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. 2012 Mar 8;13(2):3699.
doi: 10.1120/jacmp.v13i2.3699.

In vivo proton dosimetry using a MOSFET detector in an anthropomorphic phantom with tissue inhomogeneity

Ryosuke Kohno  1 , Kenji Hotta, Kana Matsubara, Shie Nishioka, Taeko Matsuura, Mitsuhiko Kawashima
Affiliations

In vivo proton dosimetry using a MOSFET detector in an anthropomorphic phantom with tissue inhomogeneity

Ryosuke Kohno et al. J Appl Clin Med Phys. .

Abstract

When in vivo proton dosimetry is performed with a metal-oxide semiconductor field-effect transistor (MOSFET) detector, the response of the detector depends strongly on the linear energy transfer. The present study reports a practical method to correct the MOSFET response for linear energy transfer dependence by using a simplified Monte Carlo dose calculation method (SMC). A depth-output curve for a mono-energetic proton beam in polyethylene was measured with the MOSFET detector. This curve was used to calculate MOSFET output distributions with the SMC (SMC(MOSFET)). The SMC(MOSFET) output value at an arbitrary point was compared with the value obtained by the conventional SMC(PPIC), which calculates proton dose distributions by using the depth-dose curve determined by a parallel-plate ionization chamber (PPIC). The ratio of the two values was used to calculate the correction factor of the MOSFET response at an arbitrary point. The dose obtained by the MOSFET detector was determined from the product of the correction factor and the MOSFET raw dose. When in vivo proton dosimetry was performed with the MOSFET detector in an anthropomorphic phantom, the corrected MOSFET doses agreed with the SMC(PPIC) results within the measurement error. To our knowledge, this is the first report of successful in vivo proton dosimetry with a MOSFET detector.

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Figures

Figure 1
Figure 1. Comparison of Bragg curves obtained by using a parallel‐plate ionization chamber (PPIC) and MOSFET detectors for a 190 MeV proton beam.
Figure 2
Figure 2. In vivo proton dosimetry using the MOSFET detector with an anthropomorphic phantom.
Figure 3
Figure 3. Axial images of the head and neck region in an anthropomorphic phantom, and isodose distributions calculated by the SMC. The Xs (black) represent the measurement points; the blue line is the target region.
Figure 4
Figure 4. Comparison of doses obtained by the uncorrected MOSFET detectors (MOSFET:raw), PBA, and SMC at measurement points A–G.
Figure 5
Figure 5. Comparison of doses obtained by the corrected MOSFET detectors with the PBA (MOSFET:PBA), the corrected MOSFET detectors with the SMC (MOSFET:SMC), and SMC at measurement points A–G.
See this image and copyright information in PMC

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