CVD Diamond X-ray Detectors for Radiotherapy Dosimetry S P Lansley †,* , G T Betzel, J Meyer Department of Physics & Astronomy University of Canterbury Christchurch, New Zealand † Also, MacDiarmid Institute for Advanced Materials & Nanotechnology, New Zealand * stuart.lansley@canterbury.ac.nz F Baluti Oncology Service Christchurch Hospital Christchurch, New Zealand L Reinisch Department of Physical & Earth Sciences Jacksonville State University Jacksonville, AL, USA Abstract— X-ray detectors were fabricated from a range of commercially-available synthetic diamond fabricated using chemical vapour deposition (CVD). As these detectors are intended as dosimeters for use in radiotherapy (beam calibration and profiling, in-situ dose measurements etc.), they were appropriately packaged and tested in a clinical environment, using clinical apparatus and following clinical procedures. The combination of linear dose-rate dependence of the photocurrent, negligible dark current levels (pA or less, compared to nA photocurrents), low priming doses (few Gy) and high specific sensitivities (of up to 460 nCGy -1 mm -3 , compared to reported values of 50–140 nCGy -1 mm -3 for a commercial natural diamond-based X-ray detector) demonstrates the potential of these devices as simple–to–use, small size, tissue-equivalent, sensitive X-ray dosimeters. I. INTRODUCTION Radiation detection and dosimetry play an important role in radiation environments such as hospital x-ray imaging and treatment facilities. Dosimetry is used during system calibration to assess beam characteristics for later use in treatment planning, but could also be used during patient exposure to confirm the exposure dose [1]. For radiotherapy, an ideal dosimeter has the following features: high accuracy – the ability to indicate physical dose correctly; high precision – the reproducibility of results under similar conditions; low detection limit – the lowest dose detectable; measurement range – it should be able to detect radiation over an appropriate dose range; linear dose response – readings should be linearly proportional to the given dose; dose-rate independence – readings should be independent of the dose- rate; energy independence – readings should be independent of the radiation energy; and high spatial resolution – it should allow the measurement of the dose in a very small volume [2]. Diamond has been proposed as a material for the construction of radiation detectors for many years, for reasons including its near-tissue equivalence – its atomic number (Z = 6) is close to that of tissue (Z ≈ 7.4) – and radiation hardness. Being a solid state material with high atomic density, it should be possible to realise small-volume detectors suitable for obtaining measurements with high spatial resolution. Also, it is expected that the response of detectors fabricated from diamond should be independent of the x-ray energy and dose rate. Early reports utilized carefully selected natural diamonds [3,4]. Natural diamond-based detectors for radiotherapy applications are commercially-available [5,6], but they are not widely used due to poor availability and high cost arising from the scarcity of suitable high-quality material. Recent developments in the synthesis of diamond have led to both chemical vapour deposition (CVD) [7-11] and high pressure high temperature (HPHT) [12-14] diamond being considered for radiotherapy dosimetry. The use of synthetic diamond should make possible the fabrication of cheaper diamond- based x-ray detectors with more reproducible characteristics, resulting from the possibility of controlling the quality of the diamond during synthesis. II. EXPERIMENTAL METHODS A. Material Commercially-available free-standing synthetic diamond films were purchased from three manufacturers; unless otherwise stated, the material was synthesised using chemical vapour deposition (CVD). Black, opaque polycrystalline films 5 × 5 mm 2 and 100, and 200 μm in thickness were obtained from Diamonex [15]. These films were ‘as grown’ with random crystallite S P Lansley is funded by the Foundation for Research, Science and Technology (FRST), New Zealand (through NZ Science and Technology Post-doctoral Fellowship UOCX0702) and the MacDiarmid Institute for Advanced Materials & Nanotechnology. G T Betzel is funded in part by Sigma Xi Grants-in-Aid of Research. 978-1-4244-5335-1/09/$26.00 ©2009 IEEE 1238 IEEE SENSORS 2009 Conference