Volumetric response evaluation after intensity modulated radiotherapy in patients with supratentorial gliomas

Radiotherapy is frequently indicated to treat cerebral gliomas. Accurate response evaluation after radiotherapy is essential to determine the efficacy of treatment. We retrospectively analyzed the volumetric tumor response after simultaneous integrated boost-intensity modulated radiotherapy (SIB-IMRT) in patients with gliomas. Thirty-five patients (Grade II, 7 patients; Grade III, 12; and Grade IV, 16) were treated with SIB- IMRT with a median total dose of 55.9 Gy/26 fractions for Grade II and 60 Gy/25 fractions for Grade III-IV tumors. Tumor responses were evaluated for enhancing volume on post- gadolinium T1-weighted images (V_gd) and hyper-intensity volume on T2-weighted FLAIR images (V_fl) on serial MRIs. With the median follow-up of 24.0 months, overall response rates (RRs) were 57% for V_gd and 51% for V_fl. Tumor grade was predictive of response favoring the lower grade in V_fl with RRs of 86% for Grade II, 75% for Grade III, and 19% for Grade IV tumors (p 5 0.004). Time to 50% or greater volume reduction (T50) in V_gd was 8 months for grade III. The T50 in V_fl was approximately 24 months both for Grade II and III tumors. Majority of Grade IV tumors continued to progress and never reached the T50 in V_gd or V_fl. Responders survived longer than non-responders for V_gd and V_fl. Volume response after radiotherapy was dependent upon tumor grade and time. LGGs are very responsive to radiotherapy with the RRs of 86% in V_fl. The response of V_fl is more protracted compared to V_gd. Further investigation is needed to determine the clinical significance of volumetric response evaluation.