Interstitial microwave hyperthermia for brain tumors

Abstract

The technical feasibility and clinical safety of interstitial microwave hyperthermia was evaluated in six patients with glioblastoma and malignant astrocytoma. Prior to entry into the study, each patient had received surgery, radiation and nitrosourea chemotherapy. All patients were implanted at open craniotomy with a flexible microwave radiator/sensor (o.d. 1.5 mm) and transcutaneously connected to a 2450 MHz microwave generator. Intraoperative thermal field plots and cooling curves were obtained with the aid of non-perturbing probes (o.d. 1.2 mm) perpendicularly driven into the tumor at fixed radial distances from the central antenna. In comparison to similar measurements carried out in normal feline brains, human gliomas were unable to efficiently dissipate heat as demonstrated by doubling of the effective diameter of the thermal field to 4 cm and by prolongation of the decay time in all cooling curves. Patients were also implanted with subarachnoid ICP monitors over the contralateral hemisphere. Two postoperative treatments were given at 45°C for 60 min on the night of surgery and 48 hr later. No patient was aware of power on/ power off, there were no permanent neurologic sequelae and there were no significant changes in the ICP. Power was manually controlled with visual feedback in the first three patients and automatically controlled by a computer-based system in the final three patients. Four of the six patients have lived 18 months after implantation and two of these have negative CT scans at 18 and 27 months since recurrence. It appears that interstitial microwave hyperthermia is both feasible and safe within the intracranial cavity and that combined interstitial irradiation and hyperthermia deserves clinical study.