title: Microdosimetric and Biological Effects of Photon Irradiation at Different Energies in Bone Marrow.
abstract: To ensure reliability and reproducibility of radiobiological data, it is necessary to standardize dosimetry practices across all research institutions. The photoelectric effect predominates over other interactions at low energy and in high atomic number materials such as bone, which can lead to increased dose deposition in soft tissue adjacent to mineral bone due to secondary radiation particles. This may produce radiation effects that deviate from higher energy photon irradiation that best model exposure from clinical radiotherapy or nuclear incidences. Past theoretical considerations have indicated that this process should affect radiation exposure of neighboring bone marrow (BM) and account for reported differences in relative biological effectiveness (RBE) for hematopoietic failure in rodents. The studies described herein definitively estimate spatial dose distribution and biological effectiveness within the BM compartment for (137)Cs gamma rays and 320 kVp X rays at two levels of filtration: 1 and 4 mm Cu half-value layer (HVL). In these studies, we performed: 1. Monte Carlo simulations on a 5 μm resolution model of mouse vertebrae and femur derived from micro-CT images; 2. In vitro biological experiments irradiating BM cells plated directly on the surface of a bone-equivalent material (BEM); and 3. An in vivo study on BM cell survival in irradiated live mice. Simulation results showed that the relative dose increased in proximity to bone at the lower radiation energies and produced averaged values of relative dose over the entire BM volume within imaged trabecular bone of 1.17, 1.08 and 1.01 for beam qualities of 1 mm Cu HVL, 4 mm Cu HVL and (137)Cs, respectively. In accordance with Monte Carlo simulations, in vitro irradiation of BM cells located on BEM and in vivo whole-body irradiation at a prescribed dose to soft tissue of 6 Gy produced relative cell killing of hematopoietic progenitors (CFU-C) that significantly increased for the 1 mm Cu HVL X rays compared to radiation exposures of higher photon energies. Thus, we propose that X rays of the highest possible kVp and filtration be used to investigate radiation effects on the hematopoietic system, as this will allow for better comparisons with high-energy photon exposures applied in radiotherapy or as anticipated in a nuclear event.
authors.affiliation: a  Medical Physics Graduate Program, Duke University, Durham, North Carolina;|b  Duke Radiation Dosimetry Laboratory and.
authors.forename: Matthew D
authors.initials: MD
authors.lastname: Belley
authors.affiliation: c  Department of Radiation Oncology, Duke University Medical Center, Durham, North Carolina;
authors.forename: Kathleen A
authors.initials: KA
authors.lastname: Ashcraft
authors.affiliation: c  Department of Radiation Oncology, Duke University Medical Center, Durham, North Carolina;
authors.forename: Chen-Ting
authors.initials: CT
authors.lastname: Lee
authors.affiliation: d  David H. Koch Institute for Integrative Cancer Research and.
authors.forename: Milton R
authors.initials: MR
authors.lastname: Cornwall-Brady
authors.affiliation: e  Institute for Medical Engineering and Science, Massachusetts Institute of Technology, Cambridge, Massachusetts;
authors.forename: Jane-Jane
authors.initials: JJ
authors.lastname: Chen
authors.affiliation: b  Duke Radiation Dosimetry Laboratory and.
authors.forename: Rathnayaka
authors.initials: R
authors.lastname: Gunasingha
authors.affiliation: f  SCANCO Medical AG, Bruettisellen, Switzerland; and.
authors.forename: Markus
authors.initials: M
authors.lastname: Burkhart
authors.affiliation: c  Department of Radiation Oncology, Duke University Medical Center, Durham, North Carolina;
authors.forename: Mark
authors.initials: M
authors.lastname: Dewhirst
authors.affiliation: b  Duke Radiation Dosimetry Laboratory and.|c  Department of Radiation Oncology, Duke University Medical Center, Durham, North Carolina;|g  Department of Radiology, Duke University Medical Center, Durham, North Carolina.
authors.forename: Terry T
authors.initials: TT
authors.lastname: Yoshizumi
authors.affiliation: e  Institute for Medical Engineering and Science, Massachusetts Institute of Technology, Cambridge, Massachusetts;
authors.forename: Julian D
authors.initials: JD
authors.lastname: Down
mesh_terms: D000818:Animals; D001853:Bone Marrow / Q000528:radiation effects*; D016923:Cell Death / Q000528:radiation effects; D006412:Hematopoietic Stem Cells / Q000528:radiation effects; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D017785:Photons; D011829:Radiation Dosage; D014965:X-Rays