Objective:To compare the dose distribution among CyberKnife, Tomotherapy, Edge, Triology and γ-knife in stereotactic body radiation therapy (SBRT) for pancreatic cancer.Methods:Clinical data of 10 panreatic cancer patients receiving CyberKinife treatment were retrospectively analyzed. The treatment plans were designed by five apparatuses from five centers according to the uniform requirement. All plans were transferred to MIM system for the extraction of parameters, which mainly included D min, D mean and D max of PTV, conformity index (CI), new conformity index (nCI), homogeneity index (HI), gradient index (GI), coverage, D max and dose-volume of the stomach and bowel. Results:The best CI and nCI were obtained in Triology ( P<0.001), and the worst HI was found in γ-knife ( P<0.001). The best GI was found in CyberKnife, followed by γ-knife and Tomotherapy, and Edge showed the worst GI ( P<0.001). The highest D min of PTV was found in both Edge and Triology, while lower D min of PTV was found in CyberKnife and Tomotherapy ( P<0.001). Additionally, γ-knife provided the highest D mean and D max of PTV ( P<0.001). Regarding the organs at risk, the lowest D max and D 5cm 3 of the bowel ( P<0.001), D max of the stomach ( P=0.003), D max( P=0.001), D 5cm 3 ( P<0.001) and D 10cm 3 ( P=0.005) of the duodenum, D max( P<0.001) and D 0.35cm 3 ( P<0.001) of the spinal cord were found in CyberKnife. The highest D max of the bowel was found in γ-knife. Furthermore, the highest D 5cm 3 of the duodenum was demonstrated in Edge ( P<0.001) and Tomotherapy provided the highest D max( P<0.001) and D 0.35cm 3 of the spinal cord ( P<0.001). Conclusions:All five radiotherapy apparatuses can meet the requirement of SBRT for pancreatic cancer. More rapid dose fall-off could be obtained via CyberKnife and γ-knife. Triology and Edge provide better target conformity. CyberKnife can better protect the gastrointestinal tract.

Objective To investigate the causes of false-positive rifampicin resistant results in Xpert MTB/RIF (Xpert) test for samples with extremely low bacterial loads. Methods A total of 346 samples with extremely low bacterial loads and rifampicin-resistance results from Wuhan Pulmonary Hospital between June 2017 and March 2021 were collected. The samples were divided into probe-delayed and probe dropout groups based on amplification results. Mycobacterial culture and proportion method drug susceptibility testing were performed, and Xpert retesting was conducted for strains with discordant drug susceptibility results. Results Out of the 346 samples, 195 samples (56.36%) were positive in culture. Upon Xpert retesting, among the 64 Xpert-resistant but proportion method-sensitive strains, the proportions of samples in the delayed probe group with mutations in the probe D and probe E were 4.55%（1/22） and 13.33%（2/15）, respectively. In the probe dropout group, the proportions of samples with mutations in the probe A and probe E were 75.00% (9/12) and 80.00% (8/10), respectively. The false-positive rifampicin resistance rates in the delayed probe and probe dropout groups were 78.26% (36/46) and 3.36% (5/149), respectively. Conclusion The main reasons for false-positive rifampicin resistance results in the Xpert test for samples with extremely low bacterial loads were probe delay in the D and E probes, followed by low-level drug-resistant mutations in the A and E probes.