Prostate-Rectal Separation With PEG Hydrogel and Its Effect on Decreasing Rectal Dose

Patients who are referred to the Northern Sydney Cancer Centre for radiotherapy for treatment of their prostate cancer will be screened at the initial consultation for suitability for participation in the study. Following informed consent, those who agree to participate in the study will undergo the following procedures. Blood tests will be performed to ensure normal coagulation profile and renal function prior to any procedure. Under transrectal ultrasound guidance, patients will have insertion of fiducial gold seeds into the prostate under anaesthesia. While the patient is in theatre and under anaesthesia, the PEG hydrogel (SpaceOAR) will be inserted by Dr Thomas Eade, who will be competent in the procedure. The patient will be in the dorsal lithotomy position and prepared and draped. A transrectal ultrasound (TRUS) will be used for alignment of the needle and to ensure safe delivery. The hydrogel precursor and accelerator solutions will be mixed and connected to the Y connector that has been flushed with saline and to a syringe holder that ensures both syringe barrels are injected at the same time (comes with commercial product). The solutions will be injected within 30 minutes of mixing. After aspirating to ensure the tip of the needle is not intravascular, the perirectal space will be adequately dissected from the apex to midgland by injecting saline into the space between denonvilliers fascia and the anterior rectal space under TRUS guidance. This hydrodissection, prior to delivery of the hydrogel, should create a distance of 3-4 mm between the prostate and the rectum. Maintaining the needle position and angulation, the saline syringe is disconnected and the hydrogel system connected. After aspirating to ensure the needle tip is not in a blood vessel and under TRUS guidance, the hydrogel is injected in a smooth, continuous technique. The gel sets up within approximately 8 seconds.

In order to compare the effect of the PEG hydrogel (SpaceOAR) on the dose of radiation received by the rectum, two radiotherapy plans will be created. One planning CT scan will therefore be performed prior to the injection of the PEG hydrogel and one one week following injection of the hydrogel. The two treatment plans will be created by the same radiation therapist.

As the hydrogel is clearly visible on MRI and not on CT scans, we will obtain a pelvic MRI scan following injection of the hydrogel.. The MRI scans will be used in planning and fused to the planning CT scans to aid voluming.

Treatment:

Patients will undergo standard prostate cancer planning and treatment using image guided dose escalated IMRT as per the RNSH Department protocol and guidelines to a dose of 80Gy in 40 fractions 14.