OAR stands for "organ at risk", and in cases of prostate cancer radiotherapy treatment the rectum is the main organ at risk. The intent of this procedure is to prevent the rectum from radiation exposure during the radiotherapy aimed at the prostate.
This procedure is performed through the transperineal route under the guidance of transrectal ultrasound:
- a hydrogel is injected which is made of polyethylene glycol
- once injected, the gel solidifies and creates a space of approximately 1 cm between the rectum and prostate
- the gel stays there for three months, adequately allowing the time for delivery of radiation
- the gel then gets absorbed in three to six months' time and eliminated from the body through renal excretion