Discussion
head injury
ADVERSE EFFECTS
In the largest study hitherto conducted on CT head examination in childhood and high school eligibility and grade scores at end of compulsory school and where radiation doses where randomly assigned, no statistically significant effects on high school eligibility or grades at the end of compulsory school were found. Furthermore, the more specific dose analyzes showed no statistically significant differences between the different dose categories and their proportions of high school eligible and higher scoring grade category.A total of 832 subjects, representing 93% of the original cohort, were examined in the present study. The main known reasons for loss to follow up were incomplete PIN and not yet having graduated, i.e. having no school grades for analysis. The exposed and unexposed groups did not show any statistically significant differences in the descriptive variables; proportion of male participants, age at head injury, age at graduation, time between head injury and graduation, GOSE-score at 3 months after head injury, or education level of mother. Single and multivariate analyses did not show any statistically significant differences between the exposed and unexposed groups for high school eligibility or grades at end of compulsory school. Likewise, the dose analyzes did not show any statistically significant differences between exposure groups.This study had the advantage of having radiation exposure randomized which is rare among studies of adverse effects of radiation. Other advantages were a high follow up rate, and inclusion of both males and females. Limitations of the study include the different follow up times, and that, even though the study is one of the larger of its kind, the sample size may have been too small to detect small variations between exposed and non-exposed. The small differences found were generally in favor of the unexposed, or of those exposed to lower doses of radiation compared to those exposed to higher doses, but neither of the results were statistically significant. Whether these differences had been statistically significant in a larger study cannot be told, but it is reassuring that any effect on school grades of computed tomography of the head is too small to be detected in a study of over 800 study subjects. Another limitation is that the present study measured only eligibility for high school attendance, and not actual high school attendance or completion. Like Blomstrand et al. [In conclusion, the exposure to a low ionizing radiation dose, such as from a CT examination, to the head in childhood is not associated with neither high school eligibility nor grades at end of compulsory school to such extent that it can be measured in a study of more than 800 study subjects, half of whom were randomly assigned to computed tomography.We acknowledge the OCTOPUS-group, especially Britt-Marie Hune and Carin Cavalli-Björkman for their support with accessing data and information from the OCTOPUS-study. Furthermore, we acknowledge Henrik R Andersson for helping us getting started with the radiation dose reconstructions.