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 tumor elsewhere that has metastasized to the leptomeninges. The therapeutic dilemma for a radiation oncologist is that neoplastic meningosis involves the entire neuraxis and, as a consequence, ideally, the entire neuraxis should be radiated. However, delivering the necessary radiation dose to the entire neuraxis may be associated with considerable neurologic or bone marrow toxicity. Radiotherapy of neoplastic meningosis can be performed by external beam radiation or by intrathecal injection of radioactive nuclides or radiolabeled monoclonal antibodies. Intrathecal radiation has the theoretical advantage that treatment is directed towards the entire neuraxis with limited irradiation outside the neuraxis. In practice, intrathecal radiation is still under investigation and subject to some limitations and toxicities. Indications and techniques for external beam radiation may range from either therapeutic or elective cranial or craniospinal radiation to palliative involved-field radiation. Patients with neoplastic meningosis are frequently treated with a combination of radiation and chemotherapy, and/or may have been irradiated to the nervous system in the past. Both are well known risk factors for radiation damage to the nervous system. In general, current treatment protocols focus on the development of combination chemotherapy programs and reduction of the radiation dose to minimize toxicity and/or to improve tumor control.