Effect of MOSFET dosimeters' calibration method on calibration factors and radiation doses measured with the dosimeters in radiology.

MOSFET dosimeters have widely been used to measure radiation doses caused by x-rays. When using the MOSFET dosimeters, calibration factors (CFs) have a direct effect on reliability of dose measurements. The aim of this paper was to study the effect of various calibration methods on the CFs of the MOSFET dosimeters. The CFs were measured on clinical digital x-ray angiography (XA) and computed tomography (CT) devices using a calibrated CT ionization chamber and a standard polymethyl methacrylate (PMMA) phantom. The measurements were conducted by having the dosimeters (1) in air, (2) on the surface of the PMMA phantom and (3) inside the phantom. A statistically significant difference was seen between the CFs measured on the XA and CT devices. The CFs measured on the CT device were 20%-165% higher than those measured with the XA device (p < 0.001) in every calibration geometry. Furthermore, the calibration geometry had a notable effect on the CFs on CT. The CFs on the surface of the phantom were 18%-25% higher than in air (p < 0.05), and the CFs inside the phantom were 32%-39% smaller than in air (p < 0.05). These results suggest that the calibration of the MOSFET dosimeters should be conducted with the same device that is used in actual dose measurements. Also, the scattering conditions and the calibration geometry should be similar in the calibration and subsequent dose measurements.