16 September 2014
Posted in Pearls in Ophthalmology
By Brooke Strickland
In this study, researchers wanted to measure the safety and effectiveness of low-voltage, external-beam, stereotactic radiotherapy (SRT) for patients diagnosed with neovascular age-related macular degeneration (AMD). The study included 230 randomized patients from various centers. They had all been diagnosed with neovascular AMD and had received ≥3 ranibizumab or bevacizumab injections within the previous year. They all required treatment at enrollment. Participants received 16 Gray, 24 Gray, or sham SRT. All arms received pro re nata (PRN) ranibizumab for 12 months, with PRN bevacizumab or ranibizumab thereafter. Researchers noted the average number of PRN injections, best-corrected visual acuity (BCVA), loss of <15 Early Treatment of Diabetic Retinopathy Study letters, change in optical coherence tomography central subfield thickness, and variation in angiographic total lesion area and choroidal neovascularization (CNV) area.
Results showed that at the two year mark, the 16 and 24 Gray arms received fewer PRN treatments compared with sham. Change in average BCVA was −10.0, −7.5, and −6.7 letters for the 16 Gray, 24 Gray, and sham arms, with 46 (68%), 51 (75%), and 58 participants (79%) losing <15 letters. Mean central subfield thickness decreased by 67.0 μm, 55.4 μm, and 33.3 μm. Average total active lesion area increased by 1.0, 4.2, and 2.7 mm2, respectively. Average CNV area reduced by 0.1 mm2 in all groups. An independent reading center noticed microvascular abnormalities in 6 control eyes and 29 SRT eyes, of which 18 were credited to radiation; however, only 2 of these possibly affected vision. An exploratory subgroup analysis found that lesions with a greatest linear dimension ≤4 mm (the size of the treatment zone) and a macular volume greater than the median (7.4 mm³) were more responsive to SRT, with 3.9 PRN injections versus 7.1 in comparable sham-treated participants. (1)
What to take away from the study: A single dose of SRT can considerably reduce intravitreal injections over a two year time span. Radiation can help with microvascular change, but approximately only 1% of patients will see a change in vision. The best response is when AMD lesions are leaking and fit within the treatment zone.
1. 1. Jackson, Timothy, L., PhD, FRCOphth, Chakravarthy, Usha, MD, PhD, Slakter, Jason, S., MD, Muldrew, Alyson, PhD, Shusterman, E. Mark, MD, O’Shaughnessy, Denis, PhD, Arnoldussen, Mark, PhD, Gertner, Michael, E., MD, Danielson, Linda, MSc, Moshfeghi, Darius, M., MD on the behalf of INTREPID Study Group. “Sterotactic Radiotherapy for Neovascular Age-Related Macular Degeneration.” Ophthalmology. Published online September 7, 2014. Accessed online September 12, 2014. http://www.aaojournal.org/article/S0161-6420%2814%2900687-3/abstract
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