PubMed · 5205185
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D Firth. 1971. Cold as an adjunctive modality.. https://pubmed.ncbi.nlm.nih.gov/5205185/
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BACKGROUND AND OBJECTIVES: During liver cryosurgical procedures, the authors observed seriously inconsistent rates of iceball growth implying inconsistent probe cooling rates. This inconsistency can lead to several problems, most importantly, loss of precision and reliability in freezing the chosen volume of tissue. The observation led to investigation of the performance of the cryosurgery machine. METHODS: The performance of the Cryotech LCS 3000 with different moratorium periods was investigated. Freezing was performed in a gelatin phantom with thermocouple monitoring at the probe tip. RESULTS: It was determined that a moratorium period between unit filling and clinical use essentially eliminates the uncertainty in probe performance. The need for this arises from the design of the system. A full liquid nitrogen tank does not have the necessary pressure required to induce effective freezing. A partially filled tank increases vapor pressure in the storage dewar driving more liquid nitrogen through the probes, thus allowing a more reliable and faster freeze. CONCLUSION: The simple measure of introducing a moratorium period between filling the dewar with liquid nitrogen and its use in surgery allows partial evaporation of the nitrogen and enhances cryoprobe performance. This protocol modification may reduce the chance of inconsistent probe performance thus making liver cryosurgery more reliable.
This study presents the design and characterization of an insulating probe made of silicone that could be used for enhancing the safety and efficacy of prostate cryosurgery. The probe would be placed in Denonvilliers' fascia between the prostate and the rectum prior to freezing. During freezing, the iceball would be monitored by ultrasound through the silicone, and direct temperature monitoring of the rectal and prostatic tissue via thermocouples mounted on opposing sides of the device. Both theoretical and experimental studies were performed to verify the insulating and acoustic properties of the probe. The insulating effect of the silicone will enhance cell death within the prostate while minimizing tissue freezing injury and therefore fistula formation postfreeze in the rectum. Experiments were also performed with the insulator placed in gelatine which showed that the silicone material is transparent to ultrasound. In addition the silicone was itself visible under ultrasound imaging, a characteristic which may assist in the delivery of the device to the surgical site. One possible scenario for reconfiguration and delivery of the device is suggested prior to a cryosurgery. The success of this device in insulating and monitoring temperature during freezing suggests that it can also be useful in protecting sensitive tissues adjacent to a surgical site when extreme heat is applied (i.e., electron or hyperthermic surgery).
The technological advances which have caused renewed interest in cryosurgery are the development of intraoperative ultrasound to monitor the therapeutic process and the development of new cryosurgical equipment designed to use supercooled liquid nitrogen. The thin, highly efficient probes, available in several sizes, can be placed in diseased sites via endoscopy or percutaneously in minimally invasive procedures. The manner of use is to place the probe in the desired location in the diseased tissue with ultrasound guidance. If required by the size or location of the tumor, as many as five probes can be inserted and cooled to -195 degrees C simultaneously. The process of freezing is monitored by ultrasound which displays a hypoechoic (dark) image when the tissue if frozen. Rapid freezing, slow thawing, and repetition of the freeze/thaw cycle are standard features of technique. Clinical applications which have become common in the past 4 years include the treatment of prostatic cancer and liver tumors. The cases selected for cryosurgery are generally those for which no conventional treatment is possible. However, especially in prostatic cancer, the operative morbidity is so low and the results of therapy are sufficiently good in the short term to merit consideration of use in earlier stages of the disease. Diverse tumors in other sites, such as the brain, bronchus, bone, pancreas, kidney, and uterus, have also been treated in small numbers by cryosurgery. Judging from this experience, further expansion in the use of cryosurgical techniques seems certain.