Skeletal dosimetry in the MAX06 and the FAX06 phantoms for external exposure to photons based on vertebral 3D-microCT images

Abstract

3D-microCT images of vertebral bodies from three different individuals have been segmented into trabecular bone, bone marrow and bone surface cells (BSC), and then introduced into the spongiosa voxels of the MAX06 and the FAX06 phantoms, in order to calculate the equivalent dose to the red bone marrow (RBM) and the BSC in the marrow cavities of trabecular bone with the EGSnrc Monte Carlo code from whole-body exposure to external photon radiation. The MAX06 and the FAX06 phantoms consist of about 150 million 1.2 mm cubic voxels each, a part of which are spongiosa voxels surrounded by cortical bone. In order to use the segmented 3D-microCT images for skeletal dosimetry, spongiosa voxels in the MAX06 and the FAX06 phantom were replaced at runtime by so-called micro matrices representing segmented trabecular bone, marrow and BSC in 17.65, 30 and 60 microm cubic voxels. The 3D-microCT image-based RBM and BSC equivalent doses for external exposure to photons presented here for the first time for complete human skeletons are in agreement with the results calculated with the three correction factor method and the fluence-to-dose response functions for the same phantoms taking into account the conceptual differences between the different methods. Additionally the microCT image-based results have been compared with corresponding data from earlier studies for other human phantoms.

Radiation Dose From Kilovoltage Cone Beam Computed Tomography in an Image-Guided Radiotherapy Procedure

“…Recent studies (30)(31)(32) of the interactions of radiation with bone material reported that the dose to the marrow may be much greater than the dose to the soft tissues because of the close proximity of marrow to cortical bone. The volume and magnitude of additional dose from repeated imaging guidance procedures may increase the risk of bone marrow suppression already present in the clinical setting of combined radiotherapy and chemotherapy regimens (33) for patients of all ages.…”

NORMAN-05 conversion coefficients for monoenergetic neutrons below 20MeV

“…On the basis of what Kramer et al (2006) found for photons, probably the applied method could bring to an over-estimation of the conversion coefficients, but the ratios between the different models should be preserved.…”

“…Recent papers (Kramer et al, 2006(Kramer et al, , 2007 demonstrate that modeling the inner bone structure (cortical, spongiosa and bone surface cells) using microCT samples implies a lower estimate of the energy deposition in RBM and bone surface cells for external photon exposures. It should be of great interest to investigate the effect of a similar detailed bone structures modeling in the case of external neutron irradiation, that was not yet analyzed, but this is outside of the present work scope.…”

Diversification of Existing Reference Phantoms in Nuclear Medicine: Calculation of Specific Absorbed Fractions for 21 Mathematical Phantoms and Validation Through Dose Estimates Resulting from the Administration of 18F-FDG

“…The dose received by the red bone marrow by photon cross-irradiation was calculated by using the so-called three-factor method, which is described in detail in Zankl et al 27 and Kramer et al 28 . The skeleton of the mathematic phantoms in the present study is comprised of a homogeneous mixture of bone and marrow.…”