Radiation optic neuropathy after megavoltage external-beam irradiation: analysis of time-dose factors.
OBJECTIVE
To investigate the risk of radiation-induced optic neuropathy according to total radiotherapy dose and fraction size, based on both retrospective and prospectively collected data.


METHODS
Between October 1964 and May 1989, 215 optic nerves in 131 patients received fractionated external-beam irradiation during the treatment of primary extracranial head and neck tumors. All patients had a minimum of 3 years of ophthalmologic follow-up (range, 3 to 21 years). The clinical end point was visual acuity of 20/100 or worse as a result of optic nerve injury.


RESULTS
Anterior ischemic optic neuropathy developed in five nerves (at mean and median times of 32 and 30 months, respectively, and a range of 2-4 years). Retrobulbar optic neuropathy developed in 12 nerves (at mean and median times of 47 and 28 months, respectively, and a range of 1-14 years). No injuries were observed in 106 optic nerves that received a total dose of < 59 Gy. Among nerves that received doses of > or = 60 Gy, the dose per fraction was more important than the total dose in producing optic neuropathy. The 15-year actuarial risk of optic neuropathy after doses of > or = 60 Gy was 11% when treatment was administered in fraction sizes of < 1.9 Gy, compared with 47% when given in fraction sizes of > or = 1.9 Gy. The data also suggest an increased risk of optic nerve injury with increasing age.


CONCLUSIONS
As there is no effective treatment of radiation-induced optic neuropathy, efforts should be directed at its prevention by minimizing the total dose, paying attention to the dose per fraction to the nerve, and using reduced-field techniques where appropriate to limit the volume of tissues that receive high-dose irradiation.
Department of Radiation Oncology, University of Florida College of Medicine, Gainesville.
J T
JT
Parsons
F J
FJ
Bova
C R
CR
Fitzgerald
W M
WM
Mendenhall
R R
RR
Million
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D002675:Child, Preschool; D004307:Dose-Response Relationship, Radiation; D005123:Eye / Q000528:radiation effects; D005260:Female; D006258:Head and Neck Neoplasms / Q000532:radiotherapy; D006801:Humans; D007223:Infant; D008297:Male; D008875:Middle Aged; D009900:Optic Nerve / Q000528:radiation effects*; D009901:Optic Nerve Diseases / Q000209:etiology*; D011446:Prospective Studies; D011832:Radiation Injuries / Q000209:etiology*; D011835:Radiation Protection; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D011882:Radiotherapy, High-Energy / Q000009:adverse effects*; D012189:Retrospective Studies; D013997:Time Factors; D014786:Vision Disorders / Q000209:etiology