Andrew Howie

Measurement of rectal dose during HDR brachytherapy using the new MOSkin dosimeter

In HDR prostate brachytherapy, post-treatment complications occur due to overdosing the rectum wall and urethra. An area of concern regarding treatment is related to how the rectal wall dose is calculated using treatment planning systems. Treatment planning systems can calculate the dose delivered to the rectal wall, assuming that the rectum is filled with water equivalent material. This assumption is not always correct, as the rectum is emptied before treatment begins. The aim of this research is to quantify the difference in the dose measured in an ‘empty’ rectal phantom, and in a rectal phantom filled with water equivalent material. Results indicate that the dose measured by the MOSkin and RadFET in an empty rectum is approximately 10–15% lower than the dose measured dose in a full rectum, and the dose calculated by the PLATO TPS, which assumes that the rectum is full. This could have implications on the design of HDR treatment plans.

HDR brachytherapy in vivo source position verification using a 2D diode array: A Monte Carlo study

Abstract Purpose This study aims to assess the accuracy of source position verification during high‐dose rate (HDR) prostate brachytherapy using a novel, in‐house developed two‐dimensional (2D) diode array (the Magic Plate), embedded exactly below the patient within a carbon fiber couch. The effect of tissue inhomogeneities on source localization accuracy is examined. Method Monte Carlo (MC) simulations of 12 source positions from a HDR prostate brachytherapy treatment were performed using the Geant4 toolkit. An Ir‐192 Flexisource (Isodose Control, Veenendaal, the Netherlands) was simulated inside a voxelized patient geometry, and the dose deposited in each detector of the Magic Plate evaluated. The dose deposited in each detector was then used to localize the source position using a proprietary reconstruction algorithm. Results The accuracy of source position verification using the Magic Plate embedded in the patient couch was found to be affected by the tissue inhomogeneities within the patient, with an average difference of 2.1 ± 0.8 mm (k = 1) between the Magic Plate predicted and known source positions. Recalculation of the simulations with all voxels assigned a density of water improved this verification accuracy to within 1 mm. Conclusion Source position verification using the Magic Plate during a HDR prostate brachytherapy treatment was examined using MC simulations. In a homogenous geometry (water), the Magic Plate was able to localize the source to within 1 mm, however, the verification accuracy was negatively affected by inhomogeneities; this can be corrected for by using density information obtained from CT, making the proposed tool attractive for use as a real‐time in vivo quality assurance (QA) device in HDR brachytherapy for prostate cancer.

A risk-based approach to development of ultrasound-based high-dose-rate prostate brachytherapy quality management

PURPOSE The purpose of this study was to apply a risk-based approach to the development of a quality management (QM) program for ultrasound-based high-dose-rate (HDR) prostate brachytherapy (pBT) treatment planning and delivery. METHODS AND MATERIALS A QM program was developed by a multidisciplinary team, using both an in-house risk-and-benefit balance impact template (RABBIT) tool and a failure modes and effect analysis (FMEA). FMEA scores were determined by three physicists, one radiation therapist and two radiation oncologists who were familiar with the protocol. The QM program produced by both risk-based techniques was then compared and consolidated. RESULTS The RABBIT tool identified 26 potential risks during the treatment planning and delivery process. During the FMEA, a total of 35 potential failure modes were identified from the seven major processes in ultrasound-based HDR pBT. For the 35 potential failure modes, risk priority number scores ranged from 14 to 267. The highest ranked failure mode was identified to be mislabeling/connection of the transfer tubes/catheters. From the risks analyses, a comprehensive QM program was developed. CONCLUSION Both the RABBIT tool and process mapping and FMEA were shown to be valuable tools in developing a QM program for ultrasound-based HDR pBT treatments. A considerable number of the potential failure modes identified in both tools were related to human or procedural errors, highlighting the importance of checklists and protocols in delivering a safe and effective ultrasound-based HDR pBT treatment.