CRYOSURGICAL INSTRUMENTATION AND DEPTH DOSE MONITORING

The equipment needed for cutaneous cryosurgery is dependent upon the type of lesions to be treated, the frequency of its use, and the dermatologist's expertise in cryosurgery. If the physician wishes occasionally to treat an actinic keratosis or verruca, a small carbon dioxide kit for making CO2 pencils is adequate. (Fig. 5-1). Should a liquid nitrogen source be accessible a small "Thermos" plus cotton swabs will be sufficient (Fig. 5-2). To this might be added Zacarian copper discs (Fig. 5-3) for emersion in the nitrogen for cryoprobe application. For dermatologists wishing to treat many lesions, particularly malignant lesions, an in-office supply of liquid nitrogen and an apparatus to utilize the nitrogen in spray or cryoprobe mode are essential. Hand-held instruments are the most popular, but table-top and hospital-type units are available. For malignant lesions, depth dose monitoring equipment is also necessary. The standard equipment consists of a pyrometer-thermocouple device. Vacuum insulated liquid nitrogen storage dewars can be purchased from the manufacturer, from cryosurgical instrument companies (Frigitronics, Brymill, Tower, Gilmore, etc.) or from the welding supply companies which may deliver the liquid nitrogen. These companies may rent the dewars in various sizes. The 10-liter unit is convenient if office delivery of liquid nitrogen is not available and the physician or his assistant has to transport it from a hospital or some other source. If office delivery is possible, the most practical dewars are in the 25-35 1 range. These units have static holding time from 3 weeks to 3 months, allowing infrequent filling (usually at 2-6-week intervals). The more expensive the unit the longer the static holding time, and consequently, the cheaper the cost of keeping a nitrogen supply on hand. A rocker base for pouring (Fig. 5-4A) can be used for transfer of the nitrogen from the storage dewar to the treatment unit, but a dispenser top (Fig. 5-4B) is superior. These can be purchased from the same sources that furnish the dewar. © 1990.