Yes over years, in that the amounts of radiation are high and cumulative. However, when I was first diagnosed, I lost count of the number of CT scans I had. The benefits must be weighed against the potential risks. Finally, at 5 years of remission, my dr is switching me to MRIs for my general scans, with CTs only if the extra information is needed. Chemo and radiation treatments are harmful, too, but are necessary evils in the fight against our cancers.
Yes, we are doing things to our bodies that in healthy bodies would be ill-advised. However, we are working against the very sinister evil of cancer, and therefore must take risks to have the benefits.