title: Measurements in radiotherapy beams using on-line MOSFET detectors.
abstract: When acquiring data to characterise radiation beams for radiotherapy treatment planning measurements in steep dose gradients such as beam penumbra or dose build-up are often required. A metal oxide semiconductor field effect transistor (MOSFET) with its inherent high spatial resolution was used for penumbra measurements in a 120 kVp X ray beam. The customised MOSFET system features a pulsed readout that allows the acquisition of data points in user defined time intervals of less than 1 s. Using a modified scanning beam data acquisition system the penumbra was acquired on-line in 0.1 mm steps. Measurements were made at different distances behind the beam collimator. From the extrapolation of the penumbra width to a location directly under the block the spatial resolution of the MOSFET system can be estimated to be better than 0.1 mm. This excellent spatial resolution has many potential applications in radiotherapy dosimetry, including the characterisation of multileaf collimator systems.
authors.affiliation: Newcastle Mater Misericordiae Hospital, Waratah, NSW, Australia. tomas.kron@ircc.on.ca
authors.forename: T
authors.initials: T
authors.lastname: Kron
authors.forename: A
authors.initials: A
authors.lastname: Rosenfeld
authors.forename: M
authors.initials: M
authors.lastname: Lerch
authors.forename: S
authors.initials: S
authors.lastname: Bazley
mesh_terms: D004867:Equipment Design; D005373:Film Dosimetry / Q000379:methods; D006801:Humans; D009862:Online Systems; D011874:Radiometry / Q000295:instrumentation / Q000379:methods*; D011878:Radiotherapy / Q000379:methods*; D015203:Reproducibility of Results; D012666:Semiconductors