This prospective study evaluates the clinical utility of a novel real-time localization system allowing for smaller volumes of normal tissue to be included in radiation field and determines dosimetric parameters and adverse effect profiles of radiation therapy using this technology. Subjects will have beacon transponders implanted into the prostate to more precisely localize the position of the organ during radiation therapy. Hypothesis: 1. Treatment with highly targeted radiation therapy can be delivered in a daily treatment time consistent with routine clinical practice. 2. Highly targeted radiation therapy with reduced PTV margin will result in a significant decrease in rectal and bladder volume treated.

This study will seek to establish the clinical feasibility of a novel real-time localization and tracking system for use of reduced PTV margins during intensity modulated radiation therapy (IMRT), which will allow treatment of smaller volumes of normal tissue during radiation therapy. Such a reduction in the PTV margins and the exposure of healthy tissue during treatment may allow for several future improvements in prostate radiotherapy including:

• decreased acute and chronic adverse effects with similar local tumor control
• dose escalation to achieve higher cure rates with similar adverse effects to standard dose treatment
• hypofractionation to shorten the time of, and lower the expense of, treatment without increased adverse effects.

Inclusion Criteria:

• Histologically confirmed adenocarcinoma of the prostate
• Low Risk: T1a, T1b, T1c, T2a; Gleason Score less than 7, PSA less than or equal to 10
• Intermediate Risk: T2b, T2c; Gleason Score less than or equal to 7, PSA less than or equal to 15
• Ability to comply with study schedule
• Age 40 or older
• Zubrod PS 0 or 1
• Signed informed consent

Exclusion Criteria:

• Node positive or metastatic prostate cancer
• Prior treatment of prostate cancer with surgery, chemotherapy, cryotherapy or brachytherapy
• History of prior pelvic radiotherapy
• History of abdominoperineal resection
• History of HIV infection
• History of chronic prostatitis or chronic cystitis
• History of bleeding disorder or any active anticoagulation (excluding ASA)
• PT or INR outside normal range for institution
• Active implanted devices such as cardiac pacemakers and automatic defibrillators.
• Prosthetic implants in the pelvic region that contain metal or conductive materials (eg., an artificial hip).
• Patients with maximum anterior-posterior separation through the torso minus the height of the center of the prostate greater than 17 cm (technical reason for Calypso System, see appendix 8).
• Prior history of androgen deprivation therapy has been deleted and these patients are allowed on study.

Patients with localized prostate cancer for whom definitive radiation therapy is planned to the prostate only or prostate and seminal vesicle only, without ajuvant or neoadjuvant hormornal therpy will be referred by the radiation oncololgists and urologists.