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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. Since its inception, the CBP Partnership has been developing, updating, and applying a complex linked modeling system of watershed, airshed, and estuary models as a planning tool to inform strategic management decisions and Bay restoration efforts. This paper provides a description of the 2017 CBP Modeling System and the higher trophic level models developed by the NOAA Chesapeake Bay Office, along with specific recommendations that emerged from a 2018 workshop designed to inform future model development. Recommendations highlight the need for simulation of watershed inputs, conditions, processes, and practices at higher resolution to provide improved information to guide local nutrient and sediment management plans. More explicit and extensive modeling of connectivity between watershed landforms and estuary sub-areas, estuarine hydrodynamics, watershed and estuarine water quality, the estuarine-watershed socioecological system, and living resources will be important to broaden and improve characterization of responses to targeted nutrient and sediment load reductions. Finally, the value and importance of maintaining effective collaborations among jurisdictional managers, scientists, modelers, support staff, and stakeholder communities is emphasized. An open collaborative and transparent process has been a key element of successes to date and is vitally important as the CBP Partnership moves forward with modeling system improvements that help stakeholders evolve new knowledge, improve management strategies, and better communicate outcomes.

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. 44 460-7). The modeling of the dose field can be challenging for CT exams performed with a tube current modulation (TCM) technique. The purpose of this work was to effectively model the dose field for TCM exams using a convolution-based method. A framework was further proposed for prospective and retrospective organ dose estimation in clinical practice. The study included 60 adult patients (age range: 18-70 years, weight range: 60-180 kg). Patient-specific computational phantoms were generated based on patient CT image datasets. A previously validated Monte Carlo simulation program was used to model a clinical CT scanner (SOMATOM Definition Flash, Siemens Healthcare, Forchheim, Germany). A practical strategy was developed to achieve real-time organ dose estimation for a given clinical patient. CTDIvol-normalized organ dose coefficients ([Formula: see text]) under constant tube current were estimated and modeled as a function of patient size. Each clinical patient in the library was optimally matched to another computational phantom to obtain a representation of organ location/distribution. The patient organ distribution was convolved with a dose distribution profile to generate [Formula: see text] values that quantified the regional dose field for each organ. The organ dose was estimated by multiplying [Formula: see text] with the organ dose coefficients ([Formula: see text]). To validate the accuracy of this dose estimation technique, the organ dose of the original clinical patient was estimated using Monte Carlo program with TCM profiles explicitly modeled. The discrepancy between the estimated organ dose and dose simulated using TCM Monte Carlo program was quantified. We further compared the convolution-based organ dose estimation method with two other strategies with different approaches of quantifying the irradiation field. The proposed convolution-based estimation method showed good accuracy with the organ dose simulated using the TCM Monte Carlo simulation. The average percentage error (normalized by CTDIvol) was generally within 10% across all organs and modulation profiles, except for organs located in the pelvic and shoulder regions. This study developed an improved method that accurately quantifies the irradiation field under TCM scans. The results suggested that organ dose could be estimated in real-time both prospectively (with the localizer information only) and retrospectively (with acquired CT data).

