We don't really know. Data that show X dose of radiation increases the probability of developing cancer by Y% is based on studies on survivors of atomic blasts. The number of people exposed to an amount of radiation equivalent to a handful of CT scans is pretty small relative to the effect size that's claimed, so there is reason to be skeptical.
See https://www.scientificamerican.com/article/how-much-ct-scans... for a jumping off point into this type of research.