Objectives: The aim of this study is to analyze precision and usefulness of (68)Ga-DOTATATE PET/CT images compared with CT/MR for contouring tumor margins of meningiomas treated by stereotactic radiosurgery.

Methods: Clinical material consists of 74 meningioma tumors in 59 patients treated in a single institution by stereotactic radiosurgery using CyberKnife during 2012-1016. Tumor margins were delineated twice by four independent planners. At first using CT/MF fusion, and by (68)Ga-DOTATATE PET/CT fusion thereafter. Final contours were defined as a sum of both products (Boolean OR operator). For PET/CT contouring the threshold SUV limit values of 0-100%, 25-100%, 50-100% and 75-100% of the maximum SUV were tested. Correlation between tumor volumes defined by CT/MR and CT/PET (for each SUV limit) and Conformity Indexes were estimated and compared. Radiotherapy Teatment Planning (TPS) was performed on MultiPlan CyberKnife System.

Results: Correlation coefficient for CT/MR vs. CT/PET target margins drawn by physicist was r=0.75 for SUV limit 0-100%, and 0.91, 0.82, 0.51 for SUV limit of 25-100%, 50-100% and 75-100% respectively. Use of PET/CT imaging with SUV limit 25-100% is characterized by the highest Correlation Coefficient of r=0.91 and Conformity Index of CI=0.52±0.16.

Conclusions: Among four tested values of the SUV limit, correlation between margins estimates and the SUV limits was the highest for 25-100% SUVmax. It means that the contour drawn with 25% treshold value of the SUV give the best fit compared with MR/CT contours. Therefore this threshold seems to be optimal for contouring the meningiomas using (68)Ga-DOTATATE PET/CT images.