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Internal photon and electron dosimetry of the newborn patient--a hybrid computational phantom study
Michael Wayson1, Choonsik Lee, George Sgouros
1J. Crayton Pruitt Family Department of Biomedical Engineering, University of Florida, Gainesville, FL 32611, USA. mikew13@ufl.edu
Insights
Accurate radiation dose estimates are crucial for pediatric nuclear medicine. This study presents a new computational phantom for newborn dosimetry, improving accuracy over existing models for better patient safety and optimized imaging.
Area of Science:
- Medical Physics
- Nuclear Medicine Dosimetry
- Pediatric Radiation Safety
Background:
- Accurate radiation absorbed dose estimation is essential for optimizing administered activity and assessing stochastic risk in nuclear medicine patients.
- Pediatric patients, especially newborns, require precise dosimetry due to heightened radiosensitivity and longer life expectancies.
- Existing methods using stylized phantoms may lack the necessary anatomical detail for accurate dose calculations in newborns.
Purpose of the Study:
- To develop a comprehensive model for electron and photon internal dosimetry in the reference newborn child.
- To calculate radionuclide S values using a high-resolution hybrid-voxel phantom for improved dose and risk evaluation.
- To compare newly derived S values with those from the OLINDA/EXM software and highlight discrepancies.
Main Methods:
- Utilized a high-resolution hybrid-voxel phantom of the reference newborn child from the University of Florida (UF) patient model series.
- Employed the MCNPX v2.6 radiation transport code to compute photon specific absorbed fractions (SAFs).
- Calculated electron SAFs by separately computing collisional and radiative components of organ dose for unique efficiency.
Main Results:
- Generated photon and electron SAFs for reference male and female newborns.
- Assembled a comprehensive set of S values for 16 common radionuclides used in newborn molecular imaging.
- Observed significant discrepancies (organ self-dose ratios 0.46-1.42, cross-dose ratios 0.04-3.49) compared to OLINDA/EXM, attributed to simplistic organ modeling in the latter.
Conclusions:
- Presented a comprehensive internal dosimetry model for newborn nuclear medicine patients based on the UF hybrid computational phantom.
- Provided photon dose response functions, photon and electron SAFs, and radionuclide S values for newborn dosimetry.
- These data are crucial for optimizing image quality and assessing stochastic risk in this vulnerable pediatric population.
Abstract:
Estimates of radiation absorbed dose to organs of the nuclear medicine patient are a requirement for administered activity optimization and for stochastic risk assessment. Pediatric patients, and in particular the newborn child, represent that portion of the patient population where such optimization studies are most crucial owing to the enhanced tissue radiosensitivities and longer life expectancies of this patient subpopulation. In cases where whole-body CT imaging is not available, phantom-based calculations of radionuclide S values--absorbed dose to a target tissue per nuclear transformation in a source tissue--are required for dose and risk evaluation. In this study, a comprehensive model of electron and photon dosimetry of the reference newborn child is presented based on a high-resolution hybrid-voxel phantom from the University of Florida (UF) patient model series. Values of photon specific absorbed fraction (SAF) were assembled for both the reference male and female newborn using the radiation transport code MCNPX v2.6. Values of electron SAF were assembled in a unique and time-efficient manner whereby the collisional and radiative components of organ dose--for both self- and cross-dose terms--were computed separately. Dose to the newborn skeletal tissues were assessed via fluence-to-dose response functions reported for the first time in this study. Values of photon and electron SAFs were used to assemble a complete set of S values for some 16 radionuclides commonly associated with molecular imaging of the newborn. These values were then compared to those available in the OLINDA/EXM software. S value ratios for organ self-dose ranged from 0.46 to 1.42, while similar ratios for organ cross-dose varied from a low of 0.04 to a high of 3.49. These large discrepancies are due in large part to the simplistic organ modeling in the stylized newborn model used in the OLINDA/EXM software. A comprehensive model of internal dosimetry is presented in this study for the newborn nuclear medicine patient based upon the UF hybrid computational phantom. Photon dose response functions, photon and electron SAFs, and tables of radionuclide S values for the newborn child--both male and female--are given in a series of four electronic annexes available at stacks.iop.org/pmb/57/1433/mmedia. These values can be applied to optimization studies of image quality and stochastic risk for this most vulnerable class of pediatric patients.