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. The IC was placed at 23 well-distributed holes in the central and peripheral regions of the phantom and dose was recorded for six acquisition protocols with different combinations of minimum kVp (109 and 125 kVp) and z-collimator aperture (full: 22.2 cm; medium: 14.0 cm; small: 8.4 cm). Monte Carlo (MC) simulations were carried out to generate complete 2D dose distributions in the central plane (z = 0). The MC model was validated at the 23 dose points against IC experimental data. The planar dose distributions were then estimated using subsets of the point dose measurements using two proposed methods: (1) the proximity-based weighting method (method 1) and (2) the dose point surface fitting method (method 2). Twenty-eight different dose point distributions with six different point number cases (4, 5, 6, 7, 14, and 23 dose points) were evaluated to determine the optimal number of dose points and their placement in the phantom. The performances of the methods were determined by comparing their results with those of the validated MC simulations. The performances of the methods in the presence of measurement uncertainties were evaluated., Results: The 5-, 6-, and 7-point cases had differences below 2%, ranging from 1.0% to 1.7% for both methods, which is a performance comparable to that of the methods with a relatively large number of points, i.e., the 14- and 23-point cases. However, with the 4-point case, the performances of the two methods decreased sharply. Among the 4-, 5-, 6-, and 7-point cases, the 7-point case (1.0% [±0.6%] difference) and the 6-point case (0.7% [±0.6%] difference) performed best for method 1 and method 2, respectively. Moreover, method 2 demonstrated high-fidelity surface reconstruction with as few as 5 points, showing pixelwise absolute differences of 3.80 mGy (±0.32 mGy). Although the performance was shown to be sensitive to the phantom displacement from the isocenter, the performance changed by less than 2% for shifts up to 2 cm in the x- and y-axes in the central phantom plane., Conclusions: With as few as five points, method 1 and method 2 were able to compute the mean dose with reasonable accuracy, demonstrating differences of 1.7% (±1.2%) and 1.3% (±1.0%), respectively. A larger number of points do not necessarily guarantee better performance of the methods; optimal choice of point placement is necessary. The performance of the methods is sensitive to the alignment of the center of the body phantom relative to the isocenter. In body applications where dose distributions are important, method 2 is a better choice than method 1, as it reconstructs the dose surface with high fidelity, using as few as five points.

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. 40, 111920 (14pp.) (2013)] and is extended to PM and concurrent TCM/PM as well as variable aperture in this work., Methods: Rigorous convolution equations are derived to describe the accumulated dose distributions for TCM, PM, and concurrent TCM/PM. A comparison with scanner-reported CTDI(vol) formulae clearly identifies the source of their differences with the traditional CTDI(vol). Dose distribution simulations using the convolution are provided for a variety of TCM and PM scenarios including a helical shuttle used for perfusion studies (as well as constant mA)-all having the same scanner-reported CTDI(vol). These new convolution simulations for TCM are validated by comparison with their previous discrete summations., Results: These equations show that PM is equivalent to TCM if the pitch variation p(z) is proportional to 1/i(z), where i(z) is the local tube current. The simulations show that the local dose at z depends only weakly on the local tube current i(z) or local pitch p(z) due to scatter from all other locations along z, and that the "local CTDI(vol)(z)" or "CTDI(vol) per slice" do not represent a local dose but rather only a relative i(z) or p(z). The CTDI-paradigm does not apply to shift-variant techniques and the scanner-reported CTDI(vol) for the same lacks physical significance and relevance., Conclusions: While the traditional CTDI(vol) at constant tube current and pitch conveys useful information (the peak dose at the center of the scan length), CTDI(vol) for shift-variant techniques (TCM or PM) conveys no useful information about the associated dose distribution it purportedly represents. On the other hand, the total energy absorbed E ("integral dose") as well as its surrogate DLP remain robust (invariant) with respect to shift-variance, depending only on the total mAs = 〈i〉t0 accumulated during the total beam-on time t0 and aperture a, where 〈i〉 is the average current.

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., ACR DIR), and a method for recognition and correction is provided., Methods: Rigorous methods and equations are presented which describe the dose distributions for stationary-table CT. A comparison with formulae for scanner-reported values of CTDIvol clearly identifies the source of these anomalies., Results: For the stationary table, use of the CTDI100 formula (applicable to a moving phantom only) overestimates the dose due to extra scatter and also includes an overbeaming correction, both of which are nonexistent when the phantom (or patient) is held stationary. The reported DLP remains robust for the stationary phantom., Conclusions: The CTDI-paradigm does not apply in the case of a stationary phantom and simpler nonintegral equations suffice. A method of correction of the currently reported CTDIvol using the approach-to-equilibrium formula H(a) and an overbeaming correction factor serves to scale the reported CTDIvol values to more accurate levels for stationary-table CT, as well as serving as an indicator in the detection of "bad data."

