Investigating centering, scan length, and arm position impact on radiation dose across 4 countries from 4 continents during pandemic: mitigating key radioprotection issues

Purpose: Optimization of CT scan practices can help achieve and maintain optimal radiation protection. The aim was to assess centering, scan length, and positioning of patients undergoing chest CT for suspected or known COVID-19 pneumonia and to investigate their effect on associated radiation doses. Methods: With respective approvals from institutional review boards, we compiled CT imaging and radiation dose data from four hospitals belonging to four countries (Brazil, Iran, Italy, and USA) on 400 adult patients who underwent chest CT for suspected or known COVID-19 pneumonia between April 2020 and August 2020. We recorded patient demographics and volume CT dose index (CTDIvol) and dose length product (DLP). From thin-section CT images of each patient, we estimated the scan length and recorded the first and last vertebral bodies at the scan start and end locations. Patient mis-centering and arm position were recorded. Data were analyzed with analysis of variance (ANOVA). Results: The extent and frequency of patient mis-centering did not differ across the four CT facilities (>0.09). The frequency of patients scanned with arms by their side (11–40% relative to those with arms up) had greater mis-centering and higher CTDIvol and DLP at 2/4 facilities (p = 0.027–0.05). Despite lack of variations in effective diameters (p = 0.14), there were significantly variations in scan lengths, CTDIvol and DLP across the four facilities (p < 0.001). Conclusions: Mis-centering, over-scanning, and arms by the side are frequent issues with use of chest CT in COVID-19 pneumonia and are associated with higher radiation doses

Investigating centering, scan length, and arm position impact on radiation dose across 4 countries from 4 continents during pandemic: Mitigating key radioprotection issues

Purpose: Optimization of CT scan practices can help achieve and maintain optimal radiation protection. The aim was to assess centering, scan length, and positioning of patients undergoing chest CT for suspected or known COVID-19 pneumonia and to investigate their effect on associated radiation doses. Methods: With respective approvals from institutional review boards, we compiled CT imaging and radiation dose data from four hospitals belonging to four countries (Brazil, Iran, Italy, and USA) on 400 adult patients who underwent chest CT for suspected or known COVID-19 pneumonia between April 2020 and August 2020. We recorded patient demographics and volume CT dose index (CTDIvol) and dose length product (DLP). From thin-section CT images of each patient, we estimated the scan length and recorded the first and last vertebral bodies at the scan start and end locations. Patient mis-centering and arm position were recorded. Data were analyzed with analysis of variance (ANOVA). Results: The extent and frequency of patient mis-centering did not differ across the four CT facilities (>0.09). The frequency of patients scanned with arms by their side (11�40 relative to those with arms up) had greater mis-centering and higher CTDIvol and DLP at 2/4 facilities (p = 0.027�0.05). Despite lack of variations in effective diameters (p = 0.14), there were significantly variations in scan lengths, CTDIvol and DLP across the four facilities (p < 0.001). Conclusions: Mis-centering, over-scanning, and arms by the side are frequent issues with use of chest CT in COVID-19 pneumonia and are associated with higher radiation doses. © 202

Measuring cytotoxicity by bioluminescence imaging outperforms the standard chromium-51 release assay.

The chromium-release assay developed in 1968 is still the most commonly used method to measure cytotoxicity by T cells and by natural killer cells. Target cells are loaded in vitro with radioactive chromium and lysis is determined by measuring chromium in the supernatant released by dying cells. Since then, alternative methods have been developed using different markers of target cell viability that do not involve radioactivity. Here, we compared and contrasted a bioluminescence (BLI)-based cytotoxicity assay to the standard radioactive chromium-release assay using an identical set of effector cells and tumor target cells. For this, we stably transduced several human and murine tumor cell lines to express luciferase. When co-cultured with cytotoxic effector cells, highly reproducible decreases in BLI were seen in an effector to target cell dose-dependent manner. When compared to results obtained from the chromium release assay, the performance of the BLI-based assay was superior, because of its robustness, increased signal-to-noise ratio, and faster kinetics. The reduced/delayed detection of cytotoxicity by the chromium release method was attributable to the association of chromium with structural components of the cell, which are released quickly by detergent solubilization but not by hypotonic lysis. We conclude that the (BLI)-based measurement of cytotoxicity offers a superior non-radioactive alternative to the chromium-release assay that is more robust and quicker to perform

Assay characteristics of the chromium release assay vs. BLI assay.

