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.