AAPM Medical physics practice guideline 15.A: Peer review in clinical physics.

The American Association of Physicists in Medicine (AAPM) is a nonprofit professional society whose primary purposes are to advance the science, education, and professional practice of medical physics. The AAPM has more than 8000 members and is the principal organization of medical physicists in the United States. The AAPM will periodically define new practice guidelines for medical physics practice to help advance the science of medical physics and to improve the quality of service to patients throughout the United States. Existing medical physics practice guidelines will be reviewed for the purpose of revision or renewal, as appropriate, on their fifth anniversary or sooner. Each medical physics practice guideline represents a policy statement by the AAPM, has undergone a thorough consensus process in which it has been subjected to extensive review, and requires the approval of the Professional Council. The medical physics practice guidelines recognize that the safe and effective use of diagnostic and therapeutic radiology requires specific training, skills, and techniques, as described in each document. Reproduction or modification of the published practice guidelines and technical standards by those entities not providing these services is not authorized. The following terms are used in the AAPM practice guidelines: Must and Must Not: Used to indicate that adherence to the recommendation is considered necessary to conform to this practice guideline. While must is the term to be used in the guidelines, if an entity that adopts the guideline has shall as the preferred term, the AAPM considers that must and shall have the same meaning. Should and Should Not: Used to indicate a prudent practice to which exceptions may occasionally be made in appropriate circumstances.

Patient Radiation Doses in IR Procedures: The American College of Radiology Dose Index Registry-Fluoroscopy Pilot.

PURPOSE: To update normative data on fluoroscopy dose indices in the United States for the first time since the Radiation Doses in Interventional Radiology study in the late 1990s. MATERIALS AND METHODS: The Dose Index Registry-Fluoroscopy pilot study collected data from March 2018 through December 2019, with 50 fluoroscopes from 10 sites submitting data. Primary radiation dose indices including fluoroscopy time (FT), cumulative air kerma (Ka,r), and kerma area product (PKA) were collected for interventional radiology fluoroscopically guided interventional (FGI) procedures. Clinical facility procedure names were mapped to the American College of Radiology (ACR) common procedure lexicon. Distribution parameters including the 10th, 25th, 50th, 75th, 95th, and 99th percentiles were computed. RESULTS: Dose indices were collected for 70,377 FGI procedures, with 50,501 ultimately eligible for analysis. Distribution parameters are reported for 100 ACR Common IDs. FT in minutes, Ka,r in mGy, and PKA in Gy-cm2 are reported in this study as (n; median) for select ACR Common IDs: inferior vena cava filter insertion (1,726; FT: 2.9; Ka,r: 55.8; PKA: 14.19); inferior vena cava filter removal (464; FT: 5.7; Ka,r: 178.6; PKA: 34.73); nephrostomy placement (2,037; FT: 4.1; Ka,r: 39.2; PKA: 6.61); percutaneous biliary drainage (952; FT: 12.4; Ka,r: 160.5; PKA: 21.32); gastrostomy placement (1,643; FT: 3.2; Ka,r: 29.1; PKA: 7.29); and transjugular intrahepatic portosystemic shunt placement (327; FT: 34.8; Ka,r: 813.0; PKA: 181.47). CONCLUSIONS: The ACR DIR-Fluoro pilot has provided state-of-the-practice statistics for radiation dose indices from IR FGI procedures. These data can be used to prioritize procedures for radiation optimization, as demonstrated in this work.

Patient Radiation Doses in Interventional Radiology Procedures: Comparison of Fluoroscopy Dose Indices between the American College of Radiology Dose Index Registry-Fluoroscopy Pilot and the Radiation Doses in Interventional Radiology Study.

