Abstract
Simple SummaryMeningiomas are the most frequent tumors of the central nervous system. Their treatment outcomes depend on the histologic grade. Grade I tumors, even bulky and unresectable, are well curable with radiation; therefore, most precise and conservative techniques such as proton therapy are utilized. To better distinguish between tumor extent and normal tissues, PET/CT using tracers that bind specifically to somatostatin receptor type 2 (SSTR2), commonly expressed by these tumors, can be used in addition to MRI. In an experimental blinded study of 30 pre-operated WHO grade I meningiomas independently delineated by four radiation oncologists, we confirmed that the overwhelming majority of meningiomas do express SSTR2 and that the addition of receptor-targeted PET/CT helps visualize lesions not unanimous in MRI and improves the homogeneity of tumor volume definition between observers. SSTR2-targeted PET/CT should be a standard in the planning of curative radiation in pre-operated meningioma.Grade I meningioma is the most common intracranial tumor in adults. The standard imaging for its radiation treatment planning is MRI, and [68Ga]1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA)-conjugated PET/CT can further improve delineation. We investigated the impact of PET/CT on interobserver variability in identifying the tumor in 30 anonymized patients. Four radiation oncologists independently contoured residual tumor volume, first using only MRI and subsequently with the addition of PET/CT. Conformity indices (CIs) were calculated between common volumes, observer pairs and compared to the volumes previously used. Overall, 29/30 tumors (96.6%) showed [68Ga]Ga-DOTA avidity. With help of PET/CT, the participants identified six cases with new lesions not recognized in MRI, including two where new findings would critically alter the target volume used for radiation. The PET/CT-aided series demonstrated superior conformity, as compared to MRI-only between observer pairs (median CI = 0.58 vs. 0.49; p = 0.002), common volumes (CI = 0.34; vs. 0.29; p = 0.002) and matched better the reference volumes actually used for patient treatment (CI = 0.55 vs. 0.39; p = 0.008). Cis in the PET/CT-aided series were lower for meningiomas outside of the skull base (0.2 vs. 0.44; p = 0.03). We conclude that SSTR2 receptor-targeted PET/CT is a valuable tool for planning particle therapy of incompletely resected meningioma. It serves both as a workup procedure and an aid for delineation process that reduces the likelihood of marginal misses.
Highlights
Meningioma, a tumor originating from the cells of meninges, is the most common intracranial neoplasm in humans
In 6 (20.6%) of the remaining 29 cases, PET/CT revealed new findings not unanimously identifiable in MRI-only based assessment. Three of these (10.3%) corresponded to additional small peripheral meningiomas of the falx, and in one case, the new finding was an asymptomatic intraosseous extension in a patient irradiated for a meningioma of the falx
These were interpreted as coincidental findings distant from the actual target volume, and their management was concluded to be watchful waiting with resection or irradiation seeming feasible in case of radiologic and/or symptomatic progression
Summary
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