Program Information
Split-Dose Y-90 Microsphere Therapy: Does a Single Tc-99m MAA Mapping Study Suffice?
M Vanderhoek1*, (1) Henry Ford Health System, Detroit, MI
Presentations
SU-E-708-4 (Sunday, July 30, 2017) 1:00 PM - 1:55 PM Room: 708
Purpose: Treatment of hepatic malignancies with Y-90 microsphere therapy can require a “split-dose” where 2 liver sub-volumes are treated with separate vials of microspheres. Ideally, 2 separate pre-treatment Tc-99m-MAA mapping studies (1 per sub-volume) should be acquired. However, treatment planning dosimetry is typically based on a single mapping study of both sub-volumes. We investigated the dosimetric uncertainties associated with a “split-dose” planned from a single Tc-99m-MAA mapping study.
Methods: A standard partition model was used to plan treatment doses to liver sub-volumes (VolA, VolB) and to the lungs, using a single Tc-99m-MAA mapping study. Dosimetry was determined for different mapping scenarios: equal Tc-99m-MAA activities (Scenario 1) vs. equal Tc-99m-MAA activity concentrations (MBq/mL of tissue, Scenario 2) administered to sub-volumes. Dosimetric uncertainties due to variation in lung shunting from the sub-volumes were determined for cases with moderate (10%) and high (20%) lung shunting and for cases with equal (VolA=VolB) and unequal sub-volumes (VolA/VolB=2). Uncertainties were quantified via the range of possible doses to the sub-volumes (RangeA, RangeB) and to the lungs (RangeLung), expressed as a percentage of the planned dose.
Results: With a single mapping study, dosimetric uncertainties stem from uncertainty on the source of lung shunting, as it may be from only one or both liver sub-volumes. Cases with high lung shunting and unequal sub-volumes resulted in substantial uncertainties on sub-volume doses (Scenario 1: RangeA=50%, RangeB=50%; Scenario 2: RangeA=37%, RangeB=75%). In these cases, there was substantial uncertainty on lung dose for Scenario 1 (RangeLung=66%) but no uncertainty for Scenario 2 (RangeLung=0%). Overall, dosimetric uncertainties were reduced for cases with moderate lung shunting and/or equal sub-volumes.
Conclusion: Substantial dosimetric uncertainties can arise when “split-dose” Y-90 therapy is planned based upon a single Tc-99m-MAA mapping study. Dual mapping studies may be warranted in cases with high lung shunting and/or unequal liver sub-volumes.
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