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. Graphical dose simulations are also provided for a variety of TCM tube current distributions (including constant mA), all having the same scanner-reported CTDI(vol)., Results: These convolution equations and simulations show that the local dose at z depends only weakly on the local tube current i(z) due to the strong influence of scatter from all other locations along z, and that the "local CTDI(vol)(z)" does not represent a local dose but rather only a relative i(z) ≡ mA(z). TCM is a shift-variant technique to which the CTDI-paradigm does not apply and its application to TCM leads to a CTDI(vol) of the second kind which lacks relevance., Conclusions: While the traditional CTDI(vol) at constant mA conveys useful information (the peak dose at the center of the scan length), CTDI(vol) of the second kind conveys no useful information about the associated TCM dose distribution it purportedly represents and its physical interpretation remains elusive. On the other hand, the total energy absorbed E ("integral dose") as well as its surrogate DLP remain robust between variable i(z) TCM and constant current i0 techniques, both depending only on the total mAs = {i}t0 = i0t0 during the beam-on time t0.

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., (Copyright © 2012 American College of Radiology. Published by Elsevier Inc. All rights reserved.)

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., high dose perfusion studies using variable (or zero) pitch. In this work, a convolustion-based beam model developed by Dixon et al. [Med. Phys. 32, 3712-3728, (2005)] updated with a scatter LSF kernel (or DSF) derived from a Monte Carlo simulation by Boone [Med. Phys. 36, 4547-4554 (2009)] is used to create an analytical equation for the axial dose profile f(z) in a cylindrical phantom. Using f(z), equations are derived which provide the analytical description of Sconventional (axial and helical) dose, demonstrating its physical underpinnings; and likewise for the peak axial dose f(0) appropriate to stationary phantom cone beam CT, (SCBCT). The methodology can also be applied to dose calculations in shift-variant scan protocols. This paper is an extension of our recent work Dixon and Boone [Med. Phys. 37, 2703-2718 (2010)], which dealt only with the properties of the peak dose f(0), its relationship to CTDI, and its appropriateness to SCBCT., Methods: The experimental beam profile data f(z) of Mori et al. [Med. Phys. 32, 1061-1069 (2005)] from a 256 channel prototype cone beam scanner for beam widths (apertures) ranging from a = 28 to 138 mm are used to corroborate the theoretical axial profiles in a 32 cm PMMA body phantom., Results: The theoretical functions f(z) closely-matched the central axis experimental profile data for all apertures (a = 28 -138 mm). Integration of f(z) likewise yields analytical equations for all the (CTDI-based) dosimetric quantities of conventional CT (including CTDIL itself) in addition to the peak dose f(0) relevant to SCBCT (allowing direct cross-comparison between CT scan modes and mathematical proofs of several hypotheses of practical utility in CT dosimetry). A fast, analytical dose simulator6 is also demonstrated-successfully matching complex dose distributions measured using OSL and film dosimetry., Conclusions: The model described allows one to obtain analytical functions describing both the primary and scatter components of the axial dose profile. This model (using no empirical functions or adjustable fit parameters) provides a good match to the experimental data, as well as a complete analytical description of dose for both conventional (axial and helical) CT and cone beam CT. An efficient method whereby the complete data set for both modalities can be obtained from a single measurement of either CTDI100 or f(0) is illustrated. This method is also flexible--allowing calculation of heretofore unattainable doses for recently-introduced shift-variant protocols [e.g., variable pitch (irregular scan spacing), variable aperture, shuttle mode acquisition, and mA modulation schemes].

