Stereotactic Radiotherapy of Prostate Cancer With Reduction of Safety Margins

This study is testing whether reducing the safety margins used during stereotactic radiotherapy (a very precise, high-dose radiation treatment) for prostate cancer can maintain effectiveness while reducing side effects to surrounding healthy tissue, using fiducial markers (tiny implanted gold seeds) to track the prostate's exact position during treatment. **You may be eligible if...** - You are 18 or older - You have prostate cancer confirmed by biopsy (the common type, called acinar adenocarcinoma) - Your cancer is low or intermediate risk and favorable (localized, no lymph node or distant spread) - Your PSA level is 15 or below - The fiducial markers (position-tracking seeds) are placed in a suitable location as confirmed by the medical team **You may NOT be eligible if...** - Your prostate cancer is a less common type (other than acinar adenocarcinoma) - Your cancer has spread to lymph nodes or elsewhere - There is a dominant tumor at the edge of the prostate gland that may have grown through the capsule - Your PSA is above 15 - You have previously received radiation to the pelvis - The fiducial markers cannot be placed in a satisfactory position Talk to your doctor to see if this trial is right for you.