The use of 90Y-PET imaging in evaluation of 90Y-microspheres distribution in the liver: initial results.

BACKGROUND: Selective internal radiation therapy (SIRT) with 90Y-microspheres infusion into the hepatic artery is a novel method for palliative treatment of primary and metastatic liver cancer. The post-procedural 90Y dose estimation in the liver is very difficult because direct measurement of b particles is not possible with SPECT/CT. New methods are needed to assess the 90Y-microspheres liver distribution. In the present paper we evaluate the 90Y-PET for these purposes. MATERIALS AND METHODS: A GE Discovery ST PET/CT scanner with a copper ring protected the gantry was used for images acquisition. For SPECT/CT imaging, a GE Infinia VCHWK4 with HEPG collimators was used. The liver 90Y-microspheres (SIR-Spheres, SIRTEX, Australia) dose distribution after selective internal radiotherapy treatment was evaluated in three patients (9 lesions in total). The activity of 90Y-microspheres delivered into the liver ranged from 1.0 GBq to 2.2 GBq. The correlations between liver lesions detected with 90Y-PET, 99mTc-MAA and 90-bremsstrahlung were investigated and compared with CT images obtained before and after the procedure. RESULTS: The mean T/N ratio was 2.7 in 99mTc-MAA, 2.3 in 90Y-bremsstrahlung and 3.6 in 90Y-PET. The mean 90Y absorbed dose in tumor was 133 Gy, 112 Gy, and 187 Gy, respectively. The mean liver tissue radiation was 15.5 Gy. According to RECIST criteria, one PR (mCRC) and two SD were observed (mCRC and PC). Time to progression was 217 and 117 days in two patients with mCRC and 214 days in the patient with PC. CONCLUSIONS: 90Y-PET/CT images give crucial information regarding 90Y-microspheres distribution and dosimetry and may serve as a predictor of efficiency of radioembolisation.