An evaluation of contouring and planning methods to expand the role of SBRT with CyberKnife in the treatment of localised prostate and renal cancers

Abstract

Technological advancement has led to the substantial evolution of stereotactic body radiotherapy (SBRT). The CyberKnife SBRT platform achieves a high degree of precision through robotic delivery of multiple non-coplanar beams, combined with intrafraction motion compensation to submillimetre accuracy. This enables tumour dose escalation while limiting dose to normal tissues, although any benefit is largely dependent on the quality of contouring and planning processes. The newly developed multi-leaf collimator (MLC) improves CyberKnife delivery by reducing treatment time and has the potential to treat large, complex tumour more effectively. A large body of data supports the use of SBRT in early prostate cancer and randomised trial data from the PACE-B trial demonstrates rates of acute toxicity to be equivalent to standard radiotherapy. The evidence in high-risk prostate cancer is limited and is being addressed in the PACE-C trial. This thesis investigates methods of improving SBRT quality in early prostate cancer and evaluates its application in high-risk prostate cancer and primary renal cancer. Pending long-term randomised trial data, I report 5-year outcomes from the first UK prostate CyberKnife cohort, involving 62 patients treated at a single centre. I then explore the impact of prostate volume and dosimetry on toxicity and consider preventative strategies. To ensure the quality of clinical outlining I evaluate interobserver variability within the PACE trial quality assurance programme, and develop a more consistent method for seminal vesicle (SV) delineation for use in PACE-C. To expand the utility of SBRT to higher risk prostate cancer patients, I explore the feasibility of CyberKnife planning for larger target volumes with a greater proportion of SV and test the benefit of using MLC in this setting. I will begin the assess the wider applicability of MLC in urological malignancy by comparing with the Iris variable collimator in SBRT planning for primary renal cancer.