Evaluation of MOSFETs for entrance dose dosimetry for 6 and 10 MV photons with a custom made build up cap.
Commercially available MOSFETs, Thomson and Nielsen TN502-RD, were evaluated for suitability as an entrance dose in vivo dosimeter for 6MV and 10MV. Detector response was normally distributed around a mean (skewness = -0.01 +/- 0.24, kurtosis = -0.09 +/- 0.48) with a mean of 110.6 mV/Gy, with a standard deviation of 2.4% at 0.86 Gy. The standard deviation of readings increased with decreasing dose and increased at a rate greater than inverse square. The linearity coefficient was 0.9999. No significant dependence on angle, field size, dose rate, energy or time was observed. As such, they would be useful for entrance dose in vivo dosimetry. With a custom made build up cap corrections were required for field size, wedge, beam energy and tray factors, showing that build up cap design is an important consideration for entrance dose in vivo dosimetry using MOSFETs.
Department of Physics and Engineering. Adelaide Radiotherapy Centre, Adelaide, Australia. jmorton@adradcentre.com.au
J P
JP
Morton
M
M
Bhat
A
A
Kovendy
T
T
Williams
D017785:Photons; D011829:Radiation Dosage; D011874:Radiometry / Q000295:instrumentation*; D015203:Reproducibility of Results