To determine the source dwell positions of HDR brachytherapy using 2D 729 ion chamber array

The purpose of this study was to determine the dwell position of a high-dose- rate (HDR) brachytherapy Ir-192 source using a PTW Seven29 2D detector array. A Nucletron Microselectron HDR device and 2D array ionisation chamber, equipped with 729 ionisation chambers uniformly arranged in a 27 x 27 matrix with an active array area of 27 x 27 cm(2), were used for this study. Different dwell positions were assigned in the HDR machine. Rigid interstitial needles and a vaginal applicator were positioned on the 2D array, which was then exposed according to the programmed dwell positions. Subsequently, the positional accuracy of the source position was analysed. This process was repeated for different dwell positions. The results were analysed using an in-house- developed Excel programme. Different random dwell position checks as well as dwell position measurements were performed using a radiochromic film. The dwell positions measured by the 2D array were found to be in good agreement with those measured by the film. The standard deviations between the doses obtained from the different dwell positions were 0.191828, 0.329973, 0.370632 and 0.779939, whereas the corresponding standard deviations of the doses at the vaginal cylinder were 0.60303, 0.242808, 0.242808 and 0.065309. When the planned and measured dwell positions were plotted, a linear relationship was obtained.