Ultrasound imaging in radiotherapy and dosimetric quantification with Monte Carlo techniques

Abstract

This thesis considered the use of ultrasound-based image guidance systems, employed to account for internal motion of the prostate gland during radiotherapy. A clinical evaluation of the Clarity soft tissue visualisation system, employed at Galway University Hospital during patient set-up, was performed based on a retrospective statistical analysis of clinically obtained prostate motion data. Results obtained indicated that there were no clinically significant systematic errors within the manufacturer recommended system workflow and agreed well with previously published studies. The Autoscan ultrasound probe, which is clinically employed at the Institute of Cancer Research, London, UK, was also considered in this work. This probe remains in place during treatment delivery, tracking the prostate in real-time. Characterisation of the effect of the probe on the local dose distribution was performed, by Monte Carlo means, which have been shown to be the most accurate method of modelling absorbed dose. To achieve this aim, an accurate Monte Carlo model of a clinical linear accelerator was developed (agreeing with measurement within a clinically acceptable level). The dose perturbation characterised in this study can now be considered during treatment planning, when using the Autoscan ultrasound probe for prostate motion estimation.