Evaluation of a PTW diamond detector for electron beam measurements

Abstract

A PTW Riga diamond detector has been evaluated for use in electron beam dosimetry, by comparing results with those obtained using a diode (Scandihonix p s i ) and an ionization chamber (Scanditronix RK). The directional response of the diamond at 6 MeV and 15 MeV is more uniform than that of the dioide, but for both detecton there is a dip in response when the beam axis is perpendicular to the detector stem. Spatial resolution of the diode detector, measured beneath a 2 m m wide slit, is slightly better than that of the diamond detector with detector stems both parallel and perpendicular to the beam axis. Diamond and diode depthdose curves both agree well with corrected ionization chamber results at I5 MeV, while at 6 MeV the diamond is in better ageement. This indicates that the diode provides better spatial resolution than the diamond for measuring profiles, but the diamond is preferable for low-energy depth-iose measurements.

Characterization of a synthetic single crystal diamond Schottky diode for radiotherapy electron beam dosimetry

“…[2][3][4] In addition, spatial averaging effects due to the finite size of ionization chambers make them not suitable when high spatial resolution is required. 5 Although being not tissue-equivalent, silicon diodes (p-type) have been well established in clinical electron dosimetry due to their small sensitive volume, high sensitivity, and high spatial resolution. [6][7][8] The silicon to water stopping power ratio is fairly constant for electron energies between 5 and 25 MeV and, once calibrated against an ionization chamber, the diode response is assumed to represent the dose with no need of depth-dependent correction factors.…”

“…[11][12][13][14][15][16][17] Moreover, the carbon to water stopping power ratio stays nearly constant over an electron energy range 1-20 MeV; thus, allowing direct measurement of dose distributions in tissue equivalent medium. 1,5 Furthermore, unlike silicon diodes, the same diamond detector is expected to be suitable for both electron and photon dosimetry. 5 Most studies on diamond application for megavoltage electron and photon radiotherapy beam dosimetry have been performed using PTW natural diamond detectors and are reported as comparative investigations with respect to reference detectors, i.e., ionization chambers and silicon diodes.…”

Investigation of the suitability of commercially available CVD diamond for megavoltage X-ray dosimetry

“…Specific sensitivities values reported in the literature have been measured using a variety of x-ray (250 kV, and 6, 10, and 25 MV) and electron (4-25 MeV) energies from linear accelerators, as well as other radiation sources such as 60 Co and 90 Sr. For PTW natural diamond detectors the specific sensitivities lie in the range 50-140 nC·Gy -1 ·mm -3 [8,24,26,27,33]. A wide range of specific sensitivities have been reported for CVD diamond-based detectors, ranging from a few to over a thousand nC·Gy -1 ·mm -3 ; generally, the lower values (of up to ~100 nC·Gy -1 ·mm -3 ) appear to be reported for polycrystalline material grown in-house by the researchers [8,9,25,30,34], whereas the higher values were obtained using commercial CVD diamond, some of which was described as 'detector grade' [10,24,31,34,35].…”

The water‐equivalence of phantom materials beta particles

“…The central electrode of the pinpoint chamber is 1.6 mm from the outer surface and the position of the sensitive volume in the diamond detector is 1 mm from the surface. 8 Unlike the pinpoint chamber, the diamond detector does not require temperature and pressure corrections and has very little energy dependence. 8,9 Phantom materials This study investigated the properties of A150 plastic ͑Exradin, Lisle IL͒, Virtual Water™ ͑MED-CAL INC., WI͒ and polystyrene when used with beta particles.…”

“…8 Unlike the pinpoint chamber, the diamond detector does not require temperature and pressure corrections and has very little energy dependence. 8,9 Phantom materials This study investigated the properties of A150 plastic ͑Exradin, Lisle IL͒, Virtual Water™ ͑MED-CAL INC., WI͒ and polystyrene when used with beta particles. The Virtual Water is an epoxy-based water substitute equivalent to Solid Water™ ͑Gammex-RMI, Middleton WI͒.…”