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., in cardiac CT) are rapidly proliferating in the clinic, referred to herein as stationary cone beam CT (SCBCT). The integral format of the CTDI paradigm is not appropriate for a stationary phantom, and is not useful for predicting the dose in SCBCT, nor for perfusion studies or CT fluoroscopy. Likewise, the pencil chamber has limited utility in this domain (even one of extended length)., Methods: By demonstrating, both experimentally and theoretically, the match between the dose distribution f(z) for a wide cone beam and that due to an axial scan series D(z), it is shown that the dose on the central ray of the cone beam f(0) is both spatially colocated and numerically equal to the dose predicted by CTDI for the axial series; and thus f(0) is the logical (and unique) choice for a SCBCT dose-descriptor consistent with the CTDI-based dose of conventional CT. This dose f(0) can be readily measured using a conventional (short) ionization chamber. Additionally, Monte Carlo simulations of Boone [J. M. Boone, "Dose spread functions in computed tomography: A Monte Carlo study," Med. Phys. 36, 4547-4554 (2009)], expressed as a scatter LSF (or DSF), allow the application of a convolution-based model [R. L. Dixon, M. T. Munley, and E. Bayram, "An improved analytical model for CT dose simulation with a new look at the theory of CT dose," Med. Phys. 32, 3712-3728 (2005)] of the axial dose profile f(z) for any primary beam width a (any n x T), fan beam and cone beam alike, from a single LSF kernel; its simple form allows the results to be expressed as simple analytical equations. The experimental data of Mori et al. [S. Mori, M. Endo, K. Nishizawa, T. Tsunoo, T. Aoyama, H. Fujiwara, and K. Murase, "Enlarged longitudinal dose profiles in cone-beam CT and the need for modified dosimetry," Med. Phys. 32, 1061-1069 (2005)] from a 256 channel cone beam scanner for a variety of beam widths (28-138 mm) are used to corroborate the theory., Results: Useful commonalities between SCBCT and conventional CT dose are revealed, including a common equilibrium dose parameter A(eq), which is independent of z-collimator aperture a (or n x T), and a common analytical (exponential growth) function H(lambda) describing the relative approach to scatter equilibrium at z = 0 for both modalities (with lambda = a or lambda = scan length L). This function exhibits good agreement with the above-mentioned cone beam data of Mori et al. for H(a) as well as with data H(L) obtained from conventional CT scanning [R. L. Dixon and A. C. Ballard, "Experimental validation of a versatile system of CT dosimetry using a conventional ion chamber: Beyond CTDI100," Med. Phys. 34(8), 3399-3413 (2007)] for the same directly irradiated, phantom length L = a., Conclusions: This methodology and associated mathematical theory provide a physically self-consistent description of dose between stationary phantom CT and conventional CT, and has predictive capabilities which can be used to effect a substantial reduction in data collection; provide a bridge between modalities; and predict the relevant peak doses f(0) for perfusion studies.

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. Potential future directions in radiologic techniques used for studying urolithiasis are also discussed.

This article is an experimental demonstration and authentication of a new method of computed tomography dosimetry [R. L. Dixon, Med. Phys. 30, 1272-1280 (2003)], which utilizes a short, conventional ion chamber rather than a pencil chamber, and which is more versatile than the latter. The value of CTDI100 correctly predicts the accumulated dose only for a total scan length L equal to 100 mm and underestimates the limiting equilibrium dose approached for longer, clinically relevant body scan lengths [R. L. Dixon, Med. Phys. 30, 1272-1280 (2003); K. D. Nakonechny, B. G. Fallone, and S. Rathee, Med. Phys. 32, 98-109 (2005); S. Mori, M. Endo, K. Nishizawa, T. Tsunoo, T. Aoyama, H. Fujiwara, and K. Murase, Med. Phys. 32, 1061-1069 (2005); R. L. Dixon, M. T. Munley, and E. Bayram, Med. Phys. 32, 3712-3728 (2005); R. L. Dixon, Med. Phys. 33, 3973-3976 (2006)]. Dixon [Med. Phys. 30, 1272-1280 (2003)] originally proposed an alternative using a short ion chamber and a helical scan acquisition to collect the same integral for any scan length L (and not limited 100 mm). The primary purpose of this work is to demonstrate experimentally the implementation, robustness, and versatility of this small ion chamber method in measuring the accumulated dose in the body phantom for any desired scan length L (up to the available phantom length) including the limiting equilibrium dose (symbolically CTDIinfinity), and validation of the method against the pencil chamber methodology. Additionally, a simple and robust method for independently verifying the active length of a pencil chamber is described. The results of measurements made in a 400 mm long, 32 cm diameter polymethylmethacrylate body phantom using a small Farmer-type ion chamber and two pencil chambers of lengths l=100 and 150 mm confirm that the two methodologies provide the same dose values at the corresponding scan lengths L=l. The measured equilibrium doses obtained for GE MDCT scanners at 120 kVp are CTDIinfinity = 1.75 CTDI100 on the central axis and 1.22 CTDI100 on the peripheral axes, illustrating a nontrivial shortfall of CTDI100 in that regard and in good agreement with comparable data [S. Mori, M. Endo, K. Nishizawa, T. Tsunoo, T. Aoyama, H. Fujiwara, and K. Murase, Med. Phys. 32, 1061-1069 (2005); J. M. Boone, Med. Phys. 34, 1364-1371 (2007)].

