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Neurovisual outcome following proton radiation therapy
I L Habrand1, M Austin-Seymour, S Birnbaum
1Department of Radiation Medicine, Massachusetts General Hospital, Harvard Medical School, Boston 92114.
Summary
Proton irradiation for upper clivus tumors can cause visual complications. Doses around 55 CGE to optic nerves and chiasm may lead to a 10% complication rate, suggesting a need for careful dose management.
Area of Science:
- Radiation oncology
- Neuro-oncology
- Ophthalmology
Background:
- Upper clivus tumors often require radiation therapy, posing a risk to nearby optic pathways.
- Proton irradiation is a treatment modality used for these tumors, with specific dose considerations.
- Understanding the tolerance of optic nerves (ON) and optic chiasm to radiation is crucial for minimizing visual morbidity.
Observation:
- Twenty patients with upper clivus tumors received proton irradiation.
- Fifteen patients with known neurovisual status had dose-volume histograms (DVH) analyzed for optic nerves and chiasm.
- Two patients experienced progressive visual deterioration attributed to radiation-induced optic nerve or chiasm injury.
Findings:
- A complication rate of 20% was observed when a substantial portion of the optic nerve received 65 Cobalt Gray Equivalent (CGE).
- Complication rates were lower at 55 CGE: 12.5% for optic nerves and 7.5% for the optic chiasm.
- The study suggests a tolerance dose for a 10% major complication rate is approximately 55 CGE for optic pathways.
Implications:
- When treating upper clivus tumors with high radiation doses, careful exclusion of optic nerves and chiasm up to 55-60 Gy is recommended.
- This finding aids in optimizing radiation planning to balance tumor control and preservation of visual function.
- Further research may refine tolerance doses and explore predictive factors for radiation-induced visual complications.