Introduction: Selective internal radiation therapy (SIRT) with SIR spheres (90Y microspheres) is a treatment option for liver tumours in patients in whom other therapies are inappropriate or have failed. This study aims to assess the value of FDG PET in assessing the response to SIRT as compared to computed tomography (CT).
Material and methods: Twenty-one patients (11 F, 10 M; age range 40-75 years, mean, 58 years) received SIR spheres at the Hammersmith Hospital. One patient received two treatments. Most patients had colorectal metastases (n=10), while the others (n=11) had liver metastasis from different primaries. The mean administered dose was 1.9 GBq (range, 1.2-2.5 GBq). Follow-up was done with FDG PET and CT at 6 weeks, and 6-monthly thereafter. Pre-therapy and post-therapy CT and PET scans were assessed visually (RECIST criteria for CT) and semi-quantitative for PET using the standardized uptake value (SUV).
Result: Eighty-six percent of patients showed decreased PET activity at 6 weeks while only 13% showed a partial response in the size of tumour on CT scan. The mean pre-treatment SUV was 12.2+/-3.7 and the mean post-treatment SUV was 9.3+/-3.7 (P=0.01). CT imaging showed progressive disease in 27% patients and stable liver disease in 60% patients. Based on FDG PET results one patient had surgery for down-staged tumour.
Conclusion: FDG PET imaging is more sensitive than CT in the assessment of early response to SIR spheres, allowing clinicians to proceed with further therapeutic options.