Abstract
Despite increasing use of reirradiation (reRT) in recurrent glioma, there are no standardized criteria to evaluate response to therapy. We aimed to identify imaging and dosimetry features to help define criteria for treatment failure. 25 glioma patients reirradiated at NCI NIH between 2010 and 2016 with available diffusion weighted MRI (DWI) were included. reRT plans were coregistered with DWI at 1 and 2 to 3 months. Enhancing and nonenhancing abnormalities were contoured and analysed in conjunction with dose distribution using ECLIPSETM. Mean recurrence GTV and PTV were 24.8cc and 111.5cc respectively. Median initial dose and reRT dose were 60Gy and 30Gy respectively, median cumulative dose was 96Gy. Median follow-up was 5 months with median overall survival (OS) of 5 months (1.9-95). At 1month, enhancement was increased in 11 (44%) (4 outside the 50% isodose, 7 within the 100% isodose), stable or decreased 13(52%). 13 (52%) maintained increased perfusion. All patients with enhancement outside of the 50% isodose line displayed increased perfusion and all had immediate radiographic and clinical progression and a median OS of 1 month. Increased FLAIR volume at 1 month irrespective of relationship to isodose line did not predict for progression. At 2-3 months, 1 had complete response, 7 (28%) stable/improved enhancement, 6 (24%) progressed clinically, 7 (28%) had increased enhancement and/or FLAIR volume. No statistically significant correlation was identified between pre or post reRT steroid use/dose increase, bevacizumab use, enhancing and T2 FLAIR volume, restricted diffusion and clinical progression or OS. Documenting progression following reRT remains challenging. In our series, perfused enhancement outside of the reRT field was associated with rapid progression, while increased enhancement or T2 FLAIR volume did not necessarily result in progression. Progression post reRT will need to be based on close examination of DWI and reRT isodose lines in conjunction with clinical decline.
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