Temperature steering in prostate by simultaneous transurethral and transrectal hyperthermia

Localized hyperthermia (HT) is presently under investigation as a treatment for benign prostatic hyperplasia and carcinoma of the prostate (CaP). One popular approach employs a transrectal (TR) device, a directional microwave (MW) applicator inserted into the rectum and aimed at the prostate. Alternatively, in the transurethral (TU) technique, a symmetrically radiating MW antenna is placed directly within the prostatic urethra. Used individually, TR applicators are capable of effectively heating (> 42 degrees C) the prostate up to 2 cm from the rectum, whereas TU applicators selectively heat the periurethral tissue with effective radial penetration of about 0.6 cm. Neither technique is of much value in heating the anterior prostate. In general, the highest temperatures are produced in the tissue immediately adjacent to the surface of intracavitary microwave devices. However, when MW antennas are used in arrays, the resulting heating pattern can differ significantly from that of the individual antennas. Heating at depth can be selectively enhanced and "steered" by adjusting the phase relationship between the devices. Prostatic temperature profiles were measured in 6 patients treated with TR alone, TU alone, and simultaneous TR and TU heating. In the combined treatments different phase relationships between the antennas were applied. We found that a higher temperature could be produced in the center of the prostate than on the surface of either applicator for certain phase relationships, and that the temperature profiles could be changed by shifting phase. The results of these measurements are in agreement with those of a computer simulation. Based on the above data we feel the combined use of TU and TR hyperthermia may be justified in Phase I-II trials for patients with locally advanced CaP.