2 I METHODS
This study was a retrospective review of a cohort of children, younger
than 21 years of age at the time of receiving cranial proton radiation,
for tumors of the central nervous system (CNS). All patients received
oncology care at the Jimmy Everest Center for Cancer and Blood Disorders
(University of Oklahoma Health Sciences Center), proton radiation at
ProCure Proton Therapy Center, and ophthalmology follow-up for all but 1
patient, at the Dean McGee Eye Institute (DMEI) in Oklahoma City. Data
was extracted from patient charts regarding demographic and clinical
details, including diagnosis and treatment. Patients with ophthalmology
data available were included in the final analysis. For each patient,
complete details of the first and last formal eye exam, were recorded.
Their ophthalmology charts were reviewed for details regarding the
detection and management of 4 complications: cataract, dry eyes, retinal
changes (pigmentation, scarring, mottling, hemorrhage, vaso-occlusion)
and glaucoma. The severity of dry eyes was graded as mild if no
treatment was needed, moderate if artificial tears were prescribed, and
severe if serum tears, cyclosporine ophthalmic suspension or punctal
plugs were required. For patients found to have an ocular complication,
previous visit notes were reviewed to determine the time when it was
first detected. Finally, visual acuity for each eye, at the first and
last eye exams, were recorded and compared. Radiation treatment details
documented were the planning treatment volume, radiation dose in Gy
(Gray) RBE (relative biological effectiveness) in total, as well as to
the lens, cornea, and lacrimal glands on each side. Patients who did not
have ophthalmology data available, were excluded from the study.
Descriptive statistics were computed for all demographic and clinical
variables. Patients included in the study were compared with those
excluded due to lack of ophthalmology data, for differences in
distribution by gender, age at radiation, tumor location and radiation
volume. Multivariable analysis was performed to identify significant
risk factors for the development of ocular complications after cranial
proton radiation. Categorical variables such as gender, tumor location,
and radiation volume were compared between groups using the Chi-square
test or Fisher’s Exact test, as appropriate. Continuous variables such
as age at radiation start, mean dose to lens, retina, and cornea were
assessed for normality using the Shapiro-Wilk test, and group
comparisons were made using Student’s t-test, or Wilcoxon-Mann-Whitney
test, as appropriate.