Stereotactic Radiosurgery for Small (<1cc) Recurrent Nodular Idh-wild Type Glioblastoma: A Single Institution Experience

Introduction: Glioblastoma (GBM) is the most common and lethal primary malignant brain tumor in adults. Small recurrent nodular GBM is routinely treated by a single-fraction Stereotactic Radiosurgery (SRS) treatment to the contrast-enhancing target on a T1 MRI scan, although its effectiveness has not been previously investigated.

Methods: We retrospectively reviewed clinical and radiological outcomes of patients with small (volume smaller than 1cc) recurrent nodular IDH-wt GBM who underwent CyberKnife SRS at our institute between January 2013 and September 2022.

Results: A total of five patients (median age 53 years) with a total of nine lesions (range: 1–3 per patient) underwent SRS. All patients received standard chemoradiation per Stupp’s protocol. Additional chemotherapy regimens included bevacizumab, lomustine, carmustine, and irinotecan, and supplementary radiation included CyberKnife SRS to the resection cavity with 2mm margins. MGMT promotor hypermethylation was found in 3 out of 5 patients. The median target volume was 0.66 cc (range: 0.16-1.0). SRS was delivered as a single fraction for all targets, with a median margin dose of 20 Gy (range 18-24) to a median isodose line of 71% (range 70-80). The 3-, 6-, and 12-month local tumor control (LTC) rates for lesions were 77.8%, 66.7%, and 33.3%, respectively. Median progression-free survival (PFS) was 7 months (range 2–14 months), and median overall survival (OS) was 35 months (range 17–52 months). None of the patients presented adverse radiation effects. Interestingly, the only lesion that did not present radiological progression, did not present a connection with the MRI-FLAIR hyperintense area surrounding the original tumor.

Conclusion : By targeting the T1MRI contrast enhancing target in a single fraction, SRS leads to a relatively good local tumor control of small recurrent nodular GBM, with no adverse effect. Further research is necessary to improve SRS outcome by developing new contouring and dosing strategies.