Efforts to assess in utero radiation doses and related quantities to the developing fetus should account for the presence of the surrounding maternal tissues. Maternal tissues can provide varying levels of protection to the fetus by shielding externally-emitted radiation or, alternatively, can become sources of internally-emitted radiation following the biokinetic uptake of medically-administered radiopharmaceuticals or radionuclides located in the surrounding environment--as in the case of the European Union's SOLO project (Epidemiological Studies of Exposed Southern Urals Populations). The University of Florida had previously addressed limitations in available computational phantom representation of the developing fetus by constructing a series of hybrid computational fetal phantoms at eight different ages and three weight percentiles. Using CT image sets of pregnant patients contoured using 3D-DOCTOR(TM), the eight 50th percentile fetal phantoms from that study were systematically combined in Rhinoceros(TM) with the UF adult non-pregnant female to yield a series of reference pregnant female phantoms at fetal ages 8, 10, 15, 20, 25, 30, 35 and 38 weeks post-conception. Deformable, non-uniform rational B-spline surfaces were utilized to alter contoured maternal anatomy in order to (1) accurately position and orient each fetus and surrounding maternal tissues and (2) match target masses of maternal soft tissue organs to reference data reported in the literature.
Purpose:
Coherent scatter based imaging has shown improved contrast and molecular specificity over conventional digital mammography however the biological risks have not been quantified due to a lack of accurate information on absorbed dose. This study intends to characterize the dose distribution and average glandular dose from coded aperture coherent scatter spectral imaging of the breast. The dose deposited in the breast from this new diagnostic imaging modality has not yet been quantitatively evaluated. Here, various digitized anthropomorphic phantoms are tested in a Monte Carlo simulation to evaluate the absorbed dose distribution and average glandular dose using clinically feasible scan protocols.
Methods:
Geant4 Monte Carlo radiation transport simulation software is used to replicate the coded aperture coherent scatter spectral imaging system. Energy sensitive, photon counting detectors are used to characterize the x‐ray beam spectra for various imaging protocols. This input spectra is cross‐validated with the results from XSPECT, a commercially available application that yields x‐ray tube specific spectra for the operating parameters employed. XSPECT is also used to determine the appropriate number of photons emitted per mAs of tube current at a given kVp tube potential. With the implementation of the XCAT digital anthropomorphic breast phantom library, a variety of breast sizes with differing anatomical structure are evaluated. Simulations were performed with and without compression of the breast for dose comparison.
Results:
Through the Monte Carlo evaluation of a diverse population of breast types imaged under real‐world scan conditions, a clinically relevant average glandular dose for this new imaging modality is extrapolated.
Conclusion:
With access to the physical coherent scatter imaging system used in the simulation, the results of this Monte Carlo study may be used to directly influence the future development of the modality to keep breast dose to a minimum while still maintaining clinically viable image quality.
<p>The supplementary file contains 3 supplemental figures. Supplementary Figure S1 shows the kinetics of Ki67 expression by CD4 and CD8 T cells following treatment with ipilimumab. Supplementary Figure S2 shows the change in TCR clonality over time following treatment with ipilimumab. Supplementary Figure S3 shows the changes in clonotype frequencies of sorted CD4+ and CD8+ T cells with ipilimumab.</p>
<p>The supplementary file contains 3 supplemental figures. Supplementary Figure S1 shows the kinetics of Ki67 expression by CD4 and CD8 T cells following treatment with ipilimumab. Supplementary Figure S2 shows the change in TCR clonality over time following treatment with ipilimumab. Supplementary Figure S3 shows the changes in clonotype frequencies of sorted CD4+ and CD8+ T cells with ipilimumab.</p>
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