The Prostatron antenna was found to be a monopole design consisting of a coaxial cable with a 3.3-cm length of inner conductor exposed at the tip. The
Targis antenna was observed to be a dipole design with a 2.8-cm helical coil attached through a ground connection and a tap point to a coaxial cable. The heating pattern of the
Targis antenna was symmetric; that of the Prostatron was asymmetric with substantial back heating along the
catheter axis in the direction of the microwave
power source. The mean extension of the 30 degrees C isotherm in the direction of the
power source with the Prostatron antenna (71.5 mm; 95% confidence interval [CI], 63.4 to 79.6 mm) was 55% greater (P < 0.0005) than that with the
Targis antenna (46.0 mm; 95% CI, 38.2 to 53.8 mm). Return loss with the
Targis antenna declined sharply to a relative minimum value of -32.9 dB (95% CI, -73.8 to 8.0 dB) at 915 MHz, providing evidence of this antenna's capacity for impedance matching; little change was observed with the Prostatron in return loss over a frequency range 100 MHz above and below this antenna's standard operating frequency of 1296 MHz. The mean reflected power of the
Targis antenna (0.4%; 95% CI, 0.0% to 1.4%) was lower by more than 20-fold (P = 0.036) than that of the Prostatron antenna (11.0%; 95% CI, 3.4% to 18.7%); thus, the potential for efficient operation was greater with the
Targis than the Prostatron antenna.
CONCLUSIONS: The
Targis microwave antenna was found to provide a more targeted heating pattern and have a capacity for more efficient thermal energy delivery than the Prostatron antenna. These differences observed in vitro could potentially translate into clinical advantages in vivo, such as improved tolerability of microwave treatment, reduced risk of complications, greater thermoablative efficacy, and scalability.