OCT 24, 2013
This double-masked, sham-controlled study found that a single dose of stereotactic radiotherapy (SRT) reduced the frequency of anti-VEGF retreatment over a 12-month period compared with anti-VEGF monotherapy in patients with previously treated wet AMD.
Researchers used the IRay Radiotherapy System (Oraya Therapeutics), a low-voltage, external-beam SRT instrument developed to deliver ionizing radiation noninvasively to wet AMD lesions.
Subjects were 230 patients with wet AMD onset within the previous three years who had received three or more injections of ranibizumab or bevacizumab in the preceding year and who needed continuing ranibizumab or bevacizumab treatment. They were randomized to one of four arms: 16 Gy stereotactic radiotherapy plus PRN ranibizumab, sham 16 Gy stereotactic radiotheraphy plus PRN ranibizumab, 24 Gy stereotactic radiotherapy plus PRN ranibizumab, or sham 24 Gy stereotactic radiotherapy plus PRN ranibizumab.
The stereotactic radiotherapy arms required significantly fewer ranibizumab injections compared with the sham arms, achieving the study’s primary outcome. The total number of ranibizumab injections was very low in all arms, with 2.64 injections in the 16 Gy arm, 2.43 in the 24 Gy arm, and 3.74 in the sham arms. There were no differences in visual acuity or lesion size, nor were there any cases of radiation retinopathy.
The most important criticism of the study design is a lax retreatment criteria for ranibizumab, which the researchers acknowledge. They required a 100 micron increase in central subfield thickness from the lowest previous OCT measurement, new or increased hemorrhage, or a drop of at least five letters. Most would agree that these criteria promote undertreatment of wet AMD. However, the authors note that the retreatment criteria were applied equally across all arms.