<p>The spontaneous death, maximal killing, range, and the signal to noise (max:min) ratios measured by ⁵¹Cr release and BLI are shown. Results are presented as mean ± SD of three independent experiments.</p><p>* p<0.01 by Student t test.</p

Measurement of chromium release and luciferase activity in cells lysed by water or by 1% NP40.

<p>Three luciferase-transduced human cell lines (K562, UCI191 and U266) and 3 mouse cell lines (P815, YAC1, and A20) were labeled with radioactive chromium for 4 hours. The cells were lysed in water or 1% NP40 for 4 hours. (A) Chromium release in the supernatant of cells lysed in water or in 1% NP40 was determined. (B) Luciferase activity was detected by BLI in cells lysed in water or in 1% NP40 was determined. The results are represented as mean ± SD of n = 3–4 independent experiments. * p<0.001 by Wilcoxon Rank test.</p

Comparison of cytotoxicity obtained at 2 hours by the chromium release method and BLI method.

<p>Luciferase-transduced human and mouse cell lines were co-cultured with human or mouse effector cells for 2 hours at various E:T ratios. The % specific lysis of the human cell lines, (A) K562, (B) U266, and (C) UCI101 obtained by the chromium release assay (closed circles) or the BLI assay (open circles) is plotted against multiple E:T ratios. The % specific lysis of the human cell lines, (D) P815, (E) YAC1, (F) EL-4, and (G) A20 obtained by the chromium release assay (closed circles) or the BLI assay (open circles) is plotted against multiple E:T ratios. Results are represented as mean ± SD of n = 3 independent experiments. The p values obtained from the statistical analysis performed by permutated two-way ANOVA are shown in each graph.</p

Comparison of cytotoxicity obtained at 4 hours by the chromium release and BLI method.

<p>Luciferase-transduced human and mouse cell lines were co-cultured with human or mouse effector cells for 4 hours at various E: T ratios. The % specific lysis of the human cell lines, (A) K562, (B) U266, and (C) UCI101 obtained by the chromium release assay (closed circles) or the BLI assay (open circles) is plotted against multiple E:T ratios. The % specific lysis of the murine cell lines, (D) P815, (E) YAC1, (F) EL-4, and (G) A20 obtained by the chromium release assay (closed circles) or the BLI assay (open circles) is plotted against multiple E:T ratios. Results are represented as mean ± SD of n = 3 independent experiments. The p values obtained from the statistical analysis performed by permutated two-way ANOVA are shown in each graph.</p

Comparison of cytotoxicity obtained at 4 hours by the chromium release and BLI method at higher E:T ratios.

<p>Luciferase-transduced the YAC1 cell line was co-cultured with mouse effector cells for 4 hours at various E:T ratios ranging from 100∶1 to 20∶1. The % specific lysis obtained by the chromium release assay (closed circles) or the BLI assay (open circles) is plotted against multiple E:T ratios. Results are represented as mean ± SD of triplicate values. One representative of 2 independent experiments is shown. The p value obtained from the statistical analysis performed permutated two-way ANOVA is shown.</p

NKG2D expression by CD8+ T cells contributes to GVHD and GVT effects in a murine model of allogeneic HSCT.

In allogeneic hematopoietic stem cell transplantation (HSCT), controlling graft-versus-host disease (GVHD) while maintaining graft-versus-tumor (GVT) responses is of critical importance. Using a mouse model of allogeneic HSCT, we hereby demonstrate that NKG2D expression by CD8(+) T cells plays a major role in mediating GVHD and GVT effects by promoting the survival and cytotoxic function of CD8(+) T cells. The expression of NKG2D ligands was not induced persistently on normal tissues of allogeneic HSCT-recipient mice treated with anti-NKG2D antibody, suggesting that transient NKG2D blockade might be sufficient to attenuate GVHD and allow CD8(+) T cells to regain their GVT function. Indeed, short-term treatment with anti-NKG2D antibody restored GVT effects while maintaining an attenuated GVHD state. NKG2D expression was also detected on CD8(+) T cells from allogeneic HSCT patients and trended to be higher in those with active GVHD. Together, these data support a novel role for NKG2D expression by CD8(+) T cells during allogeneic HSCT, which could be potentially therapeutically exploited to separate GVHD from GVT effects