Grant: Travel Awards - Institute Community Support

Brachytherapy is the treatment of cancer using radiation sources placed as close as possible to tumour tissue. These sources have traditionally been radioactive seeds, however, a new class of electronic miniature X-ray sources have been recently introduced which offer a number of advantages over radioactive sources, such as reduced regulatory and shielding requirements. One drawback to these electronic sources is the difficulty in accurately measuring the amount of radiation emitted by these devices (a quantity known as 'dose'). By better understanding the uncertainties in this measurement, we can work towards reducing them. In this work, we evaluate the uncertainties in the measurement of dose from a commercially available miniature X-ray system (INTRABEAM). Dose measurements were performed in a water tank using a radiation detector (ionization chamber). The dose was calculated from the ionization chamber signal by two methods: 1) the formula recommended by the manufacturer, and 2) our own formula, which involves a pre-calculated conversion factor. This conversion factor was determined using a Monte Carlo particle transport simulation (EGSnrc). The sources of uncertainty investigated were: A) source positioning accuracy, B) ionization chamber dimension uncertainty, and C) statistical uncertainty. It was found that the measurement uncertainty can be as large as 8.9%, and decreases as a function of distance away from the INTRABEAM source. The dominant source of uncertainty was the positioning error, followed by the ionization chamber dimension uncertainty. To further reduce this uncertainty, it is recommended that a different ionization chamber with more precise knowledge of dimensions be investigated. While this measurement uncertainty is significant, the dose as calculated using the recommended formula was shown to disagree with the results from our method by up to 14.8 %, well beyond the measurement uncertainties investigated in this work.