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

Abstract
Purpose 90Y-labelled compounds used in targeted radiotherapy are usually imaged with SPECT by recording the bremsstrahlung X-rays of the β 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. Methods The aim of this paper is to use instead the low branch of e− e+ pair production in the 90Y decay. After administration of 90Y-labelled SIR-Spheres by catheterization of both liver lobes, the activity distribution is obtained by 90Y time-of-flight (TOF) PET imaging. The activity distribution is convolved with a dose irradiation kernel in order to derive the regional dosimetry distribution. Results 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. Conclusion This supports the implementation of 90Y PET in selective internal radiation therapy of the liver.