SPECT- and MR-primed microspheres track radioembolization
Quantitative imaging with either SPECT or MR reveals the path of microspheres following liver radioembolization and could one day predict success of therapy, according to a study published Oct. 17 in the Journal of Nuclear Medicine.
Radioembolization is an interventional therapy whereby radioactive materials, in this case Holmium-poly(L-lactic acid) microspheres as small as 20 microns, are used to block arteries providing vital blood supply to tumors. A team of researchers including Maarten L.J. Smits, MD, a radiologist from the University Medical Center Utrecht, The Netherlands, evaluated companion diagnostics with SPECT and MR and their ability to assess the impact of radioembolization in this first-ever phase I clinical trial.
“Using Ho-166 microspheres, in vivo dosimetry based on SPECT and MR imaging correlated well for dose to liver segments and dose to tumors,” wrote Smits et al. “These results may enable personalized treatment by selective targeting of inadequately treated tumors.”
For this study, 15 patients ineligible for surgery with chemo-resistant liver metastases underwent Ho-166 liver radioembolization. Liver and tumor segmentation were manually delineated on T2-weighted MR images co-registered after the fact with SPECT, SPECT/CT or MR imaging–based reference maps. In 40 percent of patients, agent uptake in all tumors was equal or higher to concentrations in normal liver. A quantitative analysis revealed the median overall tumor to nontumor ratio to be the same (1.4) for both SPECT and MR imaging.
“These next-generation microspheres for radioembolization are therapeutic and imaging agents in one and provide the opportunity to see what one is treating,” wrote the authors. “Suboptimal treatment can be detected by MR imaging and SPECT, and a pretreatment plan can be elaborated to ensure the full efficacy of the treatment.”
The next phase of research will determine if a pretreatment “scout dose” of Ho-166 microspheres could predict success of therapy in order to tailor dosage and biodistribution and prevent unnecessary treatment for patients who are unlikely to respond to therapy.