Feasibility of 90Y TOF PET-based dosimetry in liver metastasis therapy using SIR-Spheres.

(90)Y-labelled compounds used in targeted radiotherapy are usually imaged with SPECT by recording the bremsstrahlung X-rays of the beta decay. The continuous shape of the X-ray spectrum induces the presence of a significant fraction of scatter rays in the acquisition energy window, reducing the accuracy of biodistribution and of dosimetry assessments. The aim of this paper is to use instead the low branch of e(-) e(+) pair production in the (90)Y decay. After administration of (90)Y-labelled SIR-Spheres by catheterization of both liver lobes, the activity distribution is obtained by (90)Y time-of-flight (TOF) PET imaging. The activity distribution is convolved with a dose irradiation kernel in order to derive the regional dosimetry distribution. Evaluation on an anatomical phantom showed that the method provided an accurate dosimetry assessment. Preliminary results on a patient demonstrated a high-resolution absorbed dose distribution with a clear correlation with tumour response. This supports the implementation of (90)Y PET in selective internal radiation therapy of the liver.