68Ga-DOTATOC PET/CT in the monitoring of 90Y-DOTATOC treatment

Objectives Aim of this study is to evaluate the role of ⁶⁸Ga-DOTATOC PET/CT in monitoring the radiolabelled somatostatin analog ⁹⁰Y-DOTA-D-Phe¹-Tyr³-octreotide (⁹⁰Y-DOTATOC) treatment.

Methods Forty patients (pts), m/f 20/20, age 32-83 yrs, mean 66 yrs, with metastatic somatostatin-receptor-positive tumors, were treated with ⁹⁰Y-DOTATOC (31 NETs, 4 radioiodine negative differentiated thyroid carcinoma, 4 small-cell lung carcinoma, 1 breast cancer). Pts underwent ⁶⁸Ga-DOTATOC PET/CT before therapy and 2 months after each treatment. PET studies were compared by visual and SUV analysis. Response was documented also by clinical and biochemical findings. Treatment was once every 3 months.

Results Two pts had 6 treatments, 13 pts 5, 5 pts 4, 3 pts 3, 10 pts 2 and 7 pts 1. The responses were as follows: 18% progression disease, 43% stable disease, 21% partial response and 3% complete response; in 6 pts (15%) the evaluation is in progress. The clinical response resulted higher than biochemical and PET/CT findings. The PET/CT improvement was superior in liver metastases than in other tissues. SUV tumor/non-tumor ratio performed better than SUV alone; the site for the reference ROI was the muscle tissue of the supracetabular region. The case with complete response was documented by PET after the first treatment.

Conclusions Radiolabelled somatostatin analogs therapy is very promising. ⁶⁸Ga-DOTATOC PET/CT is useful in pts selection and treatment monitoring. Further investigations are necessary to evaluate the appropriate timing of PET during therapy.