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Fade and Warm Up of MOSFET Dosimeters

D Plenkovich

D Plenkovich*, Memorial Hospital of Sweetwater County, Rock Springs, WY


PO-BPC-Exhibit Hall-19 (Saturday, March 5, 2016)  Room: Exhibit Hall

Purpose: It is generally believed that the MOSFET dosimeters have fade, or that their response changes with time. The fade component of the MOSFET dosimeter’s response is supposed to be <3%. In this presentation, it will be demonstrated that in the mobileMOSFET system (Best Medical Canada) fade can be almost completely eliminated with a proper warm up.

Methods: Five Standard Sensitivity, Single MOSFET dosimeters were used in this study. They were taped on the Calibration Jig, which was placed on 7 cm of Virtual Water slabs for backscatter. The MOSFET dosimeters were covered with 1.5 cm thick bolus. The SSD to surface of bolus was 100 cm, and the field size was 10 cm x 10 cm. The MOSFET dosimeters were irradiated with 100 MU and the 6 MV photon beam, the output of which has been calibrated and adjusted. The sequential reading feature in the mobileMOSFET software enables reading the dose data periodically or in predetermined intervals. The incremental dose to the MOSFET dosimeters was read in 60-second intervals.

Results: The fade component of the radiation dose was significant in the first three hours of measurement. Three and half hours after the irradiation of dosimeters, the measured dose leveled off very close to the expected value of 100 cGy. No fade effect could be seen.

Conclusion: The MOSFET dosimeters must be connected to the reader, which should have its power turned on. About three and half hours after the irradiation, the mobileMOSFET system reads the correct dose with almost no fade effect. This is the optimal time for calibration of the MOSFET dosimeters and for performing patient or beam output measurements.

Funding Support, Disclosures, and Conflict of Interest: Best Medical Canada has provided MOSFET dosimeters and build-up caps for this project.

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