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.

A Novel Device for Intravaginal Electronic Brachytherapy

“…That is, whereas the system's depth dose data were based on measurements done in water, our measurements were done in solid water. This is further supported by the findings of Meigooni et al (17) and Healy et al (18), who evaluated the difference between these two materials for kilovolt irradiation and found a difference of as much as 2.3%. In addition, the soft X-ray ionization chamber has Fig.…”

The Bland–Altman analysis: Does it have a role in assessing radiation dosimeter performance relative to an established standard?

“…For the dosimetry of low energy therapeutic x-ray beams, the accepted 'gold standard' is the Farmer type cylindrical ionisation chamber (Evans et al, 2001;Healy et al, 2005;Hill et al, 2007Hill et al, , 2005Hill et al, , 2009Jurado et al, 2005;Li et al, 1997;Ma et al, 1998). This is consistent with the recommendations listed in the reference dosimetry protocols for kilovoltage x-ray beams (Aukett et al, 2005Ma et al, 2001).…”

“…A number of studies have evaluated different detector types for the dosimetry of low energy photon beams (Fletcher and Mills, 2008;Guillerminet et al, 2005;Healy et al, 2005;Hill et al, 2008;Hugtenburg et al, 2001;Jurado et al, 2005;Li et al, 1997;Ma et al, 1998;Nelson et al, 2008;Prestwich and Murphy, 2000;Rink et al, 2007;Sellakumar et al, 2009). There are limited recommendations by which a new detector should be tested in order that it can replace a gold standard detector.…”

The measurement of backscatter factors of kilovoltage X-ray beams using Gafchromic™ EBT2 film

“…The RMI-457 Solid Water phantom has been found to be radiologically water equivalent for low energy X-ray beams [38][39][40][41]. For the in-air measurements, no scattering material was present within at least 1 m from the cone to prevent unwanted scattered radiation interacting with the film.…”