A sterile, bioabsorbable material (e.g., liquid or gel) intended to be injected between the prostate and the rectum prior to radiotherapy of the prostate, to increase the distance between the prostate and the anterior rectal wall, thereby reducing exposure of the rectum to radiation. It is typically comprised of hyaluronic acid (HA) and may be available in a prefilled syringe. This is a single-use device.