The publication you cited said,

"Estimated lifetime cancer mortality risks attributable to the radiation exposure from a CT in a 1-year-old are 0.18% (abdominal) and 0.07% (head)-an order of magnitude higher than for adults-although those figures still represent a small increase in cancer mortality over the natural background rate."

"... the risk-benefit balance is still strongly tilted toward benefit, because the frequency of pediatric CT examinations is rapidly increasing, estimates that quantitative lifetime radiation risks for children undergoing CT are not negligible may stimulate more active reduction of CT exposure settings in pediatric patients."

"... 600,000 abdominal and head CT examinations annually performed in children under the age of 15 years, a rough estimate is that 500 of these individuals might ultimately die from cancer attributable to the CT radiation."

The key message is 'the risk-benefit balance is still strongly tilted toward benefit." The other messages are alarmist, superfluous, and contrary to the risk analysis. The authors are applying the risk model well beyond its validity and then applying the result to a large population in order to produce a large number of hypothetical deaths.

The authors claim that 600,000 CT exams to 1-year-olds might ultimately lead to 500 deaths. The authors fail to acknowledge that the expected cancer deaths for 600,000 persons is 180,000 with an uncertainty of 27,000. The 500 alleged CT deaths is less than 10% of the standard deviation of the expected deaths.

The calculated risk to a single individual is negligible. It is still negligible for each of the 600,000. The risk does not accumulate to 500 of the 600,000. Applying a risk that is less than 10% of the standard deviation of the background risk for 600,000 individuals does not change the background risk.

The risk model is not validated for the CT dose level. The uncertainty in the risk model at the CT dose level is much, much larger than the purported, negligible risk.

The timing is usually up to the discretion of the medical practitioner. He or she operates under the ALARA (as low as reasonably achievable) principle. As such as much radiation as medically necessary to achieve diagnosis (or in other cases treatment) is acceptable or in simple words at all times the minimum amount of radiation that can be used to achieve medical aim should be used. Modern units are also equipped with good dose reduction software's. So no I cannot say to you 30 seconds or 1 minute or 5 minute. Depending also on the ability of the CT unit being used, some may take a longer time to record the necessary slices as well (speed of unit).

Pediatric patients are of course more sensitive to the radiation than adults, therefore risk for them is also higher. However the amount of radiation dose depends not only on the scanning time, but also on other exposure parameters such as: tube voltage, current etc. Regarding the time of the examination, you can reduce it by using 2 different factors: Gantry rotation time and speed of the scanner along z-axis. The first one is limited by the manufacturer and it is usually from1.0 to 0.5 seconds per 360°. If you want to decrease the dose choose the lowest possible rotation time. The second factor can be adjusted by using pitch: as higher pitch as lower dose. However in this case you have to be aware to keep relatively good image quality and not to loose the diagnostic information.

@Natalie,

you forgot the special filtration, algorithms to suppress or diminuish signal noise. The rotation time doesn´t help, if you match the beam current to keep the signal noise ratio constant. Changing the pitch factor to higher values is able to diminuish the patient´s dose, but you loose details resolution.

And dear Joseph,

the central point with the calculators of produced additional cancer patients is the fact, that all these authors totally forget that CT examination can help to survive or to live in a better life quality. There is a well known principle: "Do more good than harm". 

@Hanno

Dear Hanno! Thank you for the additional information. As far as I know not all scanners use this algorithm ( keep the signal/noise ratio constant), it depends on the CT vendor.  And of course we did not forget about the main purpose of CT to provide reasonable image quality, that was mentioned  above.

Best regards, Natalia

The International Commission on Radiological Protection (ICRP) judges that life time cancer risk following exposure in early childhood is at most about three times that following exposure of the population as a whole.

The childhood radiosensitivity to cancer depends on organs/tissues, such that the Scientific Annex II of the UNSCEAR 2013 Report Volume II concludes that (1) children are more radiosensitive than adults for about 25% of tumor types (e.g., leukemia, thyroid, skin, breast and brain cancer), appear to have similar radiosensitivity to adults for 15% of tumor types (e.g., bladder cancer), and to be less radiosensitive than adults for 10% of tumor types (e.g., lung cancer), (2) The data are too weak to draw a conclusion regarding differences in risk with age at exposure for about 20% of tumor types (e.g., esophageal cancer), and (3) there is only weak or no relationship between radiation exposure and risk at any age of exposure for about 30% of tumor types (e.g., Hodgkin’s lymphoma, prostate, rectum and uterus cancer).

http://www.unscear.org/docs/publications/2013/UNSCEAR_2013_Report_Vol.II.pdf

I am not sure if there is a scientific consensus with a series of convincing epidemiological evidence that pediatric CT exposures increase cancer risk.

Example discussions are provided below for two large CT studies.

1) https://www.ncbi.nlm.nih.gov/pubmed/22681860

Exclusion of study subjects with predisposing conditions or suspicion of prior cancer derived from comparable medical sources, and additional exclusions of based on the full radiologist and pathology reports reduced ERR/Gy from 36 (95% CI: 5, 120) to 20 (–11, 86) for leukemia and from 23 (1, 49) to 10 (2, 26) for brain tumors. The reductions would have likely been larger. For more discussions, please see https://www.ncbi.nlm.nih.gov/pubmed/26882064 .

2) https://www.ncbi.nlm.nih.gov/pubmed/23694687

An increased brain cancer risk after abdominal/pelvic and extremity CT scans was reported, but the brain dose should be negligible. An increased risk of Hodgkin’s lymphoma and melanoma was reported, but these have not been associated with radiation. Breast is radiosensitive, but no increased breast cancer risk was reported. Increased cancers were reported in one to four years after exposure, but this implies no latency period. For more discussions, please see http://www.bmj.com/content/346/bmj.f2360/rr/648506 and https://www.ncbi.nlm.nih.gov/pubmed/25816281 .