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

Purpose: (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.

Methods: 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.

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 (90)Y PET in selective internal radiation therapy of the liver.