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. Three consecutive slices from the computed tomography scan were analyzed. The basal ganglia had to be visualized on at least 1 slice. Calvarial volume measurement, mean pixel value in each slice, and Hounsfield unit difference between WM and GM, were compared between the thick-skulled and control groups. The mean bone volume of each slice in the thick-skulled group was 55.7, 54.3, and 56 mL, whereas the mean volume of each slice in the normal group was 39.3, 38.5, and 39.9 mL (P < 0.001). In our series, patients with thick skulls had 41% more bone volume than the normal group. The mean skull pixel value in each slice was 935.9 in patients with thick skulls and 987 in patients in the normal group. There was no difference between right and left sides of the same group of patients. Patients with larger volumes of skull have significant decrease in the Hounsfield unit of the GM and WM compared with the control group. As a result, diagnosing any low-contrast brain abnormality including early/subtle infarction in subjects with a thicker calvarium may be more difficult.

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. The model, developed prior to the advent of multidetector CT scanners, is still widely used; however, it does not account for the effect of anode tilt on the penumbra or include the heel effect, both of which are increasingly important for the wider beams (up to 40 mm) of contemporary, multidetector scanners. Additionally, it applied only on (or near) the axis of rotation, and did not incorporate the photon energy spectrum. The improved model described herein transcends all of the aforementioned limitations of the Gagne model, including extension to the peripheral phantom axes. Comparison of simulated and measured dose data provides experimental validation of the model, including verification of the superior match to the penumbra provided by the tilted-anode model, as well as the observable effects on the cumulative dose distribution. The initial motivation for the model was to simulate the quasiperiodic dose distribution on the peripheral, phantom axes resulting from a helical scan series in order to facilitate the implementation of an improved method of CT dose measurement utilizing a short ion chamber, as proposed by Dixon [Med. Phys. 30, 1272-1280 (2003)]. A more detailed set of guidelines for implementing such measurements is also presented in this paper. In addition, some fundamental principles governing CT dose which have not previously been clearly enunciated follow from the model, and a fundamental (energy-based) quantity dubbed "CTDI-aperture" is introduced.

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.

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. It is shown that this measurement would underestimate the equilibrium dose and dose line integral by about 20% in the center of the body phantom, and by about 10% in the center of the head phantom for a 20 mm nominal beam width in a multi-slice scanner. Rather than making the ion chamber even longer to collect the broad scatter tails of the single slice profile, an alternative to the CTDI method is suggested which involves using a small volume ion chamber, and scanning a length of phantom long enough to establish dose equilibrium at the location of the chamber. With a modern CT scanner, such a scan length can be covered in 15 s or less with a helical or axial series, so this method is not significantly more time-consuming than the long chamber method. The method is demonstrated experimentally herein.

