Three-Dimensional Radiobiologic Dosimetry: Application of Radiobiologic Modeling to Patient-Specific 3-Dimensional Imaging-Based Internal Dosimetry

Abstract

MarylandPhantom-based and patient-specific imaging-based dosimetry methodologies have traditionally yielded mean organ-absorbed doses or spatial dose distributions over tumors and normal organs. In this work, radiobiologic modeling is introduced to convert the spatial distribution of absorbed dose into biologically effective dose and equivalent uniform dose parameters. The methodology is illustrated using data from a thyroid cancer patient treated with radioiodine. Methods: Three registered SPECT/CT scans were used to generate 3-dimensional images of radionuclide kinetics (clearance rate) and cumulated activity. The cumulated activity image and corresponding CT scan were provided as input into an EGSnrc-based Monte Carlo calculation: The cumulated activity image was used to define the distribution of decays, and an attenuation image derived from CT was used to define the corresponding spatial tissue density and composition distribution. The rate images were used to convert the spatial absorbed dose distribution to a biologically effective dose distribution, which was then used to estimate a single equivalent uniform dose for segmented volumes of interest. Equivalent uniform dose was also calculated from the absorbed dose distribution directly. Results: We validate the method using simple models; compare the dose-volume histogram with a previously analyzed clinical case; and give the mean absorbed dose, mean biologically effective dose, and equivalent uniform dose for an illustrative case of a pediatric thyroid cancer patient with diffuse lung metastases. The mean absorbed dose, mean biologically effective dose, and equivalent uniform dose for the tumor were 57.7, 58.5, and 25.0 Gy, respectively. Corresponding values for normal lung tissue were 9.5, 9.8, and 8.3 Gy, respectively. Conclusion: The analysis demonstrates the impact of radiobiologic modeling on response prediction. The 57% reduction in the equivalent dose value for the tumor reflects a high level of dose nonuniformity in the tumor and a corresponding reduced likelihood of achieving a tumor response. Such analyses are expected to be useful in treatment planning for radionuclide therapy.Key Words: dosimetry; radiobiology; 3D-ID; patient-specific dosimetry; treatment planning The tools and methodologies for performing radionuclide dosimetry for therapeutic nuclear medicine applications have evolved over the past 2 decades such that current research focuses on patient-specific 3-dimensional (3D) image or voxel-based approaches (1,2). In this work, we describe an extension of this methodology that incorporates radiobiologic modeling to account for the spatial distribution of absorbed dose and the effect of dose rate on biologic response. The methodology is incorporated into a software package, called 3D-RD, for 3D radiobiologic dosimetry.Patient-specific 3D imaging-based internal dosimetry is a methodology in which the patient's own anatomy and spatial distribution of radioactivity over time are factored into an absorbed dose calculation that provides as o...

A review of 3D image-based dosimetry, technical considerations and emerging perspectives in 90Y microsphere therapy

“…They showed good 89 Zr imaging characteristics in phantoms and a lower cost associated with production [129]. Given the comparable half-life of 89 Zr to 90 Y, the group then produced 18 F-based RMS [130]. They achieved a labeling efficiency of 95% and an in vitro stability study of >99%, showing histological analysis of microsphere distribution in the rabbit liver agreed with PET findings to within 3%.…”

“…64 Cu was excluded due to leaching of Cu(II), and 86 Y as it emits photons detected in the PET imaging window. They showed good 89 Zr imaging characteristics in phantoms and a lower cost associated with production [129]. Given the comparable half-life of 89 Zr to 90 Y, the group then produced 18 F-based RMS [130].…”

“…Recent work has labeled RMS with 64 Cu, 86 Y and 89 Zr with efficiencies of >95% (although 80% for 89 Zr) [128]. 64 Cu was excluded due to leaching of Cu(II), and 86 Y as it emits photons detected in the PET imaging window.…”

“…The code has been renamed 3D-RD [89] and recent validations were performed against a voxel S-value MIRD technique in a voxelized liver phantom with less than a 1% difference in absorbed dose [90] and more recently to examine the effects of tissue density over 3 different radionuclide treatments (including 90 Y-RE) with differences of 0.8% in both D T and D NL [91]. …”

Hybrid PET/CT and SPECT/CT Imaging

“…SPECT/CT might be useful for performing valid and clinically applicable dosimetry, for improving treatment planning, and for ensuring safe and effective radionuclide therapy (Boucek & Turner 2005, Thierens et al, 2005, Prideaux et al, 2007.…”