Comprehensive Image-Based Dosimetric Analysis of Alpha Particle Dose in Bone Marrow
J Pan*, C Watchman, University of Arizona, Tucson, AZWE-C-BRB-12 Wednesday 10:30:00 AM - 12:30:00 PM Room: Ballroom B
Purpose: In this study, a comprehensive analysis of alpha particle dose to bone marrow was developed. Using autopsy spongiosa samples and an in house Monte Carlo program, dosimetry data was calculated for macroscopic dosimetry (MIRD schema) to microdosimetric methods. This investigation provides a uniform comparison of these different methodologies.
Methods: Autopsy samples of spongiosa from two bone sites (iliac crest and vertebrae) were sectioned and immunohistochemically stained (anti-CD34) to identify hematopoietic stem and progenitor cells (HSPC). Digitized 2-dimensional image was segmented based on pixel intensity to differentiate between bone trabeculae, red bone marrow and adipocytes. Individual HSPC were also identified. The processed image was used as input for an alpha-particle Monte Carlo radiation transport program where dosimetric data was calculated for absorbed fractions, hit probabilities and z-values.
Results: Energies of 0.5-10 MeV were investigated. Source distributions (bone, fat, red bone marrow and bone surface) of alpha particles were obtained. Absorbed fraction of each tissue region and HSPC were obtained. Probability of receiving hit of alpha particles of HSPC and nucleus were also calculated. Data for each source and target combination indicated significant dose differences to the HSPC depending on the methodology used to calculate the final dose estimate.
Conclusions: Results of this study indicate the discrepancy between macroscopic and microscopic dose methods. While the microscopic methods provide a more detailed assessment of HSPC dosing they lack clinical utility. Additional work is required to bridge these two dosimetric spatial domains before bone marrow dose calculations may be clinically implemented.