Excess radiation and organ dose in chest and abdominal CT due to CT acquisition beyond expected anatomical boundaries.

OBJECTIVES

To assess the extent of extra imaging beyond the prescribed anatomical margins for chest and abdominal CT and to determine associated extra patient and organ dose estimates.

METHODS

For 167 consecutive patients undergoing routine chest and/or abdominal examination with 128-slice CT, extra imaging length was evaluated on coronal images. Effective and organ doses (thyroid, liver, breasts, testes) were calculated. Paired t-test was applied to evaluate statistically significant differences between prescribed and actual imaging length, and associated doses.

RESULTS

133 (80%) examinations had extra coverage (mean 4.6 cm, range 1-19.5 cm). Significantly higher (P < 0.05) effective doses for chest CT (mean 4.8 mSv vs 4.2 mSv for actual vs prescribed volume of interest), abdominal CT (8.4 mSv vs 7.9 mSv) or thorax-abdominal CT (12.8 mSv vs 11.9 mSv) were found. A significantly higher (P < 0.001) organ dose was estimated for thyroid (extra dose 99% corresponding to 5.1 mSv), liver (56%, 2.2 mSv), testes (115%, 7.6 mSv), and breasts (163%, 1.5 mSv).

CONCLUSIONS

Imaging beyond anatomical limits during routine chest and abdominal CT results in higher organ and effective doses. Continuous training of the technologists remains important. Physicians and technologists must be kept aware of the additional dose associated with extra imaging.

KEY POINTS

Imaging beyond anatomical boundaries often occurs during chest and abdominal CT. Such imaging beyond anatomical boundaries leads to higher organ and effective doses. Physicians and technologists should be made more aware of this additional dose.