A new miniature x-ray device for interstitial radiosurgery: dosimetry.

A miniature, battery operated 40 kV x-ray device has been developed for the interstitial treatment of small tumors ( < 3 cm diam) in humans. X rays are emitted from the tip of a 10 cm long, 3 mm diameter probe that is stereotactically inserted into the tumor. The beam, characterized by half-value layer (HVL), spectrum analysis, and isodose contours, behaves essentially as a point isotropic source with an effective energy of 20 keV at a depth of 10 mm in water. The absolute output from the device was measured using a parallel plate ionization chamber, modified with a platinum aperture. The dose rate in water determined from these chamber measurements was found to be nominally 150 cGy/min at a distance of 10 mm for a beam current of 40 microA and voltage of 40 kV. The dose in water falls off approximately as the third power of the distance. To date, 14 patients have been treated with this device in a phase I clinical trial.

A new miniature x-ray source for interstitial radiosurgery: device description.

A device that generates low-energy x rays at the tip of a needle-like probe was developed for stereotactic interstitial radiosurgery. Electrons from a small thermionic gun are accelerated to a final energy of up to 40 keV and directed along a 3 mm outside diameter drift tube to a thin Au target, where the beam size is approximately 0.3 mm. All high-voltage electronics are in the probe housing, connected by low-voltage cable to a battery-operated control box. X-ray output, which is nearly isotropic, consists of a bremsstrahlung spectrum and several lines between 7 and 14 keV, with characteristic radiation contributing 15% of the total energy output. To date, 14 patients with metastatic brain tumors have been treated with this device.

Initial characterization of the dosimetry and radiology 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 degree 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.

Targeted intra-operative radiotherapy (Targit): an innovative method of treatment for early breast cancer.

INTRODUCTION: We believe that conservative treatment of early breast cancer may not require radiotherapy that encompasses the whole breast. We present here the clinico-pathological basis for this view, as well as a novel therapeutic approach that allows intra-operative radiotherapy to be safely and accurately delivered to the target tissues in a standard operating theatre. THE RATIONALE: Whole-organ analysis of mastectomy specimens reveals that 80% of occult cancer foci are situated remote from the index quadrant. In contrast, over 90% of local recurrences after breast conservative therapy occur near the original tumour, even when radiotherapy is not given. Therefore, the remote occult cancer foci may be clinically irrelevant and radiotherapy to the index quadrant alone might be sufficient. A NOVEL TECHNIQUE: The Photon Radiosurgery System (PRS) is an ingenious portable electron-beam driven device that can typically deliver intra-operative doses of 5-20 Gy, respectively, to 1 cm and 0.2 cm from the tumour bed over about 22 min. The pliable breast tissue--the target--wraps around the source, providing perfect conformal radiotherapy. Being soft X-rays, the dose attenuates rapidly (alpha approximately 1/r3), reducing distant damage. RESULTS: In our pilot study of 25 patients (age 30-80 years, T = 0.42-4.0 cm), we replaced the routine post-operative tumour bed boost with targeted intra-operative radiotherapy. There have been no major complications and no patient has developed local recurrence, although the median follow-up time is short, at 24 months. CONCLUSION: It is safe and feasible to deliver targeted intraoperative radiotherapy (Targit) for early breast cancer. We have begun a randomised trial--the first of its kind--comparing Targit with conventional six-week course of radiotherapy. If proven equivalent in terms of local recurrence and cosmesis, it could eliminate the need for the usual six-week course of post-operative radiotherapy.