DISEASE CHARACTERISTICS: Histologically proven stage I or II prostate cancer Organ confined (T1 or T2) At least 1 current positive biopsy Failed prior external beam radiotherapy for T1-T2 prostate cancer within last 18 months (with no worsening of the cancer in the first 12 months after radiotherapy) PSA nadir less than 4 ng/mL after external beam radiotherapy If prior hormonal therapy, PSA must be greater than 1.0 ng/mL and testosterone level normal after therapy Prostate volume no greater than 35 g, or 35-50 g if maximum anterior posterior diameter no greater than 2.5 cm Kattan Nomogram at least .50 60-month recurrence-free probability prior to external beam radiotherapy ASA Classification 1-3 No lymph node involvement by CT scan No metastases No prostate seroma, prostate abscess, or active prostatitis Must meet the following conditions: No artificial sphincter, penile prosthesis, or intraprostatic implant such as stent or catheter Normal rectal anatomy and rectal mucosa Rectal wall measurement no greater than 6 mm with treatment probe in place No calcification inducing a shadow in the prostate that would preclude study No significant rectal or bladder morbidity after radiotherapy (RTOG/EORTC rectal or bladder scores at least 2) No rectal fibrosis, stenosis, fistula, disease, or other rectal anomalies that would make rectal probe insertion difficult