title: Output factor measurements for a kilovoltage X-ray therapy unit.
abstract: Output factors at the surface for treatment cones and lead cut-outs have been measured for a Pantak Therapax SXT 150 superficial therapy unit with x-ray beam qualities from 1 to 13 mm A1 HVL. A variety of phantom materials and two ionisation chambers were tested for their suitability in output factor and percentage depth dose measurement. Solid water proved a useful water-equivalent phantom material with discrepancies between measurements in water and solid water less than 2.3% for percentage depth dose and less than 0.6% for output factors. Larger measurement discrepancies were found for Plastic Water and Perspex. A PTW Markus chamber was found to compare well with a NE 2532/3 low energy chamber in percentage depth dose measurement, but discrepancies arose between the chambers in output factor measurements, up to 5% for small field sizes. Measurements indicated that the Markus chamber had an energy dependent response in the kilovoltage range, which could account for the discrepancy in output factor measurement.
authors.affiliation: Southern Zone Radiation Oncology Service--Mater Centre, Princess Alexandra Hospital, Brisbane, Australia. brendan_j_healy@health.qld.gov.au
authors.forename: B J
authors.initials: BJ
authors.lastname: Healy
authors.forename: A
authors.initials: A
authors.lastname: Gibbs
authors.forename: R L
authors.initials: RL
authors.lastname: Murry
authors.forename: J E
authors.initials: JE
authors.lastname: Prunster
authors.forename: K N
authors.initials: KN
authors.lastname: Nitschke
mesh_terms: D001315:Australia; D019544:Equipment Failure Analysis / Q000379:methods* / Q000592:standards; D017408:Guidelines as Topic; D011785:Quality Assurance, Health Care / Q000379:methods*; D011829:Radiation Dosage; D011874:Radiometry / Q000379:methods* / Q000592:standards; D012015:Reference Standards; D014964:X-Ray Therapy / Q000295:instrumentation* / Q000379:methods