THE CANADIAN JOURNAL OF NEUROLOGICAL SCIENCES Interstitial Irradiation of Skull Base Tumours

The rationale for interstitial irradiation of tumours in and around the skull base is reviewed, and the experience accumulated with pituitary adenomas, meningiomas, and chordomas is summarized. Intracystic irradiation for craniopharyngiomas is also reviewed. RESUME: Irradiation interstitielle des tumeurs de la base du crane Nous passons en revue la raison d'etre de 1'irradiation interstitielle des tumeurs de la base du crane ainsi que notre experience avec les adenomes pituitaires, les m^ningiomes et les chordomes. Nous discutons aussi de 1'emploi de 1'irradiation intracy ste dans le craniophary ngiome. Can. J. Neurol. Sci. 1985; 12:366-370 The majority of meningiomas, acoustic schwannomas, and pituitary adenomas are extra-arachnoid, histologically low grade neoplasms which can be totally extirpated using microsurgical techniques. A certain number, however, because of size, location, and/or invasive biological behaviour are not amenable to gross total removal. The surgical curability of craniopharyngiomas remains controversial, and chordomas, although rare tumours, can seldom if ever be totally removed in spite of innovative and aggressive surgical procedures. Optimal surgical resection remains the initial treatment of choice for most tumours arising in and around the skull base. There is increasing evidence that adjuvant therapy with radiation can prevent or delay the recurrence of incompletely resected meningiomas," chordomas," and craniopharyngiomas.'" For pituitary adenomas, external beam irradiation has long been recognized to be an effective adjunct to subtotal resection.' Excellent results have been obtained with irradiation in cases of endocrine-inactive pituitary adenomas ', prolactinomas,''' Cushing's disease, and acromegaly. A number of different radiation techniques have been utilized in treating pituitary adenomas, including parallel opposed fields, three-field techniques, and arc rotational therapy. The relative radioresistance of slow-growing, mitotically inactive neoplasms such as meningioma, chordoma, craniopharyngioma and schwannoma underscores the need for high tumour radiation doses in order to achieve maximum benefit. However, the brain's tolerance to radiation is finite, and the cure or sterilization of any tumour (malignant or low-grade) is beyond the capability of any radiation modality that affects not only the tumour but also adjacent brain and blood vessels. We must therefore attempt to improve upon conventional teletherapy, which cannot deliver the ionizing radiation in a sufficiently well focused volume to affect only the tumour and spare the brain. There are a number of ways of improving the therapeutic ratio between tumour and surrounding brain: 1) focused gamma radiation from numerous narrow radiation beams that are stereotactically directed to a small target volume, 2) accelerated charged particles which can be focused precisely using the Bragg peak technique, and 3) implantation of radiation sources within a tumour volume (i.e. interstitial brachytherapy). In this paper, we review the experience with interstitial radiation in the treatment of pituitary adenomas, meningiomas, and chordomas, and intracystic irradiation of craniopharyngiomas.