Materials and Methods: 30 lesions from 23 malignant astrocytomas (2 AAs and 21 GBMs) were enrolled. Before irradiation, Met-PET was performed in all cases. In each ROI, maximum uptake of Met was determined relative to a corresponding contralateral region (Tmax/Nave). Among the 23 patients, 10 were treated by 3D-CRT with conventional fractionation (40Gy/20Fxs for FLAIR-high area with boost of 20Gy/10Fxs for enhanced lesion), while the remaining 13 were treated by hypofractionated high-dose IMRT.

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... In the IMRT, 3-layered PTVs were contoured (PTV-1: enhanced lesion with 5mm margin, PTV-2: 15mm surrounding the PTV-1,PTV-3: FLAIR-high area) and different doses (68Gy for PTV-1, 40Gy for PTV-2 and 32Gy for PTV-3) were delivered by 8 fractions. Concurrent and adjuvant temozolomide was administrated in all cases. After treatment, MRI was performed with an interval of 1 or 2 months. If the recurrent tumor was observed, Met-uptake at the recurrent point and delivered dose at the same point in the treatment plan of irradiation were retrospectively calculated. The delivered dose was standardized using biologically effective dose (BED, alpha/beta=10). The ratio of Met-uptake/BED was compared with tumor control using logistic regression analysis, and optimal threshold was calculated from ROC curves. The patients were divided into two groups using this threshold and progression-free survival was compared. Results: Among the 30 lesions, 16 recurrences were observed within one year after irradiation, while 9 lesions were well controlled for more than one year. Five lesions without recurrence were excluded because the follow-up period not reached one year. Met-uptake/BED was significantly correlated with the control of the lesion (p=0.020). The optimal threshold of Met-uptake/BED was calculated as 0.029. The progression-free survival time with low Met-uptake/BED (20.2m) was significantly longer than the others (4.4m, p=0.004). MGMTmethylation status also showed borderline significance, but the independent significance of Met-uptake/BED was ascertained with multivariate analysis (p=0.007). Required dose to control lesions could be decided upon the Met-PET using the following formula: BED= Metuptake/0.029. Conclusions: Required BED to control tumor was significantly correlated with the Met-uptake, and new treatment plan based upon Met-uptake was proposed. EP-1007 The nature of the failures in the complex treatment of ependymomas of the brain in children.