DOSE-RESPONSE TOLERANCE OF THE VISUAL PATHWAYS AND CRANIAL NERVES OF THE CAVERNOUS SINUS TO STEREOTAXIC RADIOSURGERY

As the number of patients treated with stereotactic radiosurgery incre ases, it becomes particularly important to define with precision adver se effects on distinct structures of the nervous system. Object. This study was designed to assess the dose-response tolerance of the visual pathways and cranial nerves after exposure of the cavernous sinus to radiation. Methods. A total of 66 sites in the visual system and 210 c ranial nerves of the middle cranial fossa were investigated in 50 pati ents who had undergone gamma knife treatment for benign skull base tum ors. The mean follow-up period was 40 months (range 24-60 months). Fol low-up examinations consisted of neurological, neuroradiological, and neuroophthalmological evaluations. The actuarial incidence of optic ne uropathy was zero for patients who received a radiation dose of less t han 10 Gy, 26.7% for patients receiving a dose in the range of 10 to l ess than 15 Gy, and 77.8% for those who received doses of 15 Gy or mon (p < 0.0001). Previously impaired vision improved in 25.8% and was un changed in 51.5% of patients. No sign of neuropathy was seen in patien ts whose cranial nerves of the cavernous sinus received radiation dose s of between 5 and 30 Gy. Because tumor control appeared to have been achieved in 98% of the patients, the deterioration in visual function cannot be attributed to tumor progression. Conclusions. The structures of the visual pathways (the optic nerve, chiasm, and tract) exhibit a much higher sensitivity to single-fraction radiation than other crani al nerves, and their particular dose-response characteristics can be d efined. Ln contrast, the oculomotor and trigeminal nerves have a much higher dose tolerance.