简介：AbstractBackground:The effects of oral contrast agents (OCAs) on dosimetry have not been studied in detail. Therefore, this study aimed to examine the influence of OCAs on dose calculation in volumetric-modulated arc therapy plans for rectal cancer.Methods:From 2008 to 2016, computed tomography (CT) images were obtained from 33 rectal cancer patients administered OCA with or without intravenous contrast agent (ICA) and 14 patients who received no contrast agent. CT numbers of organs at risk were recorded and converted to electronic densities. Volumetric-modulated arc therapy plans were designed before and after the original densities were replaced with non-enhanced densities. Doses to the planned target volume (PTV) and organs at risk were compared between the plans.Results:OCA significantly increased the mean and maximum densities of the bowels, while the effects of ICA on these parameters depended on the blood supply of the organs. With OCA, the actual doses for PTV were significantly higher than planned and doses to the bowel increased significantly although moderately. However, the increase in the volume receiving a high-range doses was substantial (the absolute change of intestine volume receiving ≥52 Gy: 1.46 [0.05-3.99, cubic centimeter range: -6.74 to 128.12], the absolute change of colon volume receiving ≥50 Gy: 0.34 [0.01-1.53 cc, range: -0.08 to 3.80 cc]. Dose changes due to ICA were insignificant. Pearson correlation showed that dose changes were significantly correlated with a high intestinal volume within or near the PTV (ρ > 0.5, P < 0.05) and with the density of enhanced intestine (ρ > 0.3, P < 0.05).Conclusions:Contrast agents applied in simulation cause underestimation of doses in actual treatment. The overdose due to ICA was slight, while that due to OCA was moderate. The bowel volume receiving ≥50Gy was dramatically increased when OCA within the bowel was absent. Physicians should be aware of these issues if the original plan is barely within clinical tolerance or if a considerable volume of enhanced intestine is within or near the PTV.

简介：AbstractBackground:Practitioners and researchers in the midst of overwhelming coronavirus disease 2019 (COVID-19) outbreaks are calling for new ways of looking at such pandemics, with an emphasis on human behavior and holistic considerations. Viral outbreaks are characterized by socio-behaviorally-oriented public health efforts aimed at reducing exposure and prevention of morbidity/mortality once infected. These efforts involve different points-of-view, generally, than do those aimed to understand the virus' natural history. Rampant spread of SARS-CoV-2infection in cities clearly signals that urban areas contain conditions favorable for rapid transmission of the virus.Main text:The Critical Medical Ecology model is a multidimensional, multilevel way of viewing pandemics comprehensively, rooted simultaneously in microbiology and in anthropology, with shared priority for evolution, context, stressors, homeostasis, adaptation, and power relationships. Viewing COVID-19 with a Critical Medical Ecological lens suggests three important interpretations: 1) COVID-19 is equally — if not more — a socially-driven disease as much as a biomedical disease, 2) the present interventions available for primary prevention of transmission are social and behavioral interventions, and 3) wide variation in COVID-19 hospitalization/death rates is not expected to significantly be attributable to a more virulent and rapidly-evolving virus, but rather to differences in social and behavioral factors — and power dynamics — rather than (solely) biological and clinical factors. Cities especially are challenged due to logistics and volume of patients, and lack of access to sustaining products and services for many residents living in isolation.Conclusions:In the end, SARS-CoV-2 is acting upon dynamic social human beings, entangled within structures and relationships that include but extend far beyond their cells, and in fact beyond their own individual behavior. As a comprehensive way of thinking, the Critical Medical Ecology model helps identify these elements and dynamics in the context of ecological processes that create, shape, and sustain people in their multidimensional, intersecting environments.