Dosimetric impact of clinical planning methodology for Yttrium-90 microsphere radioembolization

Some patients receive glass Yttrium-90 microsphere radioembolization for treatment of hepatocellular carcinoma. Traditional dosimetry uses a partition model to calculate doses to relevant structures, but this model has serious limitations; it assumes uniform perfusion and no cross-compartmental dose.

This work aims to assess several methods for performing dosimetry for these patients and compare them, with special attention paid to the differences of these methods from the partition model for the tumor, non-tumorous liver, and lungs. By performing this comparison, the partition model can be assessed for its shortcomings and dosimetric precision relative to other models.

Ten patients receiving ⁹⁰Y had their procedures simulated in Monte Carlo and doses tallied using three different source models, with two based on pre- and posttreatment imaging, and one meant to mimic the assumptions of the partition model.

When comparing mean dose within the prescribed tumor volume, the partition and pretreatment imaging models agreed to within 9.7%. Several patients showed lung doses above predicted doses from current standard practice, demonstrating the importance of cross-compartmental doses. Additionally, patients who received lobectomy often had high differential uptake of microspheres in the tumor, which were missed in prescription. However, the partition model missed high doses (> 20 Gy) to the stomach in two patients which were noted in simulation.

Overall, the partition model is appropriate for calculation of mean tumor doses if the information used in treatment planning is accurate, but caution should be used when calculating doses outside the liver, as cross-compartmental effects are often observed.