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Dosimetric considerations of 99m Tc-MDP uptake within the epiphyseal plates of the long bones of pediatric patients.
- Source :
-
Physics in medicine and biology [Phys Med Biol] 2020 Dec 02; Vol. 65 (23), pp. 235025. Date of Electronic Publication: 2020 Dec 02. - Publication Year :
- 2020
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Abstract
- Skeletal scintigraphy is most performed in pediatric patients using the radiopharmaceutical <superscript>99m</superscript> Tc labelled methylene diphosphonate ( <superscript>99m</superscript> Tc-MDP). Reference biokinetic models for <superscript>99m</superscript> Tc-MDP indicate 50% of the administered activity is uniformly localized to the interior bone surfaces (trabecular and cortical regions), yet imaging data clearly show some preferential uptake to the epiphyseal growth plates of the long bones. To explore the dosimetric consequences of these regional activity concentrations, we have modified mesh-type computational phantoms of the International Commission on Radiological Protection (ICRP) reference pediatric series to explicitly include geometric models of the epiphyseal growth plates (2 mm in thickness) within the left/right, distal/proximal ends of the humeri, radii, ulnae, femora, tibia, and fibulae. Bone mineral activity from the ICRP Publication 128 biokinetic model for <superscript>99m</superscript> Tc-MDP (ICRP 2015) was then partitioned to the growth plates at values of 0.5%, 4.4%, 8.3%, 12.2%, 16.1%, and 20%. Radiation transport simulations were performed to compute <superscript>99m</superscript> Tc S-values and organ dose coefficients to the soft tissues and to bone site-specific regions of spongiosa. As the percentage of bone activity assigned to the growth plates was increased (from 0.5% to 20%), absorbed doses to the soft tissue organs, active bone marrow, bone endosteum (BE), as well as the detriment-weighted dose, were shown to decrease from their nominal values (no substantial growth plate activity), while epiphyseal plate self-doses increased. In the 15 year old male phantom, moving from 0.5% to 20% relative bone activity within the epiphyseal plates resulted in a 15% reduction in active marrow (AM) and BE dose, a 10% reduction in mean soft tissue and detriment-weighted dose, and a 6.3-fold increase in epiphyseal plate self-dose. In the newborn female phantom, we observed a 18% decrease in AM and BE dose, a 10% decrease in mean soft tissue dose, a 15% decrease in detriment-weighted dose, and 12.8-fold increase in epiphyseal plate self-dose. Increases (to 3 mm) and decreases (to 1 mm) in the assumed growth plate thickness of our models were shown to impact only the growth plate self-dose. Future work in differential quantification of <superscript>99m</superscript> Tc-MDP activity-growth plates versus other bone surfaces-is required to provide clinically realistic data on activity partitioning as a function of patient age, and perhaps skeletal site. The phantom series presented here may be used to develop more optimized age-related guidance on <superscript>99m</superscript> Tc-MDP administered activities to children.
- Subjects :
- Adolescent
Biological Transport
Bone and Bones metabolism
Child
Child, Preschool
Female
Growth Plate diagnostic imaging
Humans
Infant, Newborn
Male
Radiometry
Radionuclide Imaging
Tomography, X-Ray Computed
Bone and Bones diagnostic imaging
Growth Plate metabolism
Technetium Tc 99m Medronate metabolism
Subjects
Details
- Language :
- English
- ISSN :
- 1361-6560
- Volume :
- 65
- Issue :
- 23
- Database :
- MEDLINE
- Journal :
- Physics in medicine and biology
- Publication Type :
- Academic Journal
- Accession number :
- 33263312
- Full Text :
- https://doi.org/10.1088/1361-6560/abb1db