Experience of using MOSFET detectors for dose verification measurements in an end-to-end 192Ir brachytherapy quality assurance system

Abstract

PurposeEstablishment of an end-to-end system for the brachytherapy (BT) dosimetric chain could be valuable in clinical quality assurance. Here, the development of such a system using MOSFET (metal oxide semiconductor field effect transistor) detectors and experience gained during 2 years of use are reported with focus on the performance of the MOSFET detectors. Methods and MaterialsA bolus phantom was constructed with two implants, mimicking prostate and head & neck treatments, using steel needles and plastic catheters to guide the 192Ir source and house the MOSFET detectors. The phantom was taken through the BT treatment chain from image acquisition to dose evaluation. During the 2-year evaluation-period, delivered doses were verified a total of 56 times using MOSFET detectors which had been calibrated in an external 60Co beam. An initial experimental investigation on beam quality differences between 192Ir and 60Co is reported. ResultsThe standard deviation in repeated MOSFET measurements was below 3% in the six measurement points with dose levels above 2 Gy. MOSFET measurements overestimated treatment planning system doses by 2–7%. Distance-dependent experimental beam quality correction factors derived in a phantom of similar size as that used for end-to-end tests applied on a time-resolved measurement improved the agreement. ConclusionsMOSFET detectors provide values stable over time and function well for use as detectors for end-to-end quality assurance purposes in 192Ir BT. Beam quality correction factors should address not only distance from source but also phantom dimensions.