SU‐E‐T‐198: Evaluation of Dosimetric Characteristics of MOSFET Dosimeter for the Quality Assurance of Photon and Electron Beams

Abstract

Purpose: To study the basic dosimetric characteristics of MOSFET dosimeter for its suitability on constructing the quality assurance phantom. Methods: For all the measurements, the high sensitivity MOSFET with standard bias settings (3mV/cGy) was used. Solid water phantoms were used for both photon and electron beams. Tests were performed for 60Co beams, 6 and 15MV photon beams and 9MeV electrons. The dose‐linearity of MOSFET was studied up to 500 cGy with small increment at lowerdoses. Results were compared with the farmer chamber for photons and PP chamber for electrons. Reproducibility of the MOSFET was studied for the absorbed dose of 100cGy. Beam symmetry was measured at 5‐cm off‐axis position for 15×15cm2 field and comparisons were made with the farmer chamber and EDR‐2 film for photons and PP chamber and Kodak Xomat‐V for electrons. Also, the beam quality index was derived by measuring the dose at 10 and 20cm depth for photon beams. Measurements were done for five different days and compared with ion chamber measurements. Results: The correlation co‐efficient (R2) for MOSFET and ion chamber linearity curve is 0.9999, 0.9999, 0.9998 and 0.9999 for 6MV, 15MV and 60Co beams and 9MeV electrons. High sensitivity MOSFET showed good linearity at lower doses even with standard bias settings. Reproducibility of the MOSFET is 1.680%, 1.815%, 1.7194% and 1.754% for 6MV, 15MV and 60Co beams and 9MeV electrons. Beam Symmetry measured with MOSFET showed maximum variation up to 4.2% where as ion chamber and EDR‐2 was within 2.7% and 3.1%. MOSFET over‐responded consistently at the off‐axis position. Quality index measured with MOSFET was within 0.701% and 1.355% for 6 and 15MV photons, whereas the ion chamber was within 0.450%. Conclusions: The high sensitivity MOSFET may be used as a dosimeter with proper cross‐calibration for the quality assurance phantom, which is under construction.