These results further validate the usefulness of nuclear magnetic resonance oximetry as a predictor of response to radiation therapy.

The simultaneous measurement of three oxygen-sensitive parameters [arterial hemoglobin oxygen saturation (SaO2), tumor vascular-oxygenated hemoglobin concentration ([HbO2]), and tumor oxygen tension (pO2)] in response to hyperoxic respiratory challenge is demonstrated in rat breast tumors. The effects of two hyperoxic gases [oxygen and carbogen (5% CO2 and 95% O2)] were compared, by use of two groups of Fisher rats with subcutaneous 13762NF breast tumors implanted in pedicles on the foreback. Two different gas-inhalation sequences were compared, i.e., air-carbogen-air-oxygen-air and air-oxygen-air-carbogen-air. The results demonstrate that both of the inhaled, hyperoxic gases significantly improved the tumor oxygen status. All three parameters displayed similar dynamic response to hyperoxic gas interventions, but with different response times: the fastest for arterial SaO2, followed by biphasic changes in tumor vascular [HbO2], and then delayed responses for pO2. Both of the gases induced similar changes in vascular oxygenation and regional tissue pO2 in the rat tumors, and changes in [HbO2] and mean pO2 showed a linear correlation with large standard deviations, which presumably results from global versus local measurements. Indeed, the pO2 data revealed hetergeneous regional response to hyperoxic interventions. Although preliminary near-infrared measurements had been demonstrated previously in this model, the addition of the pO2 optical fiber probes provides a link between the noninvasive relative measurements of vascular phenomena based on endogenous reporter molecules, with the quantitative, albeit, invasive pO2 determinations.

Hybrid phantoms represent a third generation of computational models of human anatomy needed for dose assessment in both external and internal radiation exposures. Recently, we presented the first whole-body hybrid phantom of the ICRP reference newborn with a skeleton constructed from both non-uniform rational B-spline and polygon-mesh surfaces (Lee et al 2007 Phys. Med. Biol. 52 3309-33). The skeleton in that model included regions of cartilage and fibrous connective tissue, with the remainder given as a homogenous mixture of cortical and trabecular bone, active marrow and miscellaneous skeletal tissues. In the present study, we present a comprehensive skeletal tissue model of the ICRP reference newborn to permit a heterogeneous representation of the skeleton in that hybrid phantom set-both male and female-that explicitly includes a delineation of cortical bone so that marrow shielding effects are correctly modeled for low-energy photons incident upon the newborn skeleton. Data sources for the tissue model were threefold. First, skeletal site-dependent volumes of homogeneous bone were obtained from whole-cadaver CT image analyses. Second, selected newborn bone specimens were acquired at autopsy and subjected to micro-CT image analysis to derive model parameters of the marrow cavity and bone trabecular 3D microarchitecture. Third, data given in ICRP Publications 70 and 89 were selected to match reference values on total skeletal tissue mass. Active marrow distributions were found to be in reasonable agreement with those given previously by the ICRP. However, significant differences were seen in total skeletal and site-specific masses of trabecular and cortical bone between the current and ICRP newborn skeletal tissue models. The latter utilizes an age-independent ratio of 80%/20% cortical and trabecular bone for the reference newborn. In the current study, a ratio closer to 40%/60% is used based upon newborn CT and micro-CT skeletal image analyses. These changes in mineral bone composition may have significant dosimetric implications when considering localized marrow dosimetry for radionuclides that target mineral bone in the newborn child.

