PRINCIPLES OF RADIOTHERAPY OF NEOPLASTIC MENINGOSIS

Neoplastic meningosis can be a complication of a tumor originating in the brain or the meninges, or it can be a complication of a solid tumo r elsewhere that has metastasized to the leptomeninges. The therapeuti c dilemma for a radiation oncologist is that neoplastic meningosis inv olves the entire neuraxis and, as a consequence, ideally, the entire n euraxis should be radiated. However, delivering the necessary radiatio n dose to the entire neuraxis may be associated with considerable neur ologic or bone marrow toxicity. Radiotherapy of neoplastic meningosis can be performed by external beam radiation or by intrathecal injectio n of radioactive nuclides or radiolabeled monoclonal antibodies. Intra thecal radiation has the theoretical advantage that treatment is direc ted towards the entire neuraxis with limited irradiation outside the n euraxis. In practice, intrathecal radiation is still under investigati on and subject to some limitations and toxicities. Indications and tec hniques for external beam radiation may range from either therapeutic or elective cranial or craniospinal radiation to palliative involved-f ield radiation. Patients with neoplastic meningosis are frequently tre ated with a combination of radiation and chemotherapy, and/or may have been irradiated to the nervous system in the past. Both are well know n risk factors for radiation damage to the nervous system. In general, current treatment protocols focus on the development of combination c hemotherapy programs and reduction of the radiation dose to minimize t oxicity and/or to improve tumor control.