Impact of 68Ga-DOTATOC PET/MRI on robotic radiosurgery treatment planning in meningioma patients: first experiences in a single institution

OBJECTIVE For stereotactic radiosurgery (SRS) planning, precise contouring of tumor boundaries and organs at risk is of utmost importance. Correct interpretation of standard neuroimaging (i.e., CT and MRI) can be challenging after previous surgeries or in cases of skull base lesions with complex shapes. The aim of this study was to evaluate the impact of Ga-68-DOTATOC PET/MRI on treatment planning for image-guided SRS by CyberKnife. METHODS The authors retrospectively identified 11 meningioma treatments in 10 patients who received a Ga-68-DOTATOC PET/MRI prior to SRS. The planning target volume (PTV) used for the patients' treatment was defined as the reference standard. This was contoured by a treating radiosurgeon (RSO) using fused planning CT and PET/MRI data sets. The same tumors were then contoured by another experienced radiosurgeon (RS1) and by a less-experienced radiosurgeon (RS2), both blinded to PET data sets. A comparison of target volumes with focus on volume-based metrics and distance to critical structures was performed. RS1 and RS2 also filled in a questionnaire analyzing the confidence level and the subjective need for the implementation of PET data sets for contouring. RESULTS Analysis showed a subjective personal preference for PET/MRI in all cases for both radiosurgeons, particularly in proximity to critical structures. The analysis of the planning volumes per physician showed significantly smaller RS2-PTV in comparison to RS1-PTV and to RS0-PTV, whereas the median volumes were comparable between RS1-PTV and RS2-PTV (median: RS0: 4.3 cm(3) [IQR 3.4-6.5 cm(3)] and RS1: 4.5 cm(3) [IQR 2.7-6 cm(3)] vs RS2: 2.6 cm(3) [IQR 2-5 cm(3)]; p = 0.003). This was also reflected in the best spatial congruency between the 2 experienced physicians (RS0 and RS1). The percentage of the left-out volume contoured by RS1 and RS2 compared to RS0 with PET/MRI demonstrated a relevant left-out-volume portion in both cases with greater extent for the less-experienced radiosurgeon (RS2) (RS1: 19.1% [IQR 8.5%-22%] vs RS2: 40.2% [IQR 34.2%-53%]). No significant differences were detected regarding investigated critical structures. CONCLUSIONS This study demonstrated a relevant impact of PET/MRI on target volume delineation of meningiomas. The extent was highly dependent on the experience of the treating physician. This preliminary study supports the relevance of Ga-68-DOTATOC PET/MRI as a tool for radiosurgical treatment planning of meningiomas.