Patterns of Failure Following Stereotactic Radiosurgery (SRS) for Recurrent Glioblastoma Multiforme (GBM)

Purpose/Objective(s):Despite surgical resection, temozolomide, and radiation therapy, most patients with GBM recur. Effective strategies against recurrence have yet to be elucidated, and may involve systemic treatment, surgery, and/or re-irradiation. Re-irradiation with SRS targets smaller volumes and may have decreased side effects compared to fractionated involved field radiation therapy. However, it is unclear how it affects the overall disease progression. Here, we present our experience of re-irradiation for GBM to report the patterns of failure and overall survival following SRS.Materials/Methods:We reviewed 36 consecutive patients treated with Gamma Knife SRS for recurrent GBM between June 2006 and July 2013. The median age was 59 years (range, 31-79) and median interval from initial radiation therapy course was 11 months (range, 1-56). The target was enhancing tumor with median volume of 4.6 cc (range, 0.6-24.9) and median prescription dose of 18 Gy to the 50% isodose surface (range, 12-22). Six (17%) patients were treated to 2 or more recurrent volumes. In addition, 28 (78%) received bevacizumab and 2 (6%) received temozolomide. MRIs at time of enhancing tumor progression were fused with treatment planning MRIs for analysis. Recurrences were classified as infield, marginal or distant based on percent volume receiving the prescription dose and maximum dose in the recurrence volume. Statistical analysis was performed with the Mann Whitney U test.Results:With a median follow up of 11 months, 13 (36%) patients were alive at last follow up, 1 (2%) was lost to follow up, and 22 (61%) were deceased. Median overall survival was 8 months. Twenty-five (69%) patients had treatment failure after SRS, with a median time to progression of 6 months (range, 1-31). At time of recurrence, 64% had a detriment in KPS. There were 12 (48%) in field failures, 8 (32%) marginal, and 5 (16%) distant. Median time to progression was 4 months for in field failures, 6 months for marginal and 6 months for distant. There was no significant difference in time to progression in patients with infield failure vs distant failure (p=0.18). Eighteen failures (75%) were also associated with FLAIR progression. The median maximal dose received by recurrent tumors was 25 Gy (range, 0.4 - 37.7) with 76% of recurrences in areas receiving more than 20 Gy.Conclusions:Our study of patterns of failure following SRS for recurrent GBM found that the majority of failures were infield, followed by marginal, with distant failures the least likely. In field failures also had the shortest median time to disease progression. Further investigation comparing these data with patterns of failure after fractionated re-irradiation may inform the best strategy for re-irradiation.

MSRO42-06

Patterns of Failure Following Stereotactic Radiosurgery (SRS) for Recurrent Glioblastoma Multiforme (GBM)