Nuclear medicine dosimetry of cranial substructures using novel Korean pediatric and adult computational head phantoms

Objectives Clinical neuroimaging applications of single photon emission computed tomography (SPECT) and positron emission tomography (PET) is becoming more prevalent. Calculating absorbed dose to cranial substructures from intracranial radionuclide distributions with physical measurements is impractical, but computational dose estimates are a feasible alternative. In the current study, we developed a series of Korean pediatric and adult computational head models and applied them to calculating dose to cranial substructures of various sized patients.

Methods A template cranial model containing contoured substructures was created from an existing 7 years old Korean voxel phantom [1]. Age-specific head phantoms were generated by scaling the template head phantom using measurements from the Korean National Survey of Body Size and a non-uniform morphing technique. Voxelized head phantoms were imported into the Monte Carlo transport code MCNPX 2.7 and age-dependent specific absorbed fraction (SAF) values were calculated using single energy photons ranging from 0.01-4MeV sourced from 20 different tissues modeled in the head phantoms.

Results Head phantoms based on the Korean population were created for five age groups. SAF values for 20 source and 20 target organ combinations were calculated for the five head phantoms. Compared to the oldest head phantom (20-24 year old), the youngest phantom (6 year old) received up to 1.4 times greater self-SAF (e.g., cerebellum) and up to 1.8 times greater cross-fire SAF (e.g., cerebellum < eye balls).

Conclusions A variety of age-specific Korean head phantoms containing cranial substructures have been created. These phantoms were utilized in a Monte Carlo program to calculate SAF values for intracranial radiation sources. Using this SAF data, absorbed dose to various cranial substructures can be calculated for a patient undergoing a cranial neuroimaging procedure.

Research Support This research was funded by the MSIP (Ministry of Science, ICT & Future Planning), Korea in the ICT R&D Program 2013, and by the intramural research program of the National Institutes of Health, National Cancer Institute, Division of Cancer Epidemiology and Genetics.