RT-03 POSTOPERATIVE CYBERKNIFE HYPOFRACTIONATED RADIOTHERAPY FOR THE ELDERLY PATIENTS WITH GLIOBLASTOMA

INTRODUCTION: In recent years, hypofractionated radiotherapy (HRT) 40Gy in 15 fractions with concomitant temozolomide(TMZ) has come to be used as standard treatment for elderly glioblastoma. However, the treatment duration of 3–4 weeks for radiation is not enough short, and there is also a problem of radiation sickness. We performed hypofractionated stereotactic radiotherapy with CyberKnife (CK) for less than 2weeks. We retrospectively analyzed eight newly diagnosed elderly patients with glioblastoma treated by CK. METHODS: Surgical cavity, contrast enhanced lesion, FLAIR high signal intensity area were set as gross tumor volume (GTV). To planned target volume (PTV) as GTV + 2 mm, Marginal dose (D95) 35 Gy in 5 fractions (Fr) was prescribed. The dose prescription and number of fractions were adjusted taking into consideration dose distribution, dose-limiting for important organs such as optic chiasm and brainstem. RESULTS: The eight patients consisted of 3 men and 5 women. The median age was 78 (range 68–84) years old. All patients were pathologically diagnosed as glioblastoma. Two of 8 cases had undergone gross total removal of contrast area. Median postoperative KPS was 70 (40–80). Thirty three (28–33.5) Gy was administered in 5 (3–10) Fr to PTV 117 (44–243) ml. TMZ was used in 7 patients. Bevacizumab (BEV) was used together from 4 weeks after surgery in 5 patients. Progression-free survival was 6.5 (2.9–10.6) months and overall survival was 17.5 (7.1–28.5) months. 7 patients had experienced controllable hypertension with antihypertensive agents, Two patients had suffered from deep vein thrombosis, and anticoagulation therapy was used. One patient had nausea and malaise due to TMZ and had continue BEV alone. Asymptomatic cerebral infarction in the radiation field was observed in a patient. CONCLUSION: CK treated in less than half duration of conventional HRT is expected as less invasive treatment.