The role of radiotherapy in the management of low grade glioma of the visual pathway in children

Abstract

Background: Treatment of low grade glioma of the visual pathway in children poses a challenge to the neuro-ophthalmologist and radio-oncologist owing to their low incidence and the lack of consensus about ‘optimal’ treatments. Objectives: To define the role of radiotherapy in present and future treatment approaches. Methods: Reports in the literature spanning 60 years of radiation therapy, including orthovoltage, megavoltage, and recent modern high-precision treatment techniques, were reviewed with respect to the impact on visual function, survival, treatment techniques, and consequences of treatment. Based on these experiences, future strategies in the management of childhood low grade glioma are discussed. Results: Although the efficacy of radiation therapy has been well known for more than 60 years, there are still many open questions. Location and extent of disease often precludes aggressive surgery and a conservative approach is used today with the aim of preserving visual function. Evaluation of published reports is difficult because of short follow-up periods and the failure to present findings and results in a comparable way. Even with the shortcomings of the reports available in the literature primarily concerning indications, dose-response effects, timing, and use of ‘optimal’ treatment fields, fractionated radiation therapy plays an important role in the management of low grade gliomas. Improved or stable visual function is obtained in approximately 90% of the cases. With doses of 45-54 Gy with standard fractionation and limited treatment fields, high local tumor control in up to 80% and more can be achieved. Past series comprising children younger than 5 years of age, however, have reported high rates of severe late effects when using large treatment fields and inadequate fractionation schemes. There is consent today to employ radiotherapy in progressive disease only and that newer technologies, such as 3D treatment planning (conformal radiotherapy), should be used. Recent experiences have achieved promising initial outcome, while reducing treatment-induced toxicity. Stereotactic techniques using high single doses are of minor importance. Conclusions: Radiation therapy is an effective treatment modality with regard to tumor control and improvement and/or preservation of vision. Presently, it is recommended that radiotherapy be initiated in progressive disease in older children and that chemotherapy be given to younger children. More prospective studies are needed (such as the forthcoming study of the International Society for Paediatric Oncology (SIOP-LGG RT 2000) to address the impact of modern radiation therapy technologies on the outcome, including consequences, of treatment.