A pilot study of [68Ga]Ga-DOTA-TATE PET-based radiation contouring for pituitary adenoma

Purpose: Radiation treatment planning for pituitary tumors traditionally involves magnetic resonance imaging (MRI) imaging. However, the gross tumor volume (GTV) may be difficult to delineate for patients after resection and recurrence. Advanced positron emission tomography (PET) imaging using [68Ga]Ga-DOTA-TATE has been used for somatostatin-expressing tumors, and can be used for target volume delineation. We hypothesized that [68Ga]Ga-DOTA-TATE PET scan - based GTV delineation would alter the target volume in comparison with MRI-based delineation. Methods and materials: This IRB-approved protocol retrospectively contoured GTVs for seven patients who had undergone [68Ga]Ga-DOTA-TATE PET for radiation treatment planning for pituitary tumors. Eligible patients had recurrent disease following at least one resection and underwent both MRI and PET for treatment planning. Four central nervous system radiation oncologists and one resident radiation oncologist contoured both the MRI and the PET nonsequentially for each patient. Results: The median MRI volume for each physician ranged from 4.41 to 7.19 cm3. The median PET volume for each physician ranged from 5.94 to 15.54 cm3. There was excellent interrater reliability, intraclass correlation coefficient was 0.95 for PET and 0.98 for MRI. There were no new nonadjacent areas of disease identified on PET or MRI. Average PET volumes were both larger and smaller than average MRI volumes for different patients. The range of differences between average MRI and PET volumes was (−3.81 cm3 – +4.34 cm3). There was a median absolute difference between average PET and average MRI volume of 2.24 cm3, which corresponds to a median relative percent difference of 20.3%. Conclusions: These results support the conclusion that [68Ga]Ga-DOTA-TATE PET alters treatment volumes in radiation planning for recurrent pituitary tumors. Whether PET imaging changes treatment outcomes is unknown. The use of this imaging modality for pituitary radiation planning should be studied prospectively.