title: Small field measurements with a novel silicon position sensitive diode array.
abstract: DOSI, a novel dosimeter based on position sensitive detectors for particle physics experiments, was used for relative clinical dosimetry measurements in small radiotherapy fields. The device is capable of dynamic measurements in real time and provides sub-millimetre spatial resolution. The basic beam data for a stereotactic radiotherapy collimator system (BrainLAB) using 6 MV photons were measured and compared with the corresponding data acquired with a small diamond detector and a PinPoint ionization chamber. All measurements showed an excellent agreement between DOSI and the diamond detector. There was an increasing discrepancy between the relative output factors (ROF) measured with DOSI and those measured with the ionization chamber with decreasing field size, specifically for collimators with a diameter smaller than 15 mm. The percentage depth doses (PDD) were in agreement to better than 1% for all depths. The agreement on off-axis ratios (OAR) was better than 3% for all collimators, whereas the agreement on relative output factors (ROF) was at the 1% level. DOSI's fast read-out electronics made it possible for all measurements to be recorded within 45 min including time to change collimators. This should reduce the overall time for commissioning and QA measurements, an important factor especially for busy radiotherapy departments.
authors.affiliation: Rutherford Appleton Laboratory, Science and Technology Facilities Council, Chilton OX110QX, UK.
authors.forename: S
authors.initials: S
authors.lastname: Manolopoulos
authors.forename: C
authors.initials: C
authors.lastname: Wojnecki
authors.forename: R
authors.initials: R
authors.lastname: Hugtenburg
authors.forename: M A
authors.initials: MA
authors.lastname: Jaafar Sidek
authors.forename: G
authors.initials: G
authors.lastname: Chalmers
authors.forename: G
authors.initials: G
authors.lastname: Heyes
authors.forename: S
authors.initials: S
authors.lastname: Green
mesh_terms: D017076:Computer-Aided Design; D004581:Electronics / Q000295:instrumentation*; D004867:Equipment Design; D019544:Equipment Failure Analysis; D011829:Radiation Dosage; D011874:Radiometry / Q000295:instrumentation* / Q000379:methods; D015203:Reproducibility of Results; D012666:Semiconductors; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted / Q000295:instrumentation*; D012825:Silicon / Q000528:radiation effects*
chemical_list: D012825:Silicon