The Chesapeake Bay Program Modeling System: Overview and Recommendations for Future Development.

The Chesapeake Bay is the largest, most productive, and most biologically diverse estuary in the continental United States providing crucial habitat and natural resources for culturally and economically important species. Pressures from human population growth and associated development and agricultural intensification have led to excessive nutrient and sediment inputs entering the Bay, negatively affecting the health of the Bay ecosystem and the economic services it provides. The Chesapeake Bay Program (CBP) is a unique program formally created in 1983 as a multi-stakeholder partnership to guide and foster restoration of the Chesapeake Bay and its watershed.

Convolution-based estimation of organ dose in tube current modulated CT.

Estimating organ dose for clinical patients requires accurate modeling of the patient anatomy and the dose field of the CT exam. The modeling of patient anatomy can be achieved using a library of representative computational phantoms (Samei et al 2014 Pediatr. Radiol.

Practical dose point-based methods to characterize dose distribution in a stationary elliptical body phantom for a cone-beam C-arm CT system.

Purpose: To propose new dose point measurement-based metrics to characterize the dose distributions and the mean dose from a single partial rotation of an automatic exposure control-enabled, C-arm-based, wide cone angle computed tomography system over a stationary, large, body-shaped phantom.

Methods: A small 0.6 cm(3) ion chamber (IC) was used to measure the radiation dose in an elliptical body-shaped phantom made of tissue-equivalent material.

Dose equations for shift-variant CT acquisition modes using variable pitch, tube current, and aperture, and the meaning of their associated CTDI(vol).

Purpose: With the increasing clinical use of shift-variant CT protocols involving tube current modulation (TCM), variable pitch or pitch modulation (PM), and variable aperture a(t), the interpretation of the scanner-reported CTDI(vol) is called into question. This was addressed for TCM in their previous paper published by Dixon and Boone [Med. Phys.

Stationary table CT dosimetry and anomalous scanner-reported values of CTDIvol.

Purpose: Anomalous, scanner-reported values of CTDIvol for stationary phantom/table protocols (having elevated values of CTDIvol over 300% higher than the actual dose to the phantom) have been observed; which are well-beyond the typical accuracy expected of CTDIvol as a phantom dose. Recognition of these outliers as "bad data" is important to users of CT dose index tracking systems (e.g.

Dose equations for tube current modulation in CT scanning and the interpretation of the associated CTDIvol.

Purpose: The scanner-reported CTDI(vol) for automatic tube current modulation (TCM) has a different physical meaning from the traditional CTDI(vol) at constant mA, resulting in the dichotomy "CTDI(vol) of the first and second kinds" for which a physical interpretation is sought in hopes of establishing some commonality between the two.

Methods: Rigorous equations are derived to describe the accumulated dose distributions for TCM. A comparison with formulae for scanner-reported CTDI(vol) clearly identifies the source of their differences.

Utilization strategies for cumulative dose estimates: a review and rational assessment.

Over the past several years, the cancer risks associated with radiation from diagnostic imaging have received increased attention in both the medical literature and the lay press. In the midst of this heightened scrutiny, there has been growing support for the idea of tracking cumulative dose estimates that longitudinally document the accumulated medical radiation exposure of each individual patient. The authors review the current consensus model of radiation-induced carcinogenesis and use this framework to provide a rational assessment of several potential cumulative dose estimate utilization strategies.

Analytical equations for CT dose profiles derived using a scatter kernel of Monte Carlo parentage with broad applicability to CT dosimetry problems.

Purpose: Knowledge of the complete axial dose profile f(z), including its long scatter tails, provides the most complete (and flexible) description of the accumulated dose in CT scanning. The CTDI paradigm (including CTDIvol) requires shift-invariance along z (identical dose profiles spaced Sat equal intervals), and is therefore inapplicable to many of the new and complex shift-variant scan protocols, e.g.

Cone beam CT dosimetry: a unified and self-consistent approach including all scan modalities--with or without phantom motion.

Purpose: This article describes a common methodology and measurement technique, encompassing both conventional (helical and axial) CT scanning using phantom translation and cone beam (or narrow fan beam) CT scans about a stationary phantom. Cone beam CT systems having beam widths along the z-axis wide enough to cover a significant anatomical length (50-160 mm) in a single axial rotation (e.g.

Radiology of urolithiasis: implications of radiation exposure and new imaging modalities.

