The Value of SSTR2 Receptor-Targeted PET/CT in Proton Irradiation of Grade I Meningioma

Abstract

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.

The Role of [68Ga]Ga-DOTA-SSTR PET Radiotracers in Brain Tumors: A Systematic Review of the Literature and Ongoing Clinical Trials

“…The authors compared planning target volumes (PTVs) on fused PET to those on CT/MRI only, reporting improved PTV delineation in 73% of patients after PET-fused planning, which better identified the transosseous extent of meningiomas. Comparable results were also obtained in other studies, which further reported [ 68 Ga]Ga-DOTA-SSTR PET detection of additional information on meningiomas not detected at MRI [ 28 , 69 ] and superior target delineation of post-surgery/radiation meningioma recurrence from post-treatment tissue scarring or edema/pseudoprogression [ 27 , 29 ]. The role of [ 68 Ga]Ga-DOTA-SSTR PET for tumor volume contouring has been validated for FSRT [ 20 , 66 ], radiosurgery [ 17 , 18 ], and proton/carbon therapy [ 32 , 69 ] planning, optimizing PTV delineation, improving target dose escalation, and minimizing radiation to organs at risk, especially for the highly challenging optic nerve sheath meningiomas [ 18 ].…”

“…Comparable results were also obtained in other studies, which further reported [ 68 Ga]Ga-DOTA-SSTR PET detection of additional information on meningiomas not detected at MRI [ 28 , 69 ] and superior target delineation of post-surgery/radiation meningioma recurrence from post-treatment tissue scarring or edema/pseudoprogression [ 27 , 29 ]. The role of [ 68 Ga]Ga-DOTA-SSTR PET for tumor volume contouring has been validated for FSRT [ 20 , 66 ], radiosurgery [ 17 , 18 ], and proton/carbon therapy [ 32 , 69 ] planning, optimizing PTV delineation, improving target dose escalation, and minimizing radiation to organs at risk, especially for the highly challenging optic nerve sheath meningiomas [ 18 ]. Likewise, d’Amico et al [ 36 ] confirmed the potential benefits of using [ 68 Ga]Ga-DOTA-SSTR PET for radiosurgery planning in pituitary carcinomas infiltrating the cavernous sinus, as it allows precise tumor contouring of residual post-surgery volumes.…”

“…DOTATOC was the most frequent tracer used overall (total: 548 patients, 53.2%), but DOTATATE was used more in patients undergoing diagnostic [ 68 Ga]Ga-DOTA-SSTR PET studies (329, 51.1%). Purandare et al [ 54 ] described the use of DOTANOC tracer in 40 patients to differentiate meningiomas from dural-based brain metastases, and Pelak et al [ 69 ] to delineate tumor volumes for proton therapy in 19 patients with grade-1 meningiomas. Seysthal et al [ 21 ] lacked a clear distinction in the use of DOTATOC or DOTATATE, grouping all 20 of their patients in a single DOTATOC/DOTATATE group.…”

“…All lesions were meningiomas (99.7%), except for one pituitary carcinoma reported by d’Amico et al [ 36 ]. DOTATOC (78.2%) was utilized more frequently than DOTATATE (21.8%), and Pelak et al [ 69 ] also reported the use of DOTANOC in 19 patients. [ 68 Ga]Ga-DOTA-SSTR PET studies were mostly fused with CT/MRI studies and implemented to improve volume contouring for radiation planning, such as stereotactic radiotherapy (SRT) [ 20 , 26 , 28 , 33 ], intensity-modulated radiotherapy (IMRT) [ 27 , 29 ], conventional radiotherapy [ 46 , 49 , 51 , 66 ], cyber knife radiosurgery (CKRS) [ 17 , 18 ], and carbon/proton therapy [ 32 , 69 ].…”

“…DOTATOC (78.2%) was utilized more frequently than DOTATATE (21.8%), and Pelak et al [ 69 ] also reported the use of DOTANOC in 19 patients. [ 68 Ga]Ga-DOTA-SSTR PET studies were mostly fused with CT/MRI studies and implemented to improve volume contouring for radiation planning, such as stereotactic radiotherapy (SRT) [ 20 , 26 , 28 , 33 ], intensity-modulated radiotherapy (IMRT) [ 27 , 29 ], conventional radiotherapy [ 46 , 49 , 51 , 66 ], cyber knife radiosurgery (CKRS) [ 17 , 18 ], and carbon/proton therapy [ 32 , 69 ]. The implementation of [ 68 Ga]Ga-DOTA-SSTR PET proved to significantly improve target definition in meningiomas of the skull base, parafalcine, intraosseous, or affecting the optic nerve sheath, also favoring reduced radiation doses to adjacent organs at risk.…”