68(GA)DOTATATE PET-Based Radiation Volumes Demonstrate Increased Precision Compared to MRI Based Volumes for Meningioma Patients

Abstract

<h3>Purpose/Objective(s)</h3> Radiation treatment planning for meningioma conventionally involves MRI contrast enhanced images to define residual tumor. However, the gross tumor volume may be difficult to delineate for patients with a meningioma in the skull base, sagittal sinus, or post resection. Advanced PET imaging using 68(GA)DOTATATE PET, which has been shown to be more sensitive and specific than MRI imaging, can be used for target volume delineation in these circumstances. We hypothesize that 68(GA)DOTATATE PET scan-based treatment planning will lead to differences in radiation treatment volumes and will be more precise compared to standard MRI alone. <h3>Materials/Methods</h3> Our study evaluated retrospective, deidentified, and blinded gross tumor volume (GTV) contour delineation of 5 CNS specialists (3 neuroradiologists, 2 CNS radiation oncologists) for 26 patients diagnosed with a meningioma who received both a 68(GA)DOTATATE PET and an MRI for radiation treatment planning. Both the MRI and the PET-based GTV were non-sequentially contoured by each physician for each patient. We defined a significant difference in volume delineation if there was > 100% difference in contoured volume found for 80% of physicians or more when comparing MRI and PET. A PET only lesion was defined as any lesion not seen on MRI but delineated on PET imaging by at least 80% of physicians. This lesion would need to be non-adjacent to the MRI based contours for the same patient. <h3>Results</h3> The mean volume of MRI based contours was 12.5 ccs (range 0.55-62 ccs). The mean volume for PET directed contours was 13.7 ccs (range 0.24-94 ccs). We found 15/26 (58%) patients had at least a 100% difference in volume between PET and MRI for 80% of physician contours. 8/26 (31%) patients had new non-adjacent areas contoured on PET that were not contoured by these physicians on the corresponding MRI. These new areas would not have been in the traditional MRI based volumes. <h3>Conclusion</h3> We found a significant difference in PET based volumes with 58% showing major differences in volume and 31% showing new areas not seen on MRI. This has major implications on tumor control. Our study supports that 68(GA)DOTATATE PET imaging can help radiation oncologist be more precise with radiation treatment volumes. Utilization of 68(GA)DOTATATE PET may find undetected areas of disease which in turn can improve local control and progression free survival. 68(GA)DOTATATE PET guided treatment planning should be studied prospectively.