Experimental Dose Effects After Permanent and Temporary Interstitial Irradiation of the Brain

Abstract

Clinical experience has demonstrated that gliomas of the brain are relatively resistant to conventional irradiation (teletherapy) (Bloom and Walsh 1975; Burger et al. 1979; Leibel and Sheline 1987). Thus, the dose-effect curve for tumor control and the tissue damage curve obtained in many clinical situations turn out to be almost identical. This has led to various attempts to increase the therapeutic spectrum of radiotherapy. Apart from the stereotaxic focusing of radiation with linear accelerators, brachytherapy has been receiving a considerable amount of attention again in the past few years (Bernstein and Gutin 1981; Gutin and Leibel 1985; Ostertag 1986). The dose rates used for interstitial radiation vary from very high dose rates for different afterloading techniques to very low dose rates for permanent implants with low-energy emitters such as iodine 125. The dosimetry calculations for interstitial irradiation have been based largely on clinical experience (Anderson et al. 1981; Hilaris 1975). To devitalize a tumor with high local radiation doses no longer poses as serious a problem as the damage done to the tumor-free tissue. This damage is not so much the harm inflicted by direct radiation but rather that caused by secondary chronic vasogenic edema. In order to obtain confirmed biological data as a foundation on which to base the clinical dosimetry, we studied the effects of doses delivered through γ-emitters with different energy and dose rates.