Introduction: The role of stereotactic radiosurgery (SRS) for glioblastoma recurrence in patients who received radiotherapy at diagnosis remains unclear, specifically the role of concurrent chemotherapy and radionecrosis risk. Larger studies would help inform proper SRS indications, efficacy and risks in recurrent disease.
Methods: We retrospectively reviewed our radiosurgery database from 1991-2013 to identify patients who underwent Gamma Knife SRS for recurrent glioblastoma. We collected clinical parameters and used Cox proportional hazards modeling to identify factors associated with increased time to progression.
Results: 178 GBM patients received Gamma Knife a median of 8.7 months (range 2.1-195.8 months) after diagnosis. Patients undergoing radiosurgery had mean age of 53 (range 5-85) and were 58% male. 75% of patients had one treatment target (range=1-6). Median total targeted volume was 6.7 cm3 (range 0.3-39.0) with a mean of 16.7 Gy (range 12-20) prescribed to the 50% isodose line. Median progression-free and overall survival were 4.3 (range=0.5-83.4) and 9.4 months (range=1.4-84.6) from the time of SRS, respectively. Concurrent chemotherapy was given with radiosurgery in 75% of patients, with common agents including temozolomide (30%), CCNU (24%) and BCNU (13%). Multivariate modeling including target volume, 50% isodose prescription, concurrent chemotherapy, age, and gender revealed only younger age (p=0.04) and increased isodose prescription (p=0.006) to be associated with increased time to progression. 46 patients went on to have craniotomy a mean of 11.5 months after SRS with 61% showing radionecrosis or mixed tumor and radionecrosis versus 37% showing recurrent tumor. The necrosis/mixed group had a lower mean isodose prescription compared to the tumor group (16.4 versus 17.6 Gy, p = 0.0025).
Conclusions: Gamma Knife SRS may benefit a subset of focally recurrent glioblastoma patients, particularly those who are younger. Higher SRS prescriptions are associated with longer progression-free survival but do not seem to have higher risk of symptomatic treatment effect in our cohort.
Patient Care: This project will inform clinicians about when it may be clinically appropriate to utilize Gamma Knife radiosurgery for the treatment of recurrent glioblastoma. GBM has limited evidence-based effective treatment options, therefore it will be beneficial for physicians who treat GBM to learn more about our institutional experience with the technology. Furthermore, this research will elucidate which patients are more likely to benefit from the therapy. Finally, we review our progression and survival statistics which can help clinicians provide more accurate prognostic information to prospective patients considering Gamma Knife as part of their GBM treatment regimen.
Learning Objectives: By the conclusion of this session, participants should be able to: 1) Describe the current literature surrounding the usage of stereotactic radiosurgery for the treatment of recurrent GBM 2) Understand the indications, efficacy and potential toxicities of using Gamma Knife SRS for recurrent disease 3) Identify factors which suggest whether a recurrent GBM patient has higher risk of progression post Gamma Knife therapy