Treatment > Radiotherapy  

Abstract

C11-methionine PET in radiotherapy planning of glioma

A. L. Grosu, W. A. Weber, R. Lachner, N. Wiedemann, C. Nieder, E. Mergen, M. Schwaiger, M. Molls

Klinikum rechts der Isar, Techn. University Munich, Munich, Germany; BrainLAB, Munich, Germany

Purpose. Using magnetic resonance tomography (MRT) and computed tomography (CT), residual tumor cannot be differentiated from non-specific postoperative changes in patients with glioma after surgical resection.
Our goal was to analyse the value of carbon-11 methionine positron emission tomography (MET-PET) in residual tumor delineation for patients with glioma selected for dose escalation.

Materials and Methods. In 30 patients with resected glioblastoma MET-PET, CT and MRT were performed for planning of radiation dose escalation using stereotactic radiotherapy.
The MET-PET data were integrated in the BrainLAB planning system and were co-registrated with the CT and MRT data using automatically intensity-based image fusion.
The patients were treated initially with a total dose of 60 Gy.
The dose was escalated using stereotactic radiotherapy by delivering an additional 20 Gy in 5 Gy/fraction.
The planning target volume (PTV) for dose escalation corresponded to the gross tumor volume (GTV) and encompassed the MET uptake in the MET-PET/CT/MRT fusion images (GTV-PET).
The GTV-MET was compared with the GTV defined using the T1-weighted MRT with gadolinium (GTV-MRT).

Results. The GTV-PET corresponded to the GTV-MRT in 11/30 patients.
In 19/30 patients the contrast-enhancement in MRT was located also outside of the areas with MET uptake in PET.
In 15/30 patients MET uptake was outlined in areas without contrast-enhancement in T1-MRT.
The mean GTV-PET and GTV-MRT were 7.4 ccm and 13.1 ccm, respectively.
The mean volume encompassing both MET and gadolinium (Gd) enhancement (common GTV-PET/MRI) was 4.6 ccm.
The mean volume of Gd enhancement without changes in MET-PET was 8.5 ccm (Vol-Gd only).
The mean volume including the MET uptake in PET, without Gd-enhancement in T1-MRT was 2.8 ccm.

Conclusion. In operated patients with brain glioma the size and location of residual MET uptake differs considerably from abnormalities in postoperative MRT. Because of the known high specificity of MET-uptake for tumor tissue the findings in MET-PET may significantly modify target volumes for radiation treatment planning.
This helps to focus the high irradiation dose on the tumor area and to spear normal issue.

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