CLINICAL DOSIMETRY USING MOSFETS

Purpose: The use of metal oxide-silicon field effect transistors (MOSF ETs) as clinical dosimeters is demonstrated for a number of patients w ith targets at different clinical sites. Methods and Materials: Commer cially available MOSFETs were characterized for energy response, angul ar dependency of response, and effect of accumulated dose on sensitivi ty and some inherent properties of MOSFETs. The doses determined both by thermoluminescence dosimetry (TLD) and MOSFETs in clinical situatio n were evaluated and compared to expected doses determined by calculat ion, Results: It was observed that a standard calibration of 0.01 Gy/m V gave MOSFET determined doses which agreed with expected doses to wit hin 5% at the 95% confidence limit for photon beams from 6 to 25 MV an d electron beams from 5 to 14 MeV. An energy-dependent variation in re sponse of up to 28% was observed between two orientations of a MOSFET, The MOSFET doses compared very well with the doses estimated by TLDs, and the patients tolerated MOSFETs very well, A standard deviation of 3.9% between expected dose and MOSFET determined dose was observed, w hile for TLDs the standard deviation was 5.1%. The advantages and disa dvantages of using MOSFETs for clinical dosimetry are discussed in det ail, Conclusion: It was concluded that MOSFETs can be used as clinical dosimeters and can be a good alternative to TLDs, However, they have limitations under certain clinical situations, (C) 1997 Elsevier Scien ce Inc.