Abstract
INTRODUCTION
Clinical target volume (CTV) for radiotherapy of glioblastoma is typically defined as an isotropic 2 cm expansion to the area of residual enhancement on T1 weighted MR imaging plus the surgical bed. Tumor growth models allow for incorporating the biological information about preferential spread along the white matter fibers in target definition. We assessed the value of growth driven CTV in the prediction of non-central recurrences.
MATERIALS AND METHODS
Five glioblastoma patients treated with radiotherapy (dose 60 Gy in 30 fractions) with recurrences extending outside the 95% isodose were selected out of 56 patients. The brain was segmented into white matter, grey matter and cerebrospinal fluid. Anatomic boundaries were delineated manually. A reaction-diffusion growth model was used assuming uniform proliferation throughout the brain and difference in white and grey matter diffusion of a factor 10 with no migration across the barriers. The volume of growth driven CTV (gCTV) corresponded the standard CTV. The volumetric comparison was performed using the shortest distance (SD) between all surface points in the recurrence volume and respective CTV and gCTV.
RESULTS
Three of five recurrences were distant, seperated at minimum 3 cm from the resection cavity or the residual enhancement. The median CTV and recurrence volume was 236 cm3 (range: 175-240 cm3) and 89 cm3 (range: 0.9-112 cm3), respectively. The median SD in the recurrence volume decreased from 7.0 mm (range: 4.7-36.0 mm) for CTV to 5.5 mm (range: 2.9-28.1 mm) for gCTV indicating that gCTV was closer to the recurrence volume. Two out of three distant recurrences were not encompassed by the gCTV while no distant recurrences were within the CTV.
CONCLUSION
The growth driven CTV appears promising in the prediction of marginal recurrences outside 95% isodose compared to standard CTV.