Initial characterization of the dosimetry and radiobiology of a device for administering interstitial stereotactic radiosurgery

OBJECTIVE: We report the design and initial characterization of the dosimetry and radiobiology of a novel device for interstitial stereotactic radiosurgery. INSTRUMENTATION: The device is lightweight, handheld, and battery-powered, and it emits x-ray radiation from the tip of a probe 3 mm in diameter by 10 cm in length. METHODS: The dosimetry was characterized by two independent methods: thermoluminescent dosimeters and radiochromic film. The radiobiology was characterized by in vivo irradiation of rat liver, dog liver, and dog brain. The animals were killed at varying intervals of time, and histological examinations were performed. Heat transfer from the probe to dog brain was studied in vivo by placing thermocouple sensors around the probe tip before irradiating. RESULTS: Both dosimetric methods showed a steep dose-distance fall-off relationship (proportional to the reciprocal of the cube of the distance from the probe tip). Rats and dogs that were killed weeks to months after liver irradiation tended to have sharply demarcated lesions. Liver enzyme levels, measured serially in the dogs, did not give evidence of chronic inflammation. Histological examination of the brains of dogs that were killed acutely after irradiation did not show evidence of inflammation, edema, or hemorrhage. The tissue temperature elevation 1 cm from the tip never exceeded 0.5 degrees C, thereby excluding hyperthermia as a significant contributor to the formation of lesions. CONCLUSIONS: Because this device requires relatively few supporting resources, has sharp dosimetric properties, and seems to be safe, it may be useful as a clinical tool for interstitial stereotactic radiosurgery.