IMG-42. Contribution of 18F-FDOPA PET imaging for target volume delineation in stereotactic radiosurgery treatment planning for brain metastasis: a pilot study

Abstract Positron emission tomography (PET) has become an important imaging test in the diagnosis of brain tumors. Amino acid and amino acid analog PET tracers, including 18F-FET, 11C-MET and 18F-FDOPA, are particularly attractive for imaging of brain tumors. The purpose of this study was to investigate the potential impact of 18F-FDOPA PET in addition to magnetic resonance imaging (MRI) for retrospectively assessing the target volume of brain metastases in patients treated with stereotactic radiosurgery (SRS) This study consisted of 28 patients with brain metastasis. This cohort study consisted of 13 male and 15 female patients. The median age was 55.6 years (range, 22–71). After scans were coregistered, the gross tumor volume (GTV)s were first delineated with MRI data (GTV-MRI) and then by 18F-FDOPA PET (GTV-PET) data. The overlapping regions of both datasets resulted in the GTV-common, which was enlarged to the GTV-final by adding volumes defined by only one of the complementary modalities (GTV-MRI/CT-added or GTV-PET-added). We then evaluated the contribution of MRI and 18F-FDOPA-PET to the GTV-final. The mean GTV-MRI and GTV-PET were approximately 3.28 cm3 and 2.91 cm3, with a common volume of approximately 2.22 cm3. PET contributed a mean additional GTV of approximately 0.32 cm3 to the common volume. Approximately 0.79 cm3 of the GTVMRI was excluded from the contribution to the common volume. Compared with the initial GTVMRI, the addition of 18F-FDOPA-PET resulted in more than 10% modification of the size of the GTVfinal in 20 (71%) patients. However, there was no significant difference between the GTV-final and the GTV-MRI and the GTV-PET. 18F-FDOPA-PET seems to improve the target volume delineation in brain metastases, often leading to a reduction of GTV compared with results from conventional imaging (MRI and CT).