Survival following CyberKnife Radiosurgery and Hypofractionated Radiotherapy for Newly Diagnosed Glioblastoma Multiforme

Abstract

Current therapeutic goals for treatment of Glioblastoma Multiforme (GBM) involve gross total resection followed by multifractionated focal external beam radiation therapy (EBRT). Patients treated with optimal therapy have a median survival of approximately 12–15 months. In the present study, we sought to determine whether a hypofractionated dosing schedule using CyberKnife is at least as effective as multifractionated focal EBRT. A retrospective analysis was conducted on 20 histopathologically confirmed GBM patients treated with CyberKnife at Okayama Kyokuto Hospital in Japan after gross total resection (n=11), subtotal resection (n=8), or biopsy (n=1). Eight patients also received adjuvant ACNU and Vincrisitine chemotherapy according to local protocol; however, no patient received any other form of radiation besides post surgical/biopsy CyberKnife treatment. The treated tumor volumes ranged from 9.62 cm3− 185.81 cm3 (mean: 86.08 cm3). The marginal dose (D90) ranged from 19.99 Gy-41.47 Gy (mean: 34.58 Gy) with a maximum mean dose of 43.99 Gy (range: 23.33 Gy-56.89 Gy). The prescribed isodose line ranged from 50.38%–85.68% with a mean of 79.25%. Treatment was delivered in 1–8 fractions (mean: 5.65). Patients were followed from 2–36 months (mean: 16.45 months). Overall median survival was 16 months with 55% of patients alive at 12 months and 34% of patients alive at 24 months. Median survival of patients in Recursive Partitioning Analysis (RPA) classes III or IV was 32 months versus 12 months for those in RPA class V. Median survival for patients who received gross total resection was 36 months versus 8 months for those who underwent subtotal resection or biopsy. The results of this study using CyberKnife stereotactic radiosurgery (SRS) and hypofractionated radiotherapy compared favorably to historic data using focal EBRT in newly diagnosed post surgical GBM patients. A larger prospective analysis that compares CyberKnife SRS and hypofractionated radiotherapy to focal EBRT is warranted.