HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Bouchet, L. G. Articles by Bolch, W. E. Search for Related Content PubMed PubMed Citation Articles by Bouchet, L. G. Articles by Bolch, W. E.

Five Pediatric Head and Brain Mathematical Models for Use in Internal Dosimetry

Department of Nuclear and Radiological Engineering, University of Florida, Gainesville, Florida

Correspondence: For correspondence or reprints contact: Wesley E. Bolch, PhD, Department of Nuclear and Radiological Engineering, University of Florida, Gainesville, FL 32611-8300.

ABSTRACT

Mathematical models of the head and brain currently used in pediatric neuroimaging dosimetry lack the anatomic detail needed to provide the necessary physical data for suborgan brain dosimetry. To overcome this limitation, the Medical Internal Radiation Dose (MIRD) Committee of the Society of Nuclear Medicine recently adopted a detailed dosimetric model of the head and brain for the adult. Methods: New head and brain models have been developed for a newborn, 1 , 5, 10 and 15 y old for use in internal dosimetry. These models are based on the MIRD adult head and brain model and on published head and brain dimensions. They contain the same eight brain subregions and the same head regions as the adult model. These new models were coupled with the Monte Carlo transport code EGS4, and absorbed fractions of energy were calculated for 14 sources of monoenergetic photons and electrons in the energy range of 10 keV–4 MeV. These absorbed fractions were then used along with radionuclide decay data to generate S values for all ages for ^99mTc, considering 12 source and 15 target regions. Results: Explicit transport of positrons was also considered with separation of the annihilation photons component to the absorbed fraction of energy in the calculation of S values for positron emitting radionuclides. No statistically significant differences were found when S values were calculated for positron-emitting radionuclides under explicit consideration of the annihilation event compared with the traditional assumption of a uniform distribution of 0.511-MeV photons. Conclusion: The need for electron transport within the suborgan brain regions of these pediatric phantoms was reflected by the relatively fast decrease of the self-absorbed fraction within many of the brain subregions, with increasing particle energy. This series of five dosimetric head and brain models will allow more precise dosimetry of radiopharmaceuticals in pediatric nuclear medicine brain procedures.

Key Words: brain dosimetry • suborgan dosimetry • pediatric dosimetry • MIRD schema • S values • ^99mTc