PURPOSE: To compare radiation dose index distributions for fluoroscopically guided interventions in interventional radiology from the American College of Radiology (ACR) Fluoroscopy Dose Index Registry (DIR-Fluoro) pilot to those from the Radiation Doses in Interventional Radiology (RAD-IR) study. MATERIALS AND METHODS: Individual and grouped ACR Common identification numbers (procedure types) from the DIR-Fluoro pilot were matched to procedure types in the RAD-IR study. Fifteen comparisons were made. Distribution parameters, including the 10th, 25th, 50th, 75th, and 95th percentiles, were compared for fluoroscopy time (FT), cumulative air kerma (Ka,r), and kerma area product (PKA). Two derived indices were computed using median dose indices. The procedure-averaged reference air kerma rate (Ka,r¯) was computed as Ka,r / FT. The procedure-averaged x-ray field size at the reference point (Ar) was computed as PKA / (Ka,r × 1,000). RESULTS: The median FT was equally likely to be higher or lower in the DIR-Fluoro pilot as it was in the RAD-IR study, whereas the maximum FT was almost twice as likely to be higher in the DIR-Fluoro pilot than it was in the RAD-IR study. The median Ka,r was lower in the DIR-Fluoro pilot for all procedures, as was median PKA. The maximum Ka,r and PKA were more often higher in the DIR-Fluoro pilot than in the RAD-IR study. Ka,r¯ followed the same pattern as Ka,r, whereas Ar was often greater in DIR-Fluoro. CONCLUSIONS: The median dose indices have decreased since the RAD-IR study. The typical Ka,r rates are lower, a result of the use of lower default dose rates. However, opportunities for quality improvement exist, including renewed focus on tight collimation of the imaging field of view.

Through-the-Glass Portable Radiography of Patients in Isolation Units: Experience During the COVID-19 Pandemic.

OBJECTIVE. To reduce staff exposure to infection and maintain operational efficiency, we have developed a protocol to image patients using portable chest radiography through the glass of an isolation room. This technique is safe and easy to implement. Images are of comparable quality to standard portable radiographs. CONCLUSION. This protocol, used routinely by our department during the COVID-19 pandemic, can be applied to any situation in which the patient is placed in isolation.

PET Measures of D1, D2, and DAT Binding Are Associated With Heightened Tactile Responsivity in Rhesus Macaques: Implications for Sensory Processing Disorder.

Sensory processing disorder (SPD), a developmental regulatory condition characterized by marked under- or over-responsivity to non-noxious sensory stimulation, is a common but poorly understood disorder that can profoundly affect mood, cognition, social behavior and adaptive life skills. Little is known about the etiology and neural underpinnings. Clinical research indicates that children with SPD show greater prevalence of difficulties in complex cognitive behavior including working memory, behavioral flexibility, and regulation of sensory and affective functions, which are related to prefrontal cortex (PFC), striatal, and midbrain regions. Neuroimaging may provide insight into mechanisms underlying SPD, and animal experiments provide important evidence that is not available in human studies. Rhesus monkeys (N = 73) were followed over a 20-year period from birth into old age. We focused on a single sensory modality, the tactile system, measured at 5-7 years, because of its critical importance for nourishment, attachment, and social reward in development. Positron emission tomography imaging was conducted at ages 12-18 years to quantify the availability of the D1 and D2 subtypes of the DA receptor (D1R and D2R), and the DA transporter (DAT). Heightened tactile responsivity was related to (a) elevated D1R in PFC overall, including lateral, ventrolateral, medial, anterior cingulate (aCg), frontopolar, and orbitofrontal (OFC) subregions, as well as nucleus accumbens (Acb), (b) reduced D2R in aCg, OFC, and substantia nigra/ventral tegmental area, and (c) elevated DAT in putamen. These findings suggest a mechanism by which DA pathways may be altered in SPD. These pathways are associated with reward processing and pain regulation, providing top-down regulation of sensory and affective processes. The balance between top-down cognitive control in the PFC-Acb pathway and bottom-up motivational function of the VTA-Acb-PFC pathway is critical for successful adaptive function. An imbalance in these two systems might explain DA-related symptoms in children with SPD, including reduced top-down regulatory function and exaggerated responsivity to stimuli. These results provide more direct evidence that SPD may involve altered DA receptor and transporter function in PFC, striatal, and midbrain regions. More work is needed to extend these results to humans.

Rhesus Macaque Brain Atlas Regions Aligned to an MRI Template.

To aid in the analysis of rhesus macaque brain images, we aligned digitized anatomical regions from the widely used atlas of Paxinos et al. to a published magnetic resonance imaging (MRI) template based on a large number of subjects. Digitally labelled atlas images were aligned to the template in 2D and then in 3D. The resulting grey matter regions appear qualitatively to be well registered to the template. To quantitatively validate the procedure, MR brain images of 20 rhesus macaques were aligned to the template along with regions drawn by hand in striatal and cortical areas in each subject's MRI. There was good geometric overlap between the hand drawn regions and the template regions. Positron emission tomography (PET) images of the same subjects showing uptake of a dopamine D2 receptor ligand were aligned to the template space, and good agreement was found between tracer binding measures calculated using the hand drawn and template regions. In conclusion, an anatomically defined set of rhesus macaque brain regions has been aligned to an MRI template and has been validated for analysis of PET imaging in a subset of striatal and cortical areas. The entire set of over 200 regions is publicly available at https://www.nitrc.org/ . Graphical Abstract ᅟ.

