Monte Carlo study of the energy response and depth dose water equivalence of the MOSkin radiation dosimeter at clinical kilovoltage photon energies

Abstract

Skin dose is often the quantity of interest for radiological protection, as the skin is the organ that receives maximum dose during kilovoltage X-ray irradiations. The purpose of this study was to simulate the energy response and the depth dose water equivalence of the MOSkin radiation detector (Centre for Medical Radiation Physics (CMRP), University of Wollongong, Australia), a MOSFET-based radiation sensor with a novel packaging design, at clinical kilovoltage photon energies typically used for superficial/orthovoltage therapy and X-ray CT imaging. Monte Carlo simulations by means of the Geant4 toolkit were employed to investigate the energy response of the CMRP MOSkin dosimeter on the surface of the phantom, and at various depths ranging from 0 to 6 cm in a 30 × 30 × 20 cm water phantom. By varying the thickness of the tissue-equivalent packaging, and by adding thin metallic foils to the existing design, the dose enhancement effect of the MOSkin dosimeter at low photon energies was successfully quantified. For a 5 mm diameter photon source, it was found that the MOSkin was water equivalent to within 3% at shallow depths less than 15 mm. It is recommended that for depths larger than 15 mm, the appropriate depth dose water equivalent correction factors be applied to the MOSkin at the relevant depths if this detector is to be used for depth dose assessments. This study has shown that the Geant4 Monte Carlo toolkit is useful for characterising the surface energy response and depth dose behaviour of the MOSkin.

Characterization of a MOSkin detector for in vivo skin dose measurements during interventional radiology procedures

“…The percentage depth-dose response of the MOSkin detector was investigated previously, 41,45 which compared the MOSkin detector response with Markus chamber and Monte Carlo simulations in water. In their reports, the MOSkin detector showed an over-response compared with the Markus chamber measurements, 41 while Monte Carlo simulations showed MOSkin to have good agreement with simulated water response (±3%).…”

“…In their reports, the MOSkin detector showed an over-response compared with the Markus chamber measurements, 41 while Monte Carlo simulations showed MOSkin to have good agreement with simulated water response (±3%). 45 In this study, Fig. 6 shows the percentage depth-dose curves for the MOSkin and Markus ion chamber.…”

“…These data are in good agreement with the Monte Carlo simulations for the 100 kVp beam (effective photon energy of 48.6 keV). 45 The MOSkin detector for this study was calibrated and measured for the effective photon energy of 42.76 keV. Figure 7 shows the dose measured by the MOSkin and the Markus chamber corrected for inverse square law.…”

Measurement of multi-slice computed tomography dose profile with the Dose Magnifying Glass and the MOSkin radiation dosimeter

“…The MOSkin dosimeter, designed and developed at the Centre for Medical Radiation Physics (CMRP), University of Wollongong, Australia, has previously been investigated for applications in radiation therapy (Hardcastle et al, 2008;Kwan et al, 2009) and recently in CT (Lian et al, 2012). It was found to be tissue equivalent at depth in clinical kilovoltage beams (Lian et al, 2011) and was therefore selected as our gold standard absolute dosimeter in this work.…”

Organ point dose measurements in clinical multi slice computed tomography (MSCT) examinations with the MOSkin™ radiation dosimeter

“…The MOSkin TM dosimeter, designed at the Centre for Medical Radiation Physics (CMRP), University of Wollongong, Australia, is a radiolucent, easily implementable, real-time radiation dosimetry system built on MOSFET technology (Rozenfeld 2008 ). It was previously characterised in clinical kilovoltage x-ray photon beams (Lian et al 2011) and…”