Radiotherapy for optic nerve sheath meningioma: a case for earlier intervention?
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AIMS: To assess tumour control, visual outcomes and toxicity after radiotherapy for all patients with optic nerve sheath meningiomas (ONSM) treated by a single radiation oncologist at a single institution over a 15 year period. To explore potential predictors of outcomes. MATERIALS AND METHODS: All patients underwent ophthalmological and radiological assessments before radiotherapy. These were repeated at regular intervals after treatment. A retrospective analysis of clinical, dosimetric and radiological data was carried out. Patients with useful vision before radiotherapy were divided into two groups - those with maintained or improved vision and those with a deterioration in vision. The groups were compared using the Mann-Whitney U-test with regard to eight potential predictors of outcome. RESULTS: Seventeen patients with 18 ONSM were treated with fractionated radiotherapy (46.8-55.8 Gy in 26-31 fractions). No evaluable tumours grew after treatment: control rate 100% (95% confidence interval 82-100%). Using the most common definition of visual function described in the literature, vision was maintained or improved in 89% (95% confidence interval 67-97%) of cases. In those with useful vision before treatment (13 evaluable eyes), visual acuity was maintained or improved in eight (62%, 95% confidence interval 36-82%). There was a suggestion that the time from the onset of symptoms to radiotherapy may influence outcome. Those with stable or better visual acuity after radiotherapy had been observed for a shorter time compared with those who had worse visual acuity (median of 18 months versus 62 months). Acute and late toxicity from radiotherapy was manageable. CONCLUSION: Radiotherapy is an extremely effective modality in arresting the growth of ONSM. A longer time from symptom onset to the start of radiotherapy may predict for poorer outcomes.
