Determination of absorbed dose to water from a miniature kilovoltage X-ray source using a parallel-plate ionization chamber.

This article presents a formalism for calculating and independently verifying the absorbed dose to water from a kV x-ray source (The INTRABEAM System) measured in a water phantom with an ionization chamber calibrated in terms of air-kerma. This formalism uses a Monte Carlo (MC) calculated chamber conversion factor, <i>C<sub>Q</sub></i>, to convert from air-kerma in a reference beam to absorbed dose to water in the measurement beam. In this work <i>C<sub>Q</sub></i> was determined for a PTW 34013 parallel-plate ionization chamber. Our results show that <i>C<sub>Q</sub></i> was sensitive to the chamber plate separation tolerance, with differences of up to 15 %. <i>C<sub>Q</sub></i> was also found to have a depth dependence which varied with chamber plate separation (0 to 10 % variation for the smallest and largest cavity height, over 3 to 30 mm depth). However for all chamber dimensions investigated, <i>C<sub>Q</sub></i> was found to be significantly larger than the manufacturer reported value, suggesting that the manufacturer recommended method of dose calculation could be underestimating the dose to water. PMID: 29059056 [PubMed - as supplied by publisher]
Source: Physics in Medicine and Biology - Category: Physics Authors: Tags: Phys Med Biol Source Type: research