This purpose of this study is designed to compare two types of images; magnetic resonance imaging (MRI) and Trans-Rectal Ultrasound (TRUS) to see which one performs more accurately for the image-guided insertion of Fiducial Markers(FMs) within the tumour. Though effective for guiding FM placement at the poles of the prostate gland due to excellent visualization of the prostatic boundaries, TRUS may not be ideally suited for marking the GTV. Conventional TRUS is neither sufficiently sensitive nor specific for accurate visualization of intra-prostatic tumor. A new interventional MRI technique enables needle guidance to the gross tumour Volume (GTV) for FM placement. It is of particular importance that both techniques be evaluated to enable which one is more effective so that it can be implemented in the designs of future trials involving dose-escalation to prostate.

The success of dose escalation strategies in prostate cancer over the last decade has relied on high accuracy in target delineation, localization and radiation delivery. Improved biochemical control with acceptable levels of toxicity (specifically rectal) has been achieved by stringently monitoring the location of the prostate during the course of radiation treatment. Studies in the early 1990's demonstrated that daily bony alignment was a poor surrogate for prostate gland location. Since then, various strategies have been devised to localize the prostate precisely during treatment. Of these, Transrectal Ultrasound (TRUS)-guided gold fiducial marker (FM) insertion and x-ray imaging of markers has been a broadly successful approach. TRUS guidance has been used for fiducial marker insertion within the prostate since 1985 in various centers throughout the world and has also been a standard practice in PMH since 1997 in men undergoing radical external beam radiotherapy. A retrospective comparative study of 106 patients evaluating the relative accuracy of endorectal MRI and TRUS in detecting the location of tumor reported an improved performance of endorectal MRI especially in the base and midgland regions. Over the last few years, mounting experience in the interpretation of prostate MRI, and addition of physiologic imaging sequences has further improved the performance of MRI in detecting and localizing the GTV.

• Device: Transrectal APT Device or Transperineal Device will be used
• Device: TRUS probe

Inclusion Criteria:

1. ≥ 18 years old
2. ECOG status ≤ 1
3. High risk localized cancer planned for RT under FM guidance
4. Gleason > 7, PSA > 20, Clinical stage ≥ T3
5. patients(pts) must give written informed consent

Exclusion Criteria:

1. pts > 136 kg or > 60 cm in girth
2. Pts with pacemakers, cerebral aneurysm clips, shrapnel injury or devices not compatible with MRI.
3. pts with severe claustrophobia
4. pts with bleeding diathesis and anticoagulative therapy that cannot be ceased prior to needle procedures.
5. Contraindications to endorectal probe, surgically absent rectum, severe hemorrhoids or previous colorectal surgery.