Response to Dr. Frush

The effectiveness of 4DCT in children and adults: A pooled analysis

BACKGROUND

While four-dimensional computed tomography (4DCT) is extensively used in adults, reluctance remains to use 4DCT in children. Day-to-day (interfractional) variability and irregular respiration (intrafractional variability) have shown to be limiting factors of 4DCT effectiveness in adults. In order to evaluate 4DCT applicability in children, the purpose of this study is to quantify inter- and intrafractional variability of respiratory motion in children and adults. The pooled analysis enables a solid comparison to reveal if 4DCT application for planning purposes in children could be valid.

METHODS/MATERIALS

We retrospectively included 90 patients (45 children and 45 adults), for whom the diaphragm was visible on abdominal/thoracic free-breathing cone beam CTs (480 pediatric, 524 adult CBCTs). For each CBCT, the cranial-caudal position of end-exhale and end-inhale positions of the right diaphragm dome were manually selected in the projection images. The difference in position between both phases defines the amplitude. Cycle time equaled inspiratory plus expiratory time. We analyzed the variability of the inter- and intrafractional respiratory-induced diaphragm motion.

RESULTS

Ranges of respiratory motion characteristics were large in both children and adults (amplitude: 4-17 vs 5-24 mm, cycle time 2.1-3.9 vs 2.7-6.5 s). The mean amplitude was slightly smaller in children than in adults (10.7 vs 12.3 mm; P = 0.06). Interfractional amplitude variability was statistically significantly smaller in children than in adults (1.4 vs 2.2 mm; P = 0.00). Mean cycle time was statistically significantly shorter in children (2.9 vs 3.6 s; P = 0.00). Additionally, intrafractional cycle time variability was statistically significantly smaller in children (0.5 vs 0.7 s; P = 0.00).

CONCLUSIONS

Overall variability is smaller in children than in adults, indicating that respiratory motion is more regular in children than in adults. This implies that a single pretreatment 4DCT could be a good representation of daily respiratory motion in children and will be at least equally beneficial for planning purposes as it is in adults.

Radiation Exposure of Premature Infants Beyond the Perinatal Period

OBJECTIVES

To determine the odds of premature compared with term infants exceeding the recommended radiation exposure threshold in the first year after discharge from birth hospitalization.

METHODS

In this observational retrospective cohort study, we compared the radiation exposure of premature and term infants between 2008 and 2015 in an urban hospital system. The primary outcome was crossing the radiation exposure threshold of 1 millisievert. We assessed prematurity's effect on this outcome with multivariable logistic regression.

RESULTS

In our study, 20 049 term and 2047 preterm infants met inclusion criteria. The population was approximately one-half female, predominantly multiracial or people of color (40% African American and 44% multiracial), and of low socioeconomic status. Premature infants had 2.25 times greater odds of crossing the threshold compared with term infants after adjustment for demographics (95% confidence interval [CI]: 1.66-3.05). Adjustment for complex chronic conditions, which are validated metrics of pediatric chronic illness, attenuated this association; however, premature infants still had 1.58 times greater odds of crossing the threshold (95% CI: 1.16-2.15). When the final model was analyzed by degree of prematurity, very preterm and extremely preterm infants were significantly more likely to cross the threshold (1.85 [95% CI: 1.03-3.32] and 2.53 [95% CI: 1.53-4.21], respectively), whereas late preterm infants were not (1.14 [95% CI: 0.73-1.78]).

CONCLUSIONS

Premature infants crossed the recommended radiation threshold more often than term infants in the year after discharge from birth hospitalization.