Stereotactic Ablative Radiation (SABR/SBRT) will be prescribed to a dose of 35 Gy in 5 fractions, once weekly to prostate with a simultaneous intra-prostatic boost to the MR detected nodule up to 50Gy. The pelvic lymph nodes and seminal vesicles will also receive 25 Gy in 5 weekly fractions.

Inclusion Criteria:

• Histologically confirmed prostate adenocarcinoma
• High-risk prostate cancer, defined as at least one of: T3, Gleason 8-10, OR PSA > 20 ng/mL
• Willing to give informed consent to participate in this clinical trial

Exclusion Criteria:

• Prior pelvic radiotherapy
• Contraindication to radical prostate radiotherapy e.g. connective tissue disease or inflammatory bowel disease
• Contraindication to prostate MRI
• No evidence of castrate resistance (defined as PSA < 3 ng/ml while testosterone is < 0.7nmol/l. Patients could have been on combined androgen blockade but are excluded if this was started due to PSA progression.
• Definitive extrapelvic nodal or distant metastatic disease on staging investigations.