Focal Radiotherapy for Previously Treated Prostate Cancer Patients

Participants must have biopsy proven locally recurrent prostate cancer. Biopsy will be performed by a Urologist. Participants will have PSMA-PET (prostate-specific membrane antigen and positron emission tomography) scan and MRI in Radiology and Nuclear Medicine by experienced Radiologists in the Royal North Shore Hospital. before starting stereotactic radiotherapy. Participants will require fiducial markers inserted in the prostate and may require hydrogel insertion depending on the location of the recurrence. If these are required, it will be done by experienced radiation oncologists. Fiducial markers insertion involves inserting three gold markers into the prostate. It will be used to locate the prostate accurately during radiation treatment. Hydrogel is a temporary gel being injected into the space between the prostate and rectum to reduce the dose of radiation received by the rectum to minimise side effects from the treatment, Focal Stereotactic Body treatment (SBRT) will be used in the study. There are three groups of participants. Each group will receive different level of radiation dose to test the safety of increasing radiation dose. Group 1 will receive 36 grays (radiation dose unit, Gy)) in 6 treatments. Group 2 will receive 38 grays in 6 treatments and Group 3 will receive 40 grays in 6 treatments. The incremental dose escalation will cease if any excess acute toxicity or late grade 3 toxicity. SBRT will be delivered two to three times per week, every second day. The number of treatments per week will depend on the day of the week participants start their treatment. Participants will be reviewed weekly or second weekly. Toxicity will be recorded. A Safety Committee will be formed containing multi-disciplinary team members. All serious adverse events will be reported to the Principal Investigator and Human Research Ethics Committee within 24 hours.

Inclusion criteria

• Men > 4yrs from external beam radiotherapy (EBRT) meeting the Phoenix definition of biochemical failure or men > 5yrs from EBRT if neo-adjuvant and/or adjuvant androgen deprivation therapy (ADT) also used
• Recurrence localised to less than 1 lobe of prostate on both PMSA and multi-parametric MRI (less than equal to cT2a)
• Recurrence must be biopsy proven, with positive biopsies limited to the PET and MRI suspicious region.
• Life expectancy at least 10yrs from time of SBRT
• PSA < 10

Exclusion criteria

• Recurrence in immediate proximity to rectum (unless able to have hydrogel)
• Grade 3 or more toxicity from previous EBRT
• Contra-indicated for fiducial insertion
• GS 8,9 or 10 disease previously (relative - consider if decent disease free interval)