[Ga]-DOTATATE PET/MRI as an adjunct imaging modality for radiation treatment planning of meningiomas.

Background: Meningiomas express high levels of somatostatin receptor 2 (SSTR2). SSTR2-targeted PET imaging with [Ga]-DOTATATE can aid with distinguishing residual meningioma from reactive changes in the postoperative setting. We present initial dosimetric analyses, acute events, and local control data utilizing [Ga]-DOTATATE PET/MRI-assisted target delineation for prospectively-treated intermediate-risk meningiomas.

Methods: Twenty-nine patients underwent DOTATATE PET/MRI meningioma evaluation in 2019. Eight patients with 9 postoperative meningiomas met RTOG 0539 intermediate-risk criteria (recurrent WHO grade I, 1/9; WHO grade II, 8/9). Target volumes were created using DOTATATE PET/MRI to determine residual disease and received a nominal dose of 35.0 Gy over 5 fractions. For comparison, cases were recontoured and planned with MRI alone per RTOG 0539 guidelines. Mean and maximum equivalent 2 Gy doses were generated for target volumes and organs at risk (OAR) within 1 cm of the PTV and compared using Wilcoxon matched pairs signed rank test.

Results: DOTATATE PET/MRI-guided planning significantly reduced mean PTV (11.12 cm compared to 71.39 cm based on MRI alone, < .05) and mean and max dose to the whole brain, optic nerves, and scalp. PET/MRI plans resulted in at least 50% reduction of mean and max doses to the lens, eyes, chiasm, cochlea, brainstem, and hippocampi. One patient experienced focal alopecia. There were no local recurrences at 6 months.

Conclusion: Incorporating DOTATATE-PET/MRI for postoperative target delineation in patients with intermediate-risk intracranial meningiomas results in PTV reduction and decreased OAR dose. Our findings warrant larger studies evaluating DOTATATE-PET/MRI in the radiotherapeutic planning of postoperative meningiomas.