Moderate-level prenatal alcohol exposure induces sex differences in dopamine d1 receptor binding in adult rhesus monkeys.

BACKGROUND: We examined the effects of moderate prenatal alcohol exposure and/or prenatal stress exposure on (D1 R) binding in a non human primate model. The dopamine D1 R is involved in executive function, and it may play a role in cognitive behavioral deficits associated with prenatal alcohol and/or stress exposure. Little is known, however, about the effects of prenatal alcohol and/or stress exposure on the D1 R. We expected that prenatal insults would lead to alterations in D1 R binding in prefrontal cortex (PFC) and striatum in adulthood. METHODS: Rhesus macaque females were randomly assigned to moderate alcohol exposure and/or mild prenatal stress as well as a control condition during pregnancy. Thirty-eight offspring were raised identically and studied as adults by noninvasive in vivo neuroimaging using positron emission tomography with the D1 antagonist radiotracer [(11) C]SCH 23390. Radiotracer binding in PFC and striatum was evaluated by 2 (alcohol) × 2 (stress) × 2 (sex) analysis of variance. RESULTS: In PFC, a significant alcohol × sex interaction was observed with prenatal alcohol exposure leading to increased [(11) C]SCH 23390 binding in male monkeys. No main effect of prenatal alcohol or prenatal stress exposure was observed. CONCLUSIONS: These results suggest that prenatal alcohol exposure results in long-term increases in prefrontal dopamine D1 R binding in males. This may help explain gender differences in the prevalence of neurodevelopmental disorders consequent to prenatal alcohol exposure.

Prenatal stress induces increased striatal dopamine transporter binding in adult nonhuman primates.

BACKGROUND: To determine the effects in adult offspring of maternal exposure to stress and alcohol during pregnancy, we imaged striatal and midbrain dopamine transporter (DAT) binding by positron emission tomography in rhesus monkeys (Macaca mulatta). We also evaluated the relationship between DAT binding and behavioral responses previously found to relate to dopamine D2 receptor density (responsivity to tactile stimuli, performance on a learning task, and behavior during a learning task). METHODS: Subjects were adult offspring derived from a 2 × 2 experiment in which pregnant monkeys were randomly assigned to control, daily mild stress exposure (acoustic startle), voluntary consumption of moderate-level alcohol, or both daily stress and alcohol. Adult offspring (n = 38) were imaged by positron emission tomography with the DAT ligand [(18)F]2ß-carbomethoxy-3ß-(4-chlorophenyl)-8-(2-fluoroethyl)-nortropane ([(18)F]FECNT). RESULTS: Results showed that prenatal stress yielded an overall increase of 15% in [(18)F]FECNT binding in the striatum (p = .016), 17% greater binding in the putamen (p = .012), and 13% greater binding in the head of the caudate (p = .028) relative to animals not exposed to prenatal stress. Striatal [(18)F]FECNT binding correlated negatively with habituation to repeated tactile stimulation and positively with tactile responsivity. There were no significant effects of prenatal alcohol exposure on [(18)F]FECNT binding. CONCLUSIONS: Maternal exposure to mild daily stress during pregnancy yielded increases in striatal DAT availability that were apparent in adult offspring and were associated with behavioral characteristics reflecting tactile hyperresponsivity, a condition associated with problem behaviors in children.

5-HT1A sex based differences in Bmax, in vivo KD, and BPND in the nonhuman primate.

