The effect of rectal heterogeneity on wall dose in high dose rate brachytherapy

Abstract

When treating prostate cancer using high dose rate (HDR) brachytherapy, overdosing the rectal wall may lead to post-treatment rectal complications. An area of concern is related to how the rectal wall dose is calculated by treatment planning systems (TPSs). TPSs are used to calculate the dose delivered to the rectal wall, but they assume that the rectum is a water-equivalent homogeneous medium of infinite size and do not consider the effect that an air-filled "empty" rectal cavity would have on the dose absorbed along the rectal wall. The aim of this research is to quantify the effect that an air cavity has on the rectal wall dose, as its presence changes the backscatter conditions in the region. The MO Skin and RADFET dosimeters proved capable of measuring absolute dose with increasing distance from the HDR Ir-192 brachytherapy source. However, the anterior rectal wall doses measured by the MOSkin and RADFET in an empty rectal cavity were 14.7 +/- 0.2% and 13.7 +/- 0.6% lower than the dose measured in a homogeneous rectal phantom. Monte Carlo simulations corroborated the experimentally obtained results, reporting a -13.2 +/- 0.6% difference. The dose measured at the posterior wall of an empty rectal cavity was between 22% and 26% greater than the dose measured in a full rectal cavity. The heterogeneity of the rectal volume appears to have a significant effect on the rectal dose when compared to calculated rectal dose.

TRUS-probe integrated MOSkin detectors for rectal wall in vivo dosimetry in HDR brachytherapy: In phantom feasibility study

“…Some of these have already been used to perform in vivo prostate dosimetry by directly placing them in either a needle in the prostate, a catheter in the urethra or in the rectum (Seymour et al, 2011;Suchowerska et al, 2011 . More specific information about MOSkin dosimeters may be found elsewhere (Qi et al, 2007;Kwan et al, 2009). …”

Online in vivo dosimetry in high dose rate prostate brchytherapy with MOSkin detectors: In phantom feasibility study

“…In particular, great interest was dedicated to the application of MOSFETs to BT, because the typical large dose gradients achieved in BT necessitate a small detector with a reduced active volume for accurate dosimetry. In this work, a specific type of MOSFET dosimeter called "MOSkin" which has developed by the Centre for Medical Radiation Physics (CMRP) of the University of Wollongong (Australia) (Qi et al 2007, Kwan et al 2008, Kwan et al 2009 has been studied.…”

Measurement of multi-slice computed tomography dose profile with the Dose Magnifying Glass and the MOSkin radiation dosimeter

“…Table 1 shows the scan parameters used for this study which were designed based on commonly used clinical imaging parameters for diagnostic CT scans. The MOSkin dosimeter, designed and developed at the Centre for Medical Radiation Physics (CMRP), University of Wollongong, Australia, has previously been investigated for applications in radiation therapy (Hardcastle et al, 2008;Kwan et al, 2009) and recently in CT (Lian et al, 2012). It was found to be tissue equivalent at depth in clinical kilovoltage beams (Lian et al, 2011) and was therefore selected as our gold standard absolute dosimeter in this work.…”