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

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

doi:10.1120/jacmp.v13i2.3699

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 (SMCMOSFET). The SMCMOSFET output value at an arbitrary point was compared with the value obtained by the conventional SMCPPIC, 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 SMCPPIC results within the measurement error. To our knowledge, this is the first report of successful in vivo proton dosimetry with a MOSFET detector.PACS number: 87.56.‐v

Highlights

Comprehensive dose verifications are essential before radiation therapy with proton beams can be applied clinically
160 Kohno et al.: In vivo proton dosimetry chamber,(7) presumably because the metal-oxide semiconductor field-effect transistor (MOSFET) detector strongly depends on the linear energy transfer (LET) of the proton beam
To measure the proton dose in tissue inhomogeneities with a MOSFET detector, we developed a highly precise method using the simplified Monte Carlo dose calculation method (SMC) to correct the MOSFET response to proton beams

Summary

Introduction

Comprehensive dose verifications are essential before radiation therapy with proton beams can be applied clinically. 160 Kohno et al.: In vivo proton dosimetry chamber,(7) presumably because the MOSFET detector strongly depends on the linear energy transfer (LET) of the proton beam. These findings suggest that it may be difficult to measure the proton dose with a MOSFET detector. A correction factor for the response of the MOSFET detector was calculated as a function of the proton penetration depth. Because the protons at any point may have a variety of energies due to multiple scattering effects, the correction factor at an arbitrary point can be calculated with the pencil beam dose calculation algorithm (PBA).(10-12)

Methods

Results

Conclusion