MIRD Pamphlet No. 29: MIRDy90-A 90Y Research Microsphere Dosimetry Tool

Abstract

⁹⁰Y-microsphere radioembolization has become a well-established treatment option for liver malignancies and is one of the first U.S. Food and Drug Administration-approved unsealed radionuclide brachytherapy devices to incorporate dosimetry-based treatment planning. Several different mathematical models are used to calculate the patient-specific prescribed activity of ⁹⁰Y, namely, body surface area (SIR-Spheres only), MIRD single compartment, and MIRD dual compartment (partition). Under the auspices of the MIRDsoft initiative to develop community dosimetry software and tools, the body surface area, MIRD single-compartment, MIRD dual-compartment, and MIRD multicompartment models have been integrated into a MIRDy90 software worksheet. The worksheet was built in MS Excel to estimate and compare prescribed activities calculated via these respective models. The MIRDy90 software was validated against available tools for calculating ⁹⁰Y prescribed activity. The results of MIRDy90 calculations were compared with those obtained from vendor and community-developed tools, and the calculations agreed well. The MIRDy90 worksheet was developed to provide a vetted tool to better evaluate patient-specific prescribed activities calculated via different models, as well as model influences with respect to varying input parameters. MIRDy90 allows users to interact and visualize the results of various parameter combinations. Variables, equations, and calculations are described in the MIRDy90 documentation and articulated in the MIRDy90 worksheet. The worksheet is distributed as a free tool to build expertise within the medical physics community and create a vetted standard for model and variable management.

Keywords: 90Y-microspheres; MIRD dual-compartment dosimetry; partition model dosimetry; radioembolization; selective internal radiation therapy (SIRT).

FIGURE 1.

Summary of various ⁹⁰Y prescription activity models with associated compartments and assumed distribution. (A) Ground truth sphere distribution. (B) BSA model—considers volumes of 3 regions, including tumor, perfused liver, and whole liver volumes. (C) MIRD single compartment—considers only target region volume. (D) MIRD dual compartment—considers perfused normal-liver region volume and tumoral liver volume. (E) MIRD multicompartment—considers perfused normal-liver region volume, tumoral liver volume, and individual tumor volumes. (F) Voxel-level distribution.

FIGURE 2.

Screenshot of MIRDy90 software graphical user interface. User input area is on left, and worksheet calculations are on right. In this example, MIRD dual-compartment model is selected, and target absorbed dose is prescribed to achieve 205 Gy to tumor. (A) Input data fields for each model. Input parameters used in selected model are highlighted. (B) Model summary box, which displays user’s selected calculation outputs. (C) Selected model graphical display and dose summary table. (D) MIRD dual-compartment dosimetry model outputting display activity and absorbed dose summaries for each of 4 prescribed activity targets. (E) MIRD multicompartment input (TNR_i) and projected tumor-absorbed doses (for up to 5 tumors) (optional). (F) Single-compartment (MIRD) and BSA dosimetry model outputs providing conventional model summaries. DL = dose limit; PNL = perfused normal liver.

FIGURE 3.

MIRDy90—selecting prescribed activity calculation model.