Computed tomography (CT) scanning is now the standard imaging technique for detecting and characterizing urolithiasis. However, the potential effects of the radiation exposure from CT examinations have raised concern among some physicians. This article describes the radiation doses for various urolithiasis-imaging techniques and describes techniques to optimize and reduce radiation exposures to patients undergoing these examinations.

Experimental validation of a versatile system of CT dosimetry using a conventional ion chamber: beyond CTDI100.

This article is an experimental demonstration and authentication of a new method of computed tomography dosimetry [R. L. Dixon, Med.

The effect of skull volume and density on differentiating gray and white matter on routine computed tomography scans of the head.

Increased volume and density of the skull makes computed tomography differentiation of gray and white matter (GM and WM, respectively) more difficult. The purpose of this investigation was to study the effects of skull volume and bone density on GM and WM differentiation. A total of 21 patients with thick skulls and 22 controls were included in this study.

An improved analytical model for CT dose simulation with a new look at the theory of CT dose.

Gagne [Med. Phys. 16, 29-37 (1989)] has previously described a model for predicting the sensitivity and dose profiles in the slice-width (z) direction for CT scanners.

Radiation protection standards: their evolution from science to philosophy.

The concept of applying constraints on individual sources to a small fraction of the public dose limit has been deemed inappropriate when shielding the medical X-ray sources. This represents a broad-based consensus of medical physics and radiological societies in the United States, and the report series on the shielding design for medical X-ray sources (including dental, X-ray imaging and therapeutic X ray) from the National Council on Radiation Protection and Measurements (NCRP) utilises 1 mSv y(-1) as a source control limit. In the present study, the rationale for such a conclusion is discussed, and a somewhat critical look at the current model of radiation protection of the public is made.

A new look at CT dose measurement: beyond CTDI.

Equations are derived for generating accumulated dose distributions and the dose line integral in a cylindrical dosimetry phantom for a helical CT scan series from the single slice dose profiles using convolution methods. This exposition will better clarify the nature of the dose distribution in helical CT, as well as providing the medical physicist with a better understanding of the physics involved in dose delivery and the measurement process. Also addressed is the concern that as radiation beam widths for multi-slice scanners get wider, the current methodology based on the measurement of the integral of the single slice profile using a 10 cm long ion chamber (CTDI100) may no longer be adequate.

CT diagnosis of acute flank pain from urolithiasis.

The use of noncontrast helical CT (NHCT) to assess patients with acute flank pain and hematuria for potential urinary tract stone disease was first reported in 1995. After several years of experience with the technique, sensitivity and specificity of NHCT has proven to be better than intravenous urography for evaluating ureteral stones. NHCT imaging findings for urinary calculi and the differential diagnosis are discussed in this article.

Secondary shielding barriers for diagnostic x-ray facilities: scatter and leakage revisited.

Methods are presented for determining the thickness requirements for barriers against scatter and leakage radiation generated in a diagnostic x-ray facility. Equations are developed that express the shielded doses due to scatter and leakage with explicit dependence on the operating potential used in clinical settings. The 1972 scatter experiment of Trout and Kelley is revisited, with suggested values for the scatter fraction that are somewhat different from those used in Report Number 49 of the NCRP.

Primary shielding barriers for diagnostic x-ray facilities: a new model.

Traditional methods of diagnostic x-ray shielding design assume that the raw primary beam impinges directly on the structural barrier with attenuation by the patient and by the hardware in the x-ray beam (cassette, cassette holder, x-ray table) being ignored. Moreover, primary barrier calculations are done assuming a single, conservatively high value of the operating potential, rather than the lower kVp values more representative of clinical usage. This results in extreme conservatism, which is no longer defensible in light of the lowered dose limit to a member of the general public of 1 mSv y-1, which is equal in magnitude to natural background radiation (excluding radon).

On the primary barrier in diagnostic x-ray shielding.

The traditional approach to shielding design for diagnostic x-ray facilities has been to designate as primary barriers the floor and those walls on which the useful beam may impinge, and to ignore the attenuation provided by the patient, grid, cassette, cassette holder, and x-ray table in computing the required thickness of these barriers. The degree of attenuation provided by the aforementioned materials has been measured on three-phase x-ray equipment including a variety of modern x-ray tables, grids, and cassettes. The primary beam is shown to be attenuated by more than two orders of magnitude at 100 kVp by the x-ray tables tested prior to impinging on the floor (ignoring patient attenuation).