Tejinder Kataria, Kuldeep Sharma, Pranav Chadha, Dhanraj Jangid and Kulbir Ahlawat
Background: Glioblastoma is the commonest brain tumor of adults carrying a very poor prognosis. Targeting the tumor accurately during surgery and radiotherapy holds promise in future. PET with various tracers is being explored worldwide to enhance the accuracy of target delineation. This study was undertaken to evaluate the differences and correlation between the target volumes delineated by using MRI and 18F-FDG PET during RT planning and to evaluate whether inclusion of PET is helpful in better coverage of high risk area for recurrence.
Materials and Methods: Fifteen post-operative patients of glioblastoma were prospectively enrolled. Planning images were acquired with CT, MRI and delayed PET. Image fusion was done to delineate MR-based (GTV-MR, CTV-MR, PTV-MR), PET-based (GTV-PET, CTV-PET) and combined (GTV-X, CTV-X) volumes. Only MR-based volume was used for actual treatment. Mean volumes were calculated for each group for volumetric analysis.
Concordance Index (CI) was calculated for GTV and CTV as CI = [(M + P)/X] -1, to find correlation between volumes, such that full concordance and full non-concordance between MRI and PET volumes would yield a value of 1 and 0 respectively.
On recurrence, the recurrent volumes (rVol) were marked and correlated with initial CTV-MR, CTV-PET and CTV-X to calculate the proportion of rVol covered within these volumes.
Observation and Results: Mean GTV-MR, GTV-PET and GTV-X were 84.4 cc, 11 cc and 89.2 cc, respectively. Median follow-up was 16.6 months for the overall group and 26.1 months for the surviving patients. Overall 1,2 years survival was 80% and 20% respectively.
Conclusion: Inclusion of PET-based abnormality while delineating the target volumes for glioblastoma leads to a non-significant increase in target volumes with better coverage of the high-risk region. Thus, targeting the common volume (CTV-X) for treatment may prove beneficial in avoiding marginal recurrences in glioblastoma.
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