Choice of tube extremity for emission of the lowest radiation dose in pediatric patients

AIMS: To compare the dosage of radiation the thyroid and gonad glands receive in pediatric patients undergoing chest X-rays, in distinct positions, towards the goal of developing of an X-ray tube positioning protocol. METHODS: A randomized controlled clinical trial was carried out in the Pediatric Intensive Care Unit (PICU) at the Institute of Cardiology/University Foundation of Cardiology of Rio Grande do Sul, Brazil from June 2014 to September 2016. Patients were divided into two groups. One group was positioned with the thyroid gland facing the anode end of an X-ray tube, and in the other group the thyroid gland faced the cathode end. Radiographs were evaluated by five observers, following criteria recommended by the Commission of the European Communities (CEC). RESULTS: Forty-eight pediatric patients, with a mean age of 2.0 ± 1.3 years, participated in this study. Based on the evaluation of 48 images, it was determined that the thyroid and gonad glands facing the cathode were exposed to 13.3 ± 3.1 μGy and 13.5 ± 4.1 μGy of radiation, respectively (p = 0.008). Additionally, the thyroid and gonad glands facing the anode were exposed to 11.7 ± 3.1 μGy and 12.7 ± 3.1 μGy of radiation, respectively (p = 0.007). The mean input dose in the center of the chest was 20.8 ± 9.6 μGy in both positions. DISCUSSION: The proximity of the thyroid gland to the cathode end of the X-ray tube appears to be related to the dosage of ionizing radiation. Adverse effects associated with exposure to ionizing radiation could be minimized by positioning the thyroid gland to the anodic end of the X-ray tube. CONCLUSION: Patients should be placed facing the anode end of the X-ray tube when taking thoracic X-rays, in order to reduce radiation exposure to the thyroid and gonad glands. ClinicalTrials.gov Identifier: NCT02925936.