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. Various extraurinary diseases found while using NHCT in searching for stone disease are addressed and illustrated. As experience with the use of NHCT has increased, clinicians have broadened the indications for this technique, which has a lower charge than standard CT, beyond the specific evaluation of urinary colic. This indication creep has increased the number of NHCT examinations ordered. It has also reduced the rate of stone positivity and increased the diagnostic yield for extraurinary disease.

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. The dose from leakage radiation due to operation at clinical kVp settings is seen to be orders of magnitude below that predicted by the model in NCRP49. The unshielded secondary radiation dose in air at unit distance and workload is presented as a function of operating potential and for clinical workload distributions. The net transmission of secondary radiations through common shielding materials is presented. Compared to that for the primary beam at the same potential, the transmission of secondary radiation is more penetrating due to the inclusion of leakage radiation that has been hardened by the tube housing. Sample shielding calculations illustrate the utility of this scheme.

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). A shielding model is developed that accounts for attenuation of the primary beam prior to impinging on the structural barrier and which uses a workload which is distributed over a range of clinically realistic operating potentials. The resulting model is as simple to use as that, assuming a single value of the kVp. Sample calculations are performed and the results compared to those from more traditional shielding calculation methods.

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). If patient attenuation is included, the attenuation is more than three orders of magnitude. Transmission factors as well as lead and concrete equivalencies for the various attenuating materials have been determined and included in tabular form. Example calculations for a heavy work load show that only a modest amount of concrete is required in the floor as a primary barrier if attenuation by these materials is taken into consideration (less than 2.5 cm at 80 kVp and less than 4 cm at 100 kVp) and the required secondary barrier may be thicker than the primary barrier.(ABSTRACT TRUNCATED AT 250 WORDS)

Ipazilide fumarate (Win 54, 177-4) is a chemically novel antiarrhythmic agent that prolongs ventricular refractoriness and possesses antiectopic activity. Subchronic (29 days) nonclinical safety evaluation of ipazilide was conducted following oral and iv administration in Sprague-Dawley rats (20-320 mg/kg oral and 1.25-10 mg/kg iv) and 14 and 28 days in beagle dogs (3-30 mg/kg oral and 2.5-20 mg/kg iv). The pharmacokinetic parameters of ipazilide indicate that ipazilide is absorbed (tmax less than or equal to 1 hr) in fasted rats and dogs following single and repeated oral administrations. The apparent elimination half-life in the two species is approximately 1 hr (except in rats at a dosage of 320 mg/kg), suggesting rapid clearance. Increases in liver weights (rats 320 mg/kg) accompanied by the observation of centrilobular hypertrophy of hepatocytes were considered an expression of an adaptive metabolic response of the liver to ipazilide and may be associated with the induction of microsomal enzymes. Duodenal villous atrophy and epithelial hyperplasia (rats, 80 and 320 mg/kg) were interpreted to represent an irritant response to the drug. Local irritation was also observed at the injection site in rats and dogs. Dogs tolerated the oral and the iv administration of ipazilide at dosages of up to 30 and 20 mg/kg, respectively. Despite emesis (oral dogs), which was reduced in frequency following repeated treatment over several weeks, plasma levels in treated dogs (i.e., Cmax 4-5 micrograms/ml) were approximately twice that required to convert spontaneous arrhythmias in the conscious dog model 24 hr after myocardial infarction.(ABSTRACT TRUNCATED AT 250 WORDS)

