Estimating the CTDI with helical acquisitions: Results from a national generalizability study.

Background: While many clinical computed tomography (CT) protocols use helical scanning, the traditional method for measuring the volume CT Dose Index (CTDI) requires modifying the helical protocol to perform a single axial rotation. This modification can present challenges and mismatched settings across various scanner models.

Purpose: This study investigates the generalizability of a helical methodology for estimating CTDI across a diverse range of participants, CT scanner models, and protocol parameters.

Specific absorbed fractions for a revised series of the UF/NCI pediatric reference phantoms: internal photon sources.

Assessment of radiation absorbed dose to internal organs of the body from the intake of radionuclides, or in the medical setting through the injection of radiopharmaceuticals, is generally performed based upon reference biokinetic models or patient imaging data, respectively. Biokinetic models estimate the time course of activity localized to source organs. The time-integration of these organ activity profiles are then scaled by the radionuclide S-value, which defines the absorbed dose to a target tissue per nuclear transformation in various source tissues.

Specific absorbed fractions for a revised series of the UF/NCI pediatric reference phantoms: internal electron sources.

In both the International Commission on Radiological Protection (ICRP) and Medical Internal Radiation Dose (MIRD) schemata of internal dosimetry, the S-value is defined as the absorbed dose to a target organ per nuclear decay of the radionuclide in a source organ. Its computation requires data on the energies and yields of all radiation emissions from radionuclide decay, the mass of the target organ, and the value of the absorbed fraction-the fraction of particle energy emitted in the source organ that is deposited in the target organ. The specific absorbed fraction (SAF) is given as the ratio of the absorbed fraction and the target mass.

The helically-acquired CTDI as an alternative to traditional methodology.

Purpose: Most clinical computed tomography (CT) protocols use helical scanning; however, the traditional method for CTDI measurement replaces the helical protocol with an axial scan, which is not easily accomplished on many scanners and may lead to unmatched collimation settings and bowtie filters. This study assesses whether CTDI can be accurately measured with a helical scan and determines the impact of pitch, collimation width, and excess scan length.

Methods: CTDI was measured for 95 helical protocols on 31 CT scanners from all major manufacturers.

Titration of Folate Pathway Enzymes.

How enzymes behave in cells is likely different from how they behave in the test tube. Previous studies find that osmolytes interact weakly with folate. Removal of the osmolyte from the solvation shell of folate is more difficult than removal of water, which weakens binding of folate to its enzyme partners.

Suggested reference values for regional blood volumes in children and adolescents.

Estimates of regional blood volumes (BVs) in humans are needed in dosimetric models of radionuclides and radiopharmaceuticals that decay in the circulation to a significant extent. These values are also needed to refine models of tissue elemental composition in computational human phantoms of both patients and exposed members of the general public. The International Commission on Radiological Protection (ICRP) in its Publication 89 provides reference values for total blood content in the full series of their reference individuals, to include the male and female newborn, 1 year-old, 5 year-old, 10 year-old, 15 year-old, and adult.

Comparative Dosimetry for Ga-DOTATATE: Impact of Using Updated ICRP Phantoms, S Values, and Tissue-Weighting Factors.

The data that have been used in almost all calculations of MIRD S value absorbed dose and effective dose are based on stylized anatomic computational phantoms and tissue-weighting factors adopted by the International Commission on Radiological Protection (ICRP) in its publication 60. The more anatomically realistic phantoms that have recently become available are likely to provide more accurate effective doses for diagnostic agents. Ga-DOTATATE is a radiolabeled somatostatin analog that binds with high affinity to somatostatin receptors, which are overexpressed in neuroendocrine tumors and can be used for diagnostic PET/CT-based imaging.

Depth-dependent concentrations of hematopoietic stem cells in the adult skeleton: Implications for active marrow dosimetry.

Purpose: The hematopoietically active (or red) bone marrow is the target tissue assigned in skeletal dosimetry models for assessment of stochastic effects (leukemia induction) as well as tissue reactions (marrow toxicity). Active marrow, however, is in reality a surrogate tissue region for specific cell populations, namely the hematopoietic stem and progenitor cells. Present models of active marrow dosimetry implicitly assume that these cells are uniformly localized throughout the marrow spaces of trabecular spongiosa.

Quantitative impact of changes in marrow cellularity, skeletal size, and bone mineral density on active marrow dosimetry based upon a reference model.

Purpose: The hematopoietically active tissues of skeletal bone marrow are a prime target for computational dosimetry given potential risks of leukemia and, at higher dose levels, acute marrow toxicity. The complex three-dimensional geometry of trabecular spongiosa, however, complicates schema for dose assessment in such a way that only a few reference skeletal models have been developed to date, and which are based upon microimaging of a limited number of cadaveric bone spongiosa cores. The question then arises as to what degree of accuracy is achievable from reference skeletal dose models when applied to individual patients or specific exposed populations?

Methods: Patient variability in marrow dosimetry were quantified for three skeletal sites - the ribs, lumbar vertebrae, and cranium - for the beta-emitters Ca, Sm, and Y, and the alpha-particle emitters Ra, Rn, and Po, the latter two being the immediate progeny of the former.