Contrast enhancing residual tumor in post-operative Glioblastoma multiforme (GBM) as a predictor of overall survival (OS) and progression free survival (PFS) was evaluated.

We retrospectively collected data of treated GBM patients using fused post-operative CEMRI brain with radiotherapy planning CECT and analysed the residual tumor volume.

We included 48 patients of GBM treated between March 2017 to March 2024. Post tumor resection, 34 (70.9%) patients received radiotherapy (RT) to dose 59.4-60 Gray in 30 fractions, 14 (29.2%) received 40 Gray in 15 fractions. All patients received concurrent temozolomide 75 mg/m² followed by adjuvant temozolomide 100-200 mg/m² for six cycles. Using fused CEMRI T1weighted and T2 FLAIR images residual tumor volume was determined. Univariate analysis of various prognostic factors for OS and PFS were determined using Log rank test, Kaplan Meier survival curve and Cox proportional hazard models.

Mean age 43 years, pre-radiotherapy KPS <80 in 24 (50%) and >80 in remaining. Post-surgery tumor size was <4cm in 36 (75%) and >4cm in 12 (25%) patients. Mean GTV CEMRI-T1 volume 87.96 cm³, mean CTV 318.12 cm³, mean PTV 407.50 cm³, mean tumor brain volume ratio [(PTV volume /total brain volume) X 100] was 31.46 %, mean extent of resection= [PTV-GTVT1c/PTV] X 100 was 79.45%. Overall mean OS and PFS were 16.2 and 13.8 months. Median OS was significantly more in tumor brain volume ratio <29 % (31.7vs14.2 months) p=0.048, pre and post RT KPS <80, RT dose 59.4-60 Gray (p=0.012), PTV volume<400cc (p=0.029). Median PFS was significantly more in tumor size <4 cm (26.3vs14.9 months), pre- RT-KPS <80 (p=0.37), RT dose 59.4-60 Gray (p=0.026).

Pre and post RT KPS <80, tumor brain volume ratio <29 % and PTV volume <400cc was associated with better OS. PFS was more in tumor size <4 cm, pre- RT-KPS <80, RT dose 59.4-60 Gray.