Purpose: To investigate the potential impact of 68Ga-DOTATOC positron emission tomography (68Ga-DOTATOC-PET) in addition to magnetic resonance imaging (MRI) and computed tomography (CT) for retrospectively assessing the gross tumor volume (GTV) delineation of meningiomas of the skull base in patients treated with fractionated stereotactic radiation therapy (FSRT).
Methods and materials: The study population consisted of 48 patients with 54 skull base meningiomas, previously treated with FSRT. After scans were coregistered, the GTVs were first delineated with MRI and CT data (GTVMRI/CT) and then by PET (GTVPET) data. The overlapping regions of both datasets resulted in the GTVcommon, which was enlarged to the GTVfinal by adding volumes defined by only one of the complementary modalities (GTVMRI/CT-added or GTVPET-added). We then evaluated the contribution of conventional imaging modalities (MRI, CT) and 68Ga-DOTATOC-PET to the GTVfinal, which was used for planning purposes.
Results: Forty-eight of the 54 skull base lesions in 45 patients showed increased 68Ga-DOTATOC uptake and were further analyzed. The mean GTVMRI/CT and GTVPET were approximately 21 cm3 and 25 cm3, with a common volume of approximately 15 cm3. PET contributed a mean additional GTV of approximately 1.5 cm3 to the common volume (16%±34% of the GTVcommon). Approximately 4.5 cm3 of the GTVMRI/CT was excluded from the contribution to the common volume. The resulting mean GTVfinal was significantly smaller than both the GTVMRI/CT and the GTVPET. Compared with the initial GTVMRI/CT, the addition of 68Ga-DOTATOC-PET resulted in more than 10% modification of the size of the GTVfinal in 32 (67%) meningiomas
Conclusions: 68Ga-DOTATOC-PET/CT seems to improve the target volume delineation in skull base meningiomas, often leading to a reduction of GTV compared with results from conventional imaging (MRI and CT).
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