UNLABELLED: Serotonin (5-HT) dysfunction has been implicated in neuropsychiatric illnesses and may play a pivotal role in the differential prevalence of depression between the sexes. Previous PET studies have revealed sex-based differences in 5-HT1A binding potential (BPND). The binding potential is a function of the radioligand-receptor affinity (1/KDapp), and receptor density (Bmax). In this work, we use a multiple-injection (MI) PET protocol and the 5-HT1A receptor antagonist, [(18)F]mefway, to compare sex-based differences of in vivo affinity, Bmax, and BPND in rhesus monkeys. METHODS: PET [(18)F]mefway studies were performed on 17 (6m, 11f) rhesus monkeys using a 3-injection protocol that included partial saturation injections of mefway. Compartmental modeling was performed using a model to account for non-tracer doses of mefway for the estimation of KDapp and Bmax. BPND estimates were also acquired from the first injection (high specific activity [(18)F]mefway, 90-minute duration) for comparison using the cerebellum (CB) as a reference region. Regions of interest were selected in 5-HT1A binding regions of the hippocampus (Hp), dorsal anterior cingulate cortex (dACC), amygdala (Am), and raphe nuclei (RN). RESULTS: Female subjects displayed significantly (*p<0.05) lower KDapp in the Hp (-32%), Am (-38%), and RN (-37%). Only the Hp displayed significant differences in Bmax with females having a Bmax of -29% compared to males. Male subjects demonstrated significantly lower BPND measurements in the Am (14%) and RN (29%). CONCLUSION: These results suggest that the higher BPND values found in females are the result of lower [(18)F]mefway KDapp. Although a more experimentally complex measurement, separate assay of KDapp and Bmax provides a more sensitive measure than BPND to identify the underlying differences between females and males in 5-HT1A function.

Measurement of 5-HT(1A) receptor density and in-vivo binding parameters of [(18)F]mefway in the nonhuman primate.

The goal of this work was to characterize the in-vivo behavior of [(18)F]mefway as a suitable positron emission tomography (PET) radiotracer for the assay of 5-hydroxytryptamine(1A) (5-HT(1A)) receptor density (B(max)). Six rhesus monkeys were studied using a multiple-injection (M-I) protocol consisting of three sequential bolus injections of [(18)F]mefway. Injection times and amounts of unlabeled mefway were optimized for the precise measurement of B(max) and specific binding parameters k(off) and k(on) for estimation of apparent K(D). The PET time series were acquired for 180 minutes with arterial sampling performed throughout. Compartmental analysis using the arterial input function was performed to obtain estimates for K(1), k(2), k(off), B(max), and K(Dapp) in the cerebral cortex and raphe nuclei (RN) using a model that accounted for nontracer doses of mefway. Averaged over subjects, highest binding was seen in the mesial temporal and dorsal anterior cingulate cortices with B(max) values of 42±8 and 36±8 pmol/mL, respectively, and lower values in the superior temporal cortex, RN, and parietal cortex of 24±4, 19±4, and 13±2 pmol/mL, respectively. The K(Dapp) of mefway for the 5-HT(1A) receptor sites was 4.3±1.3 nmol/L. In conclusion, these results show that M-I [(18)F]mefway PET experiments can be used for the in-vivo measurement of 5-HT(1A) receptor density.

High-affinity dopamine D2/D3 PET radioligands 18F-fallypride and 11C-FLB457: a comparison of kinetics in extrastriatal regions using a multiple-injection protocol.

(18)F-Fallypride and (11)C-FLB457 are commonly used PET radioligands for imaging extrastriatal dopamine D(2)/D(3) receptors, but differences in their in vivo kinetics may affect the sensitivity for measuring subtle changes in receptor binding. Focusing on regions of low binding, a direct comparison of the kinetics of (18)F-fallypride and (11)C-FLB457 was made using a MI protocol. Injection protocols were designed to estimate K(1), k(2), f(ND)k(on), B(max), and k(off) in the midbrain and cortical regions of the rhesus monkey. (11)C-FLB457 cleared from the arterial plasma faster and yielded a ND space distribution volume (K(1)/k(2)) that is three times higher than (18)F-fallypride, primarily due to a slower k(2) (FAL:FLB; k(2)=0.54 min(-1):0.18 min(-1)). The dissociation rate constant, k(off), was slower for (11)C-FLB457, resulting in a lower K(Dapp) than (18)F-fallypride (FAL:FLB; 0.39 nM:0.13 nM). Specific D(2)/D(3) binding could be detected in the cerebellum for (11)C-FLB457 but not (18)F-fallypride. Both radioligands can be used to image extrastriatal D(2)/D(3) receptors, with (11)C-FLB457 providing greater sensitivity to subtle changes in low-receptor-density cortical regions and (18)F-fallypride being more sensitive to endogenous dopamine displacement in medium-to-high-receptor-density regions. In the presence of specific D(2)/D(3) binding in the cerebellum, reference region analysis methods will give a greater bias in BP(ND) with (11)C-FLB457 than with (18)F-fallypride.