Novel target volume delineation method in glioblastoma
MO-0555
Abstract
Novel target volume delineation method in glioblastoma
Authors: Ilinca Popp1, Marina Bulach1, Angelika Bilger1, Eleni Gkika1, Anca-L. Grosu1,2
1Medical Center - University of Freiburg, Department of Radiation Oncology, Freiburg, Germany; 2German Cancer Consortium (DKTK), Partner Site Freiburg, Freiburg, Germany
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Purpose or Objective
For target volume delineation in glioblastoma there are currently two major consensus guidelines being used, the one of the European Organization for Research and Treatment of Cancer (EORTC) and the one of the Radiation Therapy Oncology Group (RTOG). The resulting planning target volume (PTV) is often large and includes considerable volumes of healthy brain tissue. The primary aim of this study was the analysis of a novel PTV delineation method based on fluid-attenuated inversion recovery (FLAIR)-alterations in magnetic resonance imaging (MRI).
Material and Methods
A total of 89 patients were retrospectively included in this study. Postoperative MRI-scans at the time of radiation treatment planning were used to define the target volume according to EORTC, RTOG and the FLAIR method. For the latter, the gross tumor volume (GTV) was defined as the FLAIR-altered area, including the resection cavity and any contrast enhancing lesions. The clinical target volume (CTV) was defined as GTV + 2 mm and the PTV was defined as CTV + 3 mm. Patients were treated based on the EORTC volume with a total dose of 60 Gy in 30 fractions. Recurrences were delineated on follow-up MRI-scans at their first occurrence. We performed a volumetric comparison of the defined PTVs and analyzed the recurrence pattern in relation to all three target volumes.
Results
The FLAIR target volume with a median of 179 ml was significantly smaller than the target volumes according to the EORTC and RTOG methods (292.9 ml and 452.9 ml, p<0.001). The recurrence pattern of the FLAIR target volume was significantly similar to that of the EORTC method (Kappa=0.7, p<0,001). The percentage of in-field recurrences was 79.5% vs. 80.8%, marginal recurrences occurred in 11% vs. 8.9% of patients, while out-of-field recurrences were noted in 9.6% vs. 10.3% of cases. With the RTOG method, there were fewer marginal (4.1%) and out-of-field (5.5%) recurrences compared to EORTC and FLAIR.
Conclusion
Even when considering the reduced volume of the FLAIR-PTV, the majority of recurrences occurred in field. The new target volume definition method yields comparable results with the commonly used EORTC method, while including significantly less surrounding tissue and can therefore be considered as valid option. A prospective investigation of this method for possible future consolidation of target volume reduction is planned.