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

• Published in: Physics in medicine & biology Vol. 63; no. 1; p. 015016
• Main Authors: Watson, Peter G F, Popovic, Marija, Seuntjens, Jan
• Format: Journal Article
• Language: English
• Published: England 19-12-2017
• Subjects: Brachytherapy - instrumentation; Brachytherapy - methods; Calibration; Humans; Monte Carlo Method; Phantoms, Imaging; Radiography - instrumentation; Radiography - methods; Water - chemistry; X-Rays
• ISSN: 1361-6560
• DOI: 10.1088/1361-6560/aa9560

Electronic brachytherapy sources are widely accepted as alternatives to radionuclide-based systems. Yet, formal dosimetry standards for these devices to independently complement the dose protocol provided by the manufacturer are lacking. 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, [Formula: see text], to convert air-kerma in a reference beam to absorbed dose to water in the measurement beam. In this work [Formula: see text] was determined for a PTW 34013 parallel-plate ionization chamber. Our results show that [Formula: see text] was sensitive to the chamber plate separation tolerance, with differences of up to 15%. [Formula: see text] 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, [Formula: see text] 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.