This report evaluates the spatial profile of blood vessel fragments (BVFs) and CD34 ؉ and CD117 ؉ hematopoietic stem and progenitor cells (HSPCs) in human cancellous bone. Bone specimens were sectioned, immunostained (anti-CD34 and anti-CD117), and digitally imaged. Immunoreactive cells and vessels were then optically and morphometrically identified and labeled on the corresponding digital image. IntroductionQuantifying the spatial profile of blood vessels and primitive cell populations most susceptible to myelosuppression or hematologic toxicity is of major interest in basic cancer research, bone marrow transplantation, and molecular radiotherapy. [1][2][3] Although several groups have investigated the spatial location of hematopoietic stem and progenitor cells (HSPCs) in murine models, 4-7 evidence for corresponding HSPC spatial profiles within human bone marrow has only recently been established. 8 In their study, Watchman et al used novel methods for the digital quantification of the CD34 ϩ hematopoietic stem cells and blood vessel fragments (BVFs) in human iliac crest. 8 The present study uses similar techniques of immunohistochemistry and digital image processing to directly measure the concentration of BVFs and CD34 ϩ HSPCs as a function of distance from the most proximal trabecular surface in human bone marrow. The study further advances the findings of Watchman et al, however, through (1) immunohistochemical stratification of the additional population of CD117 ϩ hematopoietic stem and progenitor cells, (2) consideration of a possible bone-site dependence of the BVF and HSPC spatial gradient, (3) use of larger field-of-view marrow specimens through autopsy harvest, and (4) explicit consideration of active versus total bone marrow area. MethodsPostmortem bone samples were collected during the autopsy of 9 recently deceased patients determined to be absent of marrow disease under a Health Insurance Portability and Accountability Act-compliant and University of Florida institutional review board-approved protocol that followed the Declaration of Helsinki provisions. Sections of bone were collected from the right iliac crest, L 1 vertebrae, and 1 left rib, within 24 hours of death. Excised bone samples were placed in stock formaldehyde, rough sectioned, decalcified, and acid neutralized following the manufacturer's instructions (Formical-4 and Cal-Arrest; Decal Chemical Corp). The paraffin tissue blocks were faced and 4 sequential sections were collected from each specimen at a thickness of 5 m. ImmunohistochemistrySerial sections collected from decalcified, paraffin-embedded blocks were manually immunostained using mouse anti-CD34 (dilution 1:25, QBEND10; DAKO Cytomation) and rabbit anti-CD117 (dilution 1:300, c-Kit; DAKO Cytomation). Antigen retrieval was achieved using heat-induced epitope retrieval and treatment of slides with 10 mM Citra buffer (pH 6.0), after which slides were stained by the ABC-Elite method (Vector Labs) following the manufacturer's instructions. Positive signal was detected with dia...

Current bone marrow dosimetry methods inherently assume that the target cells of interest for the assessment of leukemia risk (stochastic effects) or marrow toxicity (deterministic effects) are uniformly localized throughout the marrow cavities of cancellous bone. Previous studies on mouse femur, however, have demonstrated a spatial gradient for the hematopoietic stem and progenitor cells, with higher concentrations near the bone surfaces. The objective of the present study was to directly measure the spatial concentration of these cells, as well as marrow vasculature structures, within images of human disease-free bone marrow. Methods: Core-biopsy samples of normal bone marrow from the iliac crest were obtained from clinical cases at Shands Hospital at the University of Florida Department of Pathology. The specimens were sectioned and immunohistochemically stained for CD34 (red) and CD31 (brown) antigens. These 2 stains were used simultaneously to differentiate between hematopoietic stem and progenitor cells (CD34 1 /CD31 2 ) and vascular endothelium (CD34 1 /CD31 1 ). Distances from hematopoietic CD34 1 cells and blood vessels to the nearest bone trabecula surface were measured digitally and then binned in 50-mm increments, with the results then normalized per unit area of marrow tissue. The distances separating hematopoietic CD34 1 cells from vessels were also tallied. Results: Hematopoietic CD34 1 cells were found to exist along a linear spatial gradient with a maximal areal concentration localized within the first 50 mm of the bone surfaces. An exponential spatial concentration gradient was found in the concentration of blood vessel fragments within the images. Distances between hematopoietic CD34 1 cells and blood vessels exhibited a lognormal distribution indicating a shared spatial niche. Conclusion: Study results confirm that the spatial gradient of hematopoietic stem and progenitor cells previously measured in mouse femur is also present within human cancellous bone. The dosimetric implication of these results may be significant for those scenarios in which the absorbed dose itself is nonuniformly delivered across the marrow tissues, as would be the case for a low-energy b-or a-particle emitter localized on the bone surfaces.