Author: Wesley E. Bolch, Chansoo Choi, Robert Joseph Dawson, Michael Lassmann, Maikol Salas-Ramirez, Bangho Shin, Johannes Tran-Gia, Yitian Wang 👨🔬
Affiliation: Department of Nuclear Medicine, University Hospital Würzburg, University of Florida 🌍
Purpose: Conduct a parameterized library of mesh-type skeletal models across the lumbar vertebrae. In radiopharmaceutical dosimetry, the hematopoietic active bone marrow is typically a dose-limiting normal organ which thus limits level of activity administered to cancer patients. To assess the radiation dose to active marrow, serial 3D imaging of lumbar vertebrae is conducted to compute time-activity curves, with radionuclide S-values from “reference individuals” applied. However, for personalized active marrow dose calculations, key factors like skeletal size, trabecular bone volume fraction (TBVF), and marrow cellularity may differ from the “reference individuals”. This study generates a comprehensive series of mesh-type L-series skeletal models to enable refined and patient-informed dosimetry.
Methods: The specific skeletal models incorporate four microstructures: trabecular bone, bone endosteum, adipocytes (representing inactive marrow), and hematopoietic tissues (representing active marrow). This study focused on the adult female lumbar vertebrae, with some adult male data included for comparison. These models were derived from reference skeletal models and include variations in (1) skeletal size, (2) TBVF, and (3) marrow cellularity. Clinical data guide the variation in TBVF, ranging from 5% to 25% in 5% increments, and cellularity, ranging from 0% to 100% in 10% increments. Model generation was performed by an 3D rendering software and in-house C++ program, and dosimetry analysis was conducted using the Particle and Heavy Ion Transport code System (PHITS) for various radionuclides S-values.
Results: The study considered five skeletal sites (L1–L5) for adult females and one skeletal site (L2) for adult males. 360 specific skeletal models were developed. S-values for radiation dose distributions across the models were obtained using several radionuclides, including Lu-177.
Conclusion: The microscale skeletal models are developed to provide a more accurate and comprehensive method for evaluating skeletal dosimetry across diverse populations. These models have applications in various fields, including radiopharmaceutical dosimetry and radiological protection.