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Four cases are documented where a glioma was histologically verified in the irradiation field of a previously treated malignancy of a different cell line. Radiation-induced neoplasia in the central nervous system now has been established in the induction of meningioma and sarcoma. The association between therapeutic irradiation and glioma in the reported cases lends to the evidence that a causal relation does exist. This incidence is small and does not detract from the overall benefit of irradiation as a therapeutic modality. Cancer 58:886-894. 1986. NDUCTION OF NEOPLASIA after therapeutic irradiation I is now well e~tablished.'-~ Neoplasia of the central nervous system after radiation therapy has been documented in the form of m e n i n g i ~ m a ~-' ~ and ~ a r c o m a. ' ~-~ ' The occurrence of glial tumors has been documented less frequently in association with radiotherapy. In all reported case^^*-^^ (Table l), the causal relationship is considered, although factors such as chance occurrence of a second neoplasm, the coexistence of a second neoplasm, genetic predisposition to multiple tumors (as occurs in the phak-omatoses), or neoplastic altered immunity that renders the central nervous system more prone to oncogenic induction , and the formation of a second primary neoplasm, cannot be discounted. Recognized criteria have been established to show causal relationship between radiotherapy and the occurrence of a subsequent neoplasm.38 These include: a prolonged delay between irradiation and the detection of the second tumor, that the second tumor be in the irradiated field, that the histologic type of the second tumor be of a From the

A case of a primary malignant schwannoma of the breast is reported. This case and the review of the literature illustrate the problems of diagnosing and treating this rare malignancy.

Using an external view of the head, the ability to direct a proton radiotherapy beam at an intracerebral lesion is described, using a biostereometric (BSM) technique. The positions of markers, recognizable on computed tomography (CT) or magnetic resonance (MR) images, at known locations on the skin of a patient's head are related to the site of the lesion seen on the images. The markers' positions are determined by a BSM device, incorporating six video cameras coupled to a computer. A transformation from a coordinate system, defined by the CT or MR images, to another coordinate system, that of the BSM device, allows the proton beam to be directed towards the lesion. Markers used in this work were solid steel spheres for CT and plastic spheres containing oil for MR images.

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