External beam radiotherapy for head and neck cancers is associated with increased variability in retinal vascular oxygenation.
BACKGROUND
Radiation retinopathy is a possible post-treatment complication of radiation therapy. The pathophysiologic mechanism is hypothesized to be microvascular in origin, but evidence is limited. In an effort to study retinal oxygenation in these patients, we herein evaluate the repeatability and variability of retinal oximetry measurements in subjects who had previously received radiation and make comparisons to a cohort of unirradiated subjects.


METHODS
Using retinal oximetry, a non-invasive imaging modality, we performed in vivo measurements of arteriole (SaO2) and venule SO2 (SvO2) in subjects (n = 9, 18 retinas) who had received incidental radiation to their retinas (≥ 45 Gy to one retina) and in healthy subjects (n = 20, 40 retinas). A total of 1367 SO2 observations on 593 vessels in 29 persons were analyzed to assess three sources of variance in vessel SO2: 1) variance in repeated measurements of the same vessel ("repeatability"), 2) variance in different vessels within the same subject ("within-subject variability"), and 3) variance between subjects ("between-subject variability").


RESULTS
Retinal oximetry measurements were highly repeatable in both irradiated patients and unirradiated subjects. The within-subject variability of SvO2 and SaO2 measurements constituted the highest component of variance in both groups and was significantly higher in venules vs. arterioles (relative effect size 1.8, p<0.001) and in irradiated subjects vs. unirradiated subjects (relative effect size 1.6, p<0.001).


CONCLUSIONS
Retinal oximetry is a highly repeatable technology and can be reliably used to study vascular oxygenation in irradiated subjects. Different vessels within the same subject exhibit a high degree of variability, suggesting that pooled analyses of multiple vessels are most likely to be informative of regional retinal oxygenation. Finally, irradiated subjects exhibited significantly higher within-subject variability in SO2 measurements, suggesting that radiation may cause regional alterations in retinal oxygen delivery and/or metabolism.
Department of Radiation Oncology, Memorial Sloan-Kettering Cancer Center, New York, New York, United States of America.
Daniel S
DS
Higginson
Alok
A
Sahgal
Michael V
MV
Lawrence
Sarah
S
Moyer
Mihaela
M
Stefanescu
Adam K
AK
Willson
Bahjat
B
Qaqish
Adam
A
Zanation
Lawrence B
LB
Marks
Seema
S
Garg
Bhishamjit S
BS
Chera
D000328:Adult; D000368:Aged; D000704:Analysis of Variance; D001160:Arterioles / Q000378:metabolism / Q000528:radiation effects; D015331:Cohort Studies; D005260:Female; D006258:Head and Neck Neoplasms / Q000532:radiotherapy*; D006801:Humans; D008297:Male; D055806:Microvessels / Q000378:metabolism* / Q000528:radiation effects*; D008875:Middle Aged; D010092:Oximetry; D010100:Oxygen / Q000378:metabolism*; D011878:Radiotherapy / Q000009:adverse effects*; D015203:Reproducibility of Results; D012160:Retina / Q000503:physiopathology / Q000528:radiation effects*; D014699:Venules / Q000378:metabolism / Q000528:radiation effects
D010100:Oxygen