This is an observational study to collect placement and tracking data for patients who have the Calypso transponders implanted into the peri-prostatic tissue.

Use of Real-time tracking using Calypso Electromagnetic Beacons in the prostatic bed of patients receiving radiotherapy following radical prostatectomy.

Inclusion Criteria:

1. Patients with recurrence of prostate cancer following radical prostatectomy for prostate adenocarcinoma
2. Patients with initially undetectable PSA following prostatectomy for prostate adenocarcinoma with subsequent PSA relapse
3. Patients being planned for radiation therapy
4. Patient is being planned for implant with Calypso Transponders in the prostate bed
5. No evidence of distant metastases
6. Age ≥ 18 years
7. Informed consent

Exclusion Criteria:

1. The patient has received other investigational therapy in the last 60 days
2. The patient has previously been implanted with permanent beacon transponders
3. The patient has a prosthetic implant in the pelvic region that contain metal or conductive materials
4. The patient has any other medical or other condition that would, in the investigator's opinion, make them a poor candidate for the study

Patients with cancer of the peri-prostatic tissue or prostate bed