The objective of toxicological study of a target organ, such as the testis, is to elucidate the qualitative and quantitative toxic effects of a chemical on that organ. The ultimate objective is to assess the toxic effects of a chemical in laboratory animals and extrapolate the pertinent experimental data to man. To accomplish these objectives, one must consider the main factors which may influence and modulate the toxic effects of chemicals in the organ. In the male gonads, such modifying factors are the pharmacokinetic parameters governing the absorption, distribution, activation and detoxification of indirect carcinogens, covalent bindings to macromolecules, and DNA damage as well as DNA repair of damaged germ cells. All of these factors have been presently studied in our laboratory and are discussed in this paper with the exception of covalent bindings to macromolecules.The pharmacokinetic studies demonstrated that the functional blood-testis barrier (BTB) closely resembles the blood-brain barrier in transport characteristics: the permeability of nonelectrolytes and the acidic drugs with pK(a) values depend upon their molecular size and their partition coefficients, respectively. Thus, the functional BTB, restricts the permeability of many foreign compounds to male germ cells. Studies of mixed function oxidases and cytochrome P-450 system in male gonads demonstrated that the presence of AHH, EH, and GSH-ST implicate activation and detoxification of polycyclic hydrocarbons. Thus, active electrophiles may exert significant toxic effects locally within both interstitial and germ cell compartments. The presence of an efficient DNA repair system in premeiotic spermatogenic cells (and not in spermiogenic cells) can further modify both toxic and mutagenic events in the subsequent differentiation of germ cells to mature spermatozoa.

Physiological studies by Setchell and others have described the existence of a blood-testis barrier (BTB) surrounding the seminiferous tubules of the mammalian testis. These studies were initiated to better define the role of the BTB with regard to the penetration of exogenous chemicals to male germ cells. The rete testis was cannulated in rats and fluid was collected. Test chemicals or drugs were usually administered by continuous i.v. infusion. Permeability of nonelectrolytes of various molecular sizes, acidic compounds with varying partition coefficients and pKalpha values, such as salicylic acid, barbiturates, and sulfonamides, across the BTB were studied. Permeability of nonelectrolytes was demonstrated to be dependent upon their molecular size, suggesting bulk flow through water-filled pores. On the other hand, permeability of acidic drugs with varying pKalpha values depended upon their partition coefficients. Transport of these chemicals from blood to seminferous tubules closely resembled their transport from blood to cerebrospinal fluid. It appears that the BTB is a complex multicellular system composed of membranes surrounding the semiferous tubules and the several layers of spermatogenic cells organized within the tubules, which restrict the permeability to the male germ cells of many foreign compounds. This must be borne in mind when extra-polating data from in vitro mutagenic test systems to man.

Exposure of mice to 50, 250, or 1000 ppmm of vinyl chloride (VC) in the air for 6 h/d, 5 d/wk, caused a high incidence of bronchioloalveolar adenoma, mammary gland tumors, and hemangiosarcoma. Mammary gland tumors occurred in the females and included ductular adenocarcinoma and squamous and anaplastic cell carcinomas with metastasis to the lung. Hemangiosarcoma occurred in the liver and, to a lesser extent, in various other organs. The incidence and severity of these tumors increased with the concentration of VC and the length of exposure. Malignant lymphoma involving various organs was observed in several mice. Rats were more resistant to the carcinogenic effects of VC. Exposure of rats to 250 or 1000 ppm of VC caused hemangiosarcoma in the liver. Many rats with hepatic hemangiosarcoma also developed hemangiosarcoma in the lung. Extrahepatic hemangiosarcoma also occasionally occurred in other organs. Exposure to 55 ppm of vinylidene chloride (VDC) caused hepatic hemangiosarcoma and probably bronchioloalveolar adenoma in mice. Hemangiosarcoma also occurred in the mesenteric lymph node or subcutaneous tissue in two rats exposed to 55 ppm of VDC.

