Room: AAPM ePoster Library
Purpose: Reliable estimates of radiation dose to bone marrow are critical to understanding the risk of radiation-induced cancers from medical, occupational, and space-related exposures. Traditional methods of estimating bone marrow dose in Monte Carlo simulations include indirect estimates based on dose to surrogate volumes or average dose to soft tissue, and often poorly represent the actual bone marrow.
Methods: This paper describes and evaluates a method for estimating dose to bone marrow volumes using an improved fidelity version of the MIRD (medical internal radiation dose) organ-based human phantom. Physical bone marrow volumes were carved into each bone of the human phantom in the Monte Carlo geometry in GEANT4, based on known bone marrow characteristics and distribution in the 40-year-old adult. The MIRD phantom then underwent simulated irradiation in relevant example scenarios representing medical, occupational, and space-related exposures. Total dose equivalent to the bone marrow was calculated for each scenario using the improved fidelity MIRD model and compared to results using three traditional indirect estimation
methods: proportion of dose to bone, proportion of dose to homogeneous bone/marrow, and average soft tissue dose.
Results: Results show that in the medical example, at clinical X-ray energies, the bone marrow dose equivalent may be overestimated by up to a factor of three when using the traditional methods versus using the improved fidelity MIRD method. In the occupational and space radiation examples, at gamma and galactic cosmic ray energies, results showed no significant difference in bone marrow dose equivalent based on which of the four calculation methods was used.
Conclusion: Medical physicists should use the results of this study to understand the impact of how the selected method of bone marrow dose calculation affects the dose estimate.
Funding Support, Disclosures, and Conflict of Interest: This work was partially funded by the presenting author's graduate fellowship provided by The Aerospace Corporation, El Segundo, California.
Not Applicable / None Entered.