Charged-particle radiosurgery of the brain.

Charged-particle beams (e.g., protons and helium, carbon and neon ions) manifest unique physical properties which offer advantages for neurosurgery and neuroscience research. The beams have Bragg ionization peaks at depth in tissues, and finite range and are readily collimated to any desired cross-sectional size and shape by metal apertures. Since 1954 nearly 6000 neurosurgical patients worldwide have been treated with stereotactic charged-particle radiosurgery of the brain for various localized and systemic malignant and nonmalignant disorders. Experimental studies with charged-particle beams have been carried out in laboratory animals to characterize anatomic and physiologic correlates of various behavioral and functional properties in the brain. Highly focused charged-particle beams have been used to induce sharply delineated laminar lesions or discrete focal ablation of deep-seated brain structures for the study of the functional anatomy of selected intracranial sites. Charged-particle beam irradiation for stereotactic radiosurgery and radiation oncology of intracranial disorders has achieved increasing importance internationally. More than 30 biomedical accelerator facilities on four continents are currently fully operational, under construction, or in an active planning stage; this last group consists primarily of dedicated biomedical hospital-based facilities. Therapeutic efficacy has been demonstrated clearly for the treatment of selected intracranial sites, e.g., pituitary adenomas and intracranial arteriovenous malformations. Heavier charged particles (e.g., carbon and neon ions) have been found to manifest a number of valuable radiobiologic properties and appear to be of potential advantage in the radiosurgical treatment of those primary or metastatic brain tumors that are radioresistant. The optimal dose and choice of charged-particle species must be determined for the treatment of the different intracranial disorders to improve the cure rate and to minimize potential adverse sequelae of the reaction of the brain to radiation injury.