Recently the potential toxicity of environmental mercury has become a major concern. Human tissues contain mercury due to daily environmental exposure. Nearly all of the mercury contaminating food is in the form of methylmercury complexes, due to the biotransformation of inorganic mercury. This report compares the reproductive effects of methylmercury hydroxide and mercuric chloride in male mice. The mercuric compounds were administered intraperitoneally once at a dose of 1 mg/kg (based on Hg++ concentration), or spermatogenic cells were exposed in vitro to Hg+ concentrations ranging from 10(-3) to 10(-8)M. Spermatogenic cells were separated for biochemical studies using the velocity sedimentation technique, and in vivo serial mating was used to assess fertility. The effects of CH3Hg+ or Hg++ on the uptake of 3H-thymidine by spermatogonia, 3H-uridine by early elongated spermatids, and 3H-L-leucine by late elongated spermatids were studied. These in vitro experiments indicated that at 1-(-3) m CH2HgOH reduced thymidine incorporation by spermatogonia by 40%, uridine incorporation by elongated spermatids by 39% and L-leucine incorporation by late elongated spermatids by 40%. Results obtained with HgCl2 were similar but of lesser magnitude. In vivo administration of CH3HgOH and HgCl2 significantly inhibited the uptake of thymidine, uridine and L-leucine by their respective spermatogenic cells. Fertility profiles obtained from serial mating studies indicated that the primary effect of CH3HgOH was on spermatogonial cells, premeiotic spermatocytes and early elongated spermatids, with no apparent effect on spermatozoa in testis, peididymis or vas deferentia. HgCl2 also primarily affected spermatogonial and premeiotic cells, but the effect was less than that seen with CH3HgOH. Statistical analysis indicated significant antifertility effects. Inhibition of uptake of thymidine and uridine was well correlated with the functionality of these cells as reflected in the fertility profile, excep for L-leucine uptake. Mercury ion-induced antifertility effects at the dosage used in these experiments are reversible. Thus, these results suggest spermatogenic effects of methylmercury complexes which might have important health consequences in man.

The reproductive toxicologist must be more concerned with the ability of laboratory models to predict human reproductive hazards and to estimate human health risks. Although more than a hundred chemicals have been reported to affect the reproductive capacity of male laboratory animals, fewer than 15 environmental chemicals have been shown conclusively to affect man and many of these are known mutagens, carcinogens or otherwise generally toxic agents. Pharmacokinetic and adaptive factors must be considered. More attention also needs to be directed towards processes other than spermatogenesis and towards mechanisms of toxicity other than cytotoxicity. The male component necessary for successful reproduction depends on a large variety of biological processes working in concert. The ability to assess chemically-induced reproductive effects needs to be refined and modern molecular and cellular approaches should be developed and validated. This paper summarizes aspects of the pharmacokinetic and adaptive factors involved in testicular toxicity, some current laboratory assessment techniques, and newer test procedures such as monoclonal antibodies for sperm surface proteins and the interspecies (human/hamster) sperm penetration assay.

The performance of a new quality control dose monitor for radiation therapy with respect to precision, stability, temperature coefficient, and radiation damage has been extensively evaluated. The results of routine use at several centers are reported.

Prenatal exposure to diethylstilbestrol (DES), a synthetic estrogen, has been associated with a low incidence of vaginal adenocarcinoma as well as a variety of more numerous benign abnormalities in the reproductive tract of human beings and experimental animals. For the purpose of assessing the effects of prenatal exposure to DES on postnatal reproduction tract function, timed pregnant CD-1 mice were treated subcutaneously with doses of DES ranging from 0.01 to 100 microgram/kg/day on days 9 through 16 gestation. The fertility of the female offspring was determined postnatally by a repetitive forced breeding technique. The most striking effect observed was a dose-related decrease in reproductive capacity ranging from minimal subfertility at the lower DES doses to a high frequency of total sterility at the highest DES doses. Reduced reproductive capacity appeared to be a reflection of both a decrease in the total number of litters and smaller litter sizes. A major component of the sterility seen in those females given higher doses of DES was oviductal/ovarian, since the number of ova recovered from the oviductal ampullae after induced ovulation was less than 30% that of controls. In addition, structural abnormalities of the oviduct, uterus, cervix, and vagina were observed, and contributed to infertility. These data suggest that in utero exposure to DES results in permanent impairment of female mouse reproductive capacity. Recent reports of altered pregnancy outcomes in young women who were exposed in utero to DES demonstrate the clinical importance of the findings obtained in mice.