for radiation detection and more particularly for medical uses. Natural diamond use for detection application is limited because of its high cost and the severe gem selection needed to fabricate reproducible and reliable devices. The recent progress of the chemical vapour deposition (CVD) technique offers new possibilities in the fabrication of ionisation chambers as well as thermoluminescent dosimeters for the particular field of radiotherapy. This paper presents the use of CVD diamond for both applications. For the use of diamond for TL applications, the purpose of this study was to control the trapping levels in the material with deliberate incorporation of impurities in CVD diamond film during the growth. For ionisation chamber fabrication, the aim was to purposely incorporate defects (with nitrogen incorporation) in the material in order to better understand the modification of the charge transport during irradiation. The first results obtained when the device is used to monitor the beam fluency of a medical accelerator facility are presented here. For both applications, several preliminary dosimetric parameters were probed and namely the reproducibility of the response, the linearity of the signal with the dose, and for TL dosimeters, both the optical and thermal fadings were carefully studied. Results are extremely encouraging and lead to interesting prospects for the use of diamond for dosimetry.