Cryotherapy for the prostate: an in vitro and clinical study of two new developments; advanced cryoneedles and a temperature monitoring system.

OBJECTIVES

To assess the characteristics of two new developments in cryotherapy for the prostate, IceRods (Oncura, Amersham, UK; 17 G cryoneedles with an advanced heat exchanger which produces a precise ice-ball comparable in size to those with larger diameter cryoneedles) and the Multitemp 1601 temperature monitoring system (TMS, InvivoSense, Trondheim, Norway) probes, in an in vitro model and in a clinical setting, to assess their usefulness, focusing in particular on the TMS probes.

PATIENTS, MATERIALS AND METHODS: We assessed the temperature profile and performance of the IceRods in several different configurations, in conjunction with the TMS probes for temperature mapping, in a phantom prostate model. Subsequently 20 patients with prostate cancer were treated with cryosurgery either as a primary or secondary treatment for radiation failure; all had a standard treatment protocol. The temperatures throughout the procedure were recorded accurately and analysed. RESULTS The IceRods were better able to freeze tissue, reaching lower temperatures than conventional cryoneedles. The IceRods were also capable of forming ice-balls with a maximum diameter of >6 cm after freezing at full power for 10 min. The TMS probes depicted real-time temperature gradients over either four or eight points in a linear array, enabling more thorough monitoring of the temperature changes during a treatment cycle. In the clinical setting, in all 20 patients, therapeutic freezing of <-40 degrees C was achieved in both the cycles. Temperatures of approximately - 40 degrees C were attained in the area just outside the prostate, as measured by the TMS probes, but with variation along the longitudinal axis. The rectal and external urinary sphincter temperatures did not fall below 0 degrees C at any of the points along the eight-point temperature probe, but there was variation in temperature along the prostate.

CONCLUSION

IceRods and the TMS probes are clinically useful, requiring fewer cryoneedles and with more efficient temperature monitoring; this would be expected to reduce morbidity and increase safety without compromising an adequate oncological outcome. The IceRods were useful in larger prostates of >3.5 cm long, which obviated the need for a 'pull-back' technique. The TMS probes showed convincingly the variation in temperatures along one line, suggesting that single-point temperature monitoring might not accurately depict the lowest temperatures reached during treatment, which is particularly important in the rectum. This is a significant development in cryosurgery and would make the procedure safer, reproducible and allow interested clinicians to learn the technique safely and more quickly.