Five pediatric head and brain mathematical models for use in internal dosimetry

Area of Science:

• Medical Physics
• Radiological Sciences
• Pediatric Dosimetry

Background:

• Current pediatric neuroimaging dosimetry models lack the anatomical detail for precise suborgan brain dosimetry.
• The Medical Internal Radiation Dose (MIRD) Committee adopted a detailed adult head and brain model, necessitating pediatric adaptations.

Purpose of the Study:

• To develop detailed pediatric head and brain dosimetric models for internal dosimetry.
• To enable more accurate radiation dose calculations in pediatric nuclear medicine brain procedures.

Main Methods:

• Developed five new head and brain models for ages newborn, 1, 5, 10, and 15 years, based on the MIRD adult model.
• Utilized the Monte Carlo transport code EGS4 to calculate absorbed energy fractions for monoenergetic photons and electrons (10 keV-4 MeV).
• Generated S values for various ages using radionuclide decay data, considering 12 source and 15 target regions for 99mTc.

Main Results:

• Calculated absorbed fractions for monoenergetic photons and electrons across a wide energy range.
• Investigated explicit positron transport and annihilation photon contributions, finding no significant difference compared to traditional methods for S values.
• Observed a rapid decrease in self-absorbed fractions within brain subregions with increasing particle energy, highlighting the need for electron transport.

Conclusions:

• The developed series of five pediatric dosimetric head and brain models provides enhanced anatomical detail.
• These models facilitate more precise dosimetry of radiopharmaceuticals in pediatric nuclear medicine brain procedures.
• The findings underscore the importance of electron transport within pediatric brain subregions for accurate dosimetry.