Potential impact of (68)Ga-DOTATOC PET/CT on stereotactic radiotherapy planning of meningiomas

Since meningiomas show a high expression of somatostatin receptor subtype 2, PET with (68)Ga-DOTATOC was proposed as an additional imaging modality beside CT and MRI for planning radiotherapy. We investigated the input of (68)Ga-DOTATOC-PET/CT on the definition of the "gross tumour volume" (GTV) in meningiomas, in order to assess the potential value of this method. Prior to radiotherapy, 42 patients with meningiomas (26 f, 16 m, mean age 55) underwent MRI and (68)Ga-DOTATOC-PET/CT examinations. operated n = 24, radiotherapy n = 1, operation and radiotherapy n = 8, no treatment n = 9. PET/CT and MRI data were co-registered using a BrainLAB workstation. For comparison, the GTV was defined first under consideration of CT and MRI data, then using PET data. 3/42 patients were excluded from the analysis (two with negative PET results, one with an extensive tumour, not precisely delineable by MRI or PET/CT). The average GTV(CT/MRI) was 22(+/-19)cm(3); GTV(PET) was 23(+/-20)cm(3). Additional GTV, obtained as a result of PET was 9(+/-10)cm(3) and was observed in patients with osseous infiltration. In some pre-treated patients there were intratumoural areas (as identified in CT/MRI) without SR-expression (7(+/-11)cm(3)). Common GTV as obtained by both CT/MRI and PET was 15(+/-14)cm(3). The mean bi-directional difference between the GTV(CT/MRI) and GTV(PET) accounted to 16(+/-15)cm(3) (93%, p < 0.001). In a subgroup of seven patients with multiple meningiomas, PET showed a total of 19 lesions; nine of them were not recognizable by CT or MRI. (68)Ga-DOTATOC-PET enables delineation of SR-positive meningiomas and delivers additional information to both CT and MRI regarding the planning of stereotactic radiotherapy. The acquisition on a PET/CT scanner helps to estimate the relation of PET findings to anatomical structures and is especially useful for detection of osseous infiltration. (68)Ga-DOTATOC-PET also allows detection of additional lesions in patients with multiple meningiomas.