Tumor shrinkage assessed by volumetric MRI in the long-term follow-up after stereotactic radiotherapy of meningiomas.

PURPOSE: To evaluate tumor volume reduction in the follow-up of meningiomas after fractionated stereotactic radiotherapy (FSRT) or linac radiosurgery (RS) by using magnetic resonance imaging (MRI). PATIENTS AND METHODS: In 59 patients with skull base meningiomas, gross tumor volume (GTV) was outlined on contrast-enhanced MRI before and median 50 months (range 11-92 months) after stereotactic radiotherapy. MRI was performed as an axial three-dimensional gradient-echo T1-weighted sequence at 1.6 mm slice thickness without gap (3D-MRI). Results were compared to the reports of diagnostic findings. RESULTS: Mean tumor size of all 59 meningiomas was 13.9 ml (0.8-62.9 ml) before treatment. There was shrinkage of the treated meningiomas in all but one patient. Within a median volumetric follow-up of 50 months (11-95 months), an absolute mean volume reduction of 4 ml (0-18 ml) was seen. The mean relative size reduction compared to the volume before radiotherapy was 27% (0-73%). Shrinkage measured by 3D-MRI was greater at longer time intervals after radiotherapy. The mean size reduction was 17%, 23%, and 30% (at < 24 months, 24-48 months, and 48-72 months). CONCLUSION: By using 3D-MRI in almost all patients undergoing radiotherapy of a meningioma, tumor shrinkage is detected. The data presented here demonstrate that volumetric assessment from 3D-MRI provides additional information to routinely used radiologic response measurements. After FSRT or RS, a mean size reduction of 25-45% can be expected within 4 years.

Effect of 11C-methionine-positron emission tomography on gross tumor volume delineation in stereotactic radiotherapy of skull base meningiomas.

PURPOSE: To evaluate the effect of trimodal image fusion using computed tomography (CT), magnetic resonance imaging (MRI) and (11)C-methionine positron emission tomography (MET-PET) for gross tumor volume delineation in fractionated stereotactic radiotherapy of skull base meningiomas. PATIENTS AND METHODS: In 32 patients with skull base meningiomas, the gross tumor volume (GTV) was outlined on CT scans fused to contrast-enhanced MRI (GTV-MRI/CT). A second GTV, encompassing the MET-PET positive region only (GTV-PET), was generated. The additional information obtained by MET-PET concerning the GTV delineation was evaluated using the PET/CT/MRI co-registered images. The sizes of the overlapping regions of GTV-MRI/CT and GTV-PET were calculated and the amounts of additional volumes added by the complementing modality determined. RESULTS: The addition of MET-PET was beneficial for GTV delineation in all but 3 patients. MET-PET detected small tumor portions with a mean volume of 1.6 +/- 1.7 cm(3) that were not identified by CT or MRI. The mean percentage of enlargement of the GTV using MET-PET as an additional imaging method was 9.4% +/- 10.7%. CONCLUSIONS: Our data have demonstrated that integration of MET-PET in radiotherapy planning of skull base meningiomas can influence the GTV, possibly resulting in an increase, as well as in a decrease.