The postnatal growth of ICRP target organs in reference humans: spleen and liver

Attempts to improve radiation dose estimates to infants and children are hampered because of the lack of mathematical models that describe the age variation in anatomical and physiological parameters. Specifically, for one anatomical parameter, organ size, there are no growth models available to the health physics community. In this paper, an empirical mathematical model is introduced for estimating age-specific masses of two ICRP target organs: the spleen and liver. That model, the Power Logistic Additive (PLA) growth model, is fitted to ICRP 23 organ growth data to determine five growth parameters. This model assumes that organs grow under the influence of two main processes: a primary (power function) and a sexual maturation (logistic function) process, which are additive from birth to adulthood. The results show that the model describes the ICRP growth data quite well. Growth parameters and tables listing the predicted masses and mass velocities as a function of age for each organ are provided for application in the ICRP modeling system.