Objective To explore the main factors affecting the MV imager projection offset in the machine performance check(MPC)for Varian Vital Beam linear accelerator.Methods The MV imager projection offsets in the MPC after repairing the MV imaging arm encoder of shoulder motor,locking the treatment couch,and isocenter calibration were analyzed.Results MPC results revealed that the MV imager projection offset after repairing the MV imaging arm encoder of shoulder motor was(0.310±0.001)mm,significantly less than(0.450±0.010)mm in the blank group.The difference in MV imager projection offset between the isocenter calibration group and the blank group was trivial.The MV imager projection offset after locking the treatment couch was(0.240±0.030)mm,significantly less than(0.450±0.010)mm in the blank group.When MPC was carried out after repairing the imaging arm encoder and performing isocenter calibration,there was no significant statistical difference in MV imager center offset between the locked and unlocked treatment couch.Conclusion The damage of MV imaging arm encoder of shoulder motor is the main factor causing abnormal MV imager projection offsets.Locking the treatment couch before the MV imaging center check can reduce the results,but it cannot eliminate the MV imager projection offset.

Objective To investigate the association between the value of α-thalassemia minor and the outcomes in pregnant women.Methods A total of 445 pregnant women with α-thalassemia minor were selected as thalassemia group in the Pingguo County Maternal and Child Health Hospital of Guangxi from January 2011 to December 2015,with ratio of 1 ∶ 4 healthy pregnant women was randomly recruited as non-thalassemia group.Clinical characteristics and pregnancy outcomes of the two groups were retrospectively analyzed using methods including t test,x2 test,and logistic regression model and ROC curve.Results There were no significant differences noticed in factors as age,BMI,gestational age and educational level of the two groups.Hemoglobin of the thalassemia group was significantly lower than that of the non-thalassemia group (P＜0.001).Differences on parity,ethnicities or occupation were statistically significant.Results from univariate analysis showed that the proportions of low birth weight,small for date infant and 1 min Apgar score ＜7 were higher in the thalassemia group,but the ratio of adverse pregnancy outcomes was comparable on parameters as preterm birth,stillbirth,macrosomia.Findings from the unconditional logistic regression showed that pregnancy complicated with α-thalassemia minor appeared a risk for both newboms with low birth weight (aOR=2.29,95％CI:1.32-3.95) and small for date infant (aOR=2.11,95％ CI:1.16-3.84).The ROC curve showed that α-thalassemia minor combined with multiple indicators presented a certain predictive value on neonatal birth weight.Conclusion Pregnancy complicated with α-thalassemia minor was likely to increase the risk of birth weight loss in newborns,suggesting that prenatal care for pregnant women with thalassemia be strengthened,in order to reduce the incidence of adverse pregnancy outcomes.