Interstitial microwave thermal therapy for prostate cancer: Method of treatment and results of a phase I/II trial

Purpose: Interstitial microwave thermal therapy is experimental treatment f or prostate cancer with the goal of curing disease, while causing fewer com plications than standard treatment options. We present a method for deliver ing interstitial microwave thermal therapy using microwave radiating helica l antennae inserted percutaneously under transrectal ultrasound guidance. W e report the results of a trial of this method in 25 patients in whom prima ry external beam radiation therapy had previously failed. This patient grou p currently has limited curative options that are associated with a high co mplication rate. However, these recurrent tumors often remain localized to the prostate, and so they may be amenable to localized therapy. Materials and Methods: Patients with proved prostatic adenocarcinoma were c andidates for treatment when prostate specific antigen (PSA) was 15 ng./ml. or less and prostate volume was 50 cc. or less. Followup included PSA meas urement, digital rectal examination, urinalysis, and documentation of adver se events at 4, 8, 12 and 24 weeks. Sextant biopsy was performed at week 24 . The procedure involved the insertion of 5 antennae percutaneously through a modified brachytherapy template. The antenna arrangement was determined based on computer simulated predictions of temperature throughout the prost ate. The prostate was dissected away from the rectum by an injection of ste rile saline to provide a thermal barrier that protected the rectum from the rmal damage. Temperatures were monitored using interstitial mapping thermis tor probes that were also inserted through the template. A minimum peripher al target temperature of 55C but less than 70C was maintained for 15 to 20 minutes, while the urethra, rectum and hydrodissection space remained below 42C. The urethra and rectum were actively cooled in addition to hydrodisse ction. Results: Peripheral target temperatures of 55C were achieved. The urethra a nd rectum remained at a safe temperature. The procedure, including setup an d treatment, required approximately 2.5 hours of operating room time. At 24 weeks the PSA nadir was 0.5 ng./ml. or less in 52% of patients and 0.51 to 4 ng./ml. was achieved in an additional 40%. The negative biopsy rate at 2 4 weeks was 64%, assuming that 3 patients lost to followup would have had p ositive results. No major complications were observed and in most cases min or complications resolved within 3 months. Conclusions: Interstitial microwave thermal therapy for prostate cancer was developed to heat the prostate safely to a cytotoxic temperature. Experien ce with 25 patients in whom external beam radiation therapy for prostate ca ncer had failed indicates that the treatment is safe. Although our series i ndicates that this therapy may be effective, further studies and longer fol lowup are required in larger patient groups to confirm the potential role o f this therapy as an option for recurrent and primary prostate cancer.