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MRI and PET Scans, and Cumulative Radiation Exposure

Re: previous MRI, my neurosurgeon wrote, "The follow-up brain scan... was reviewed at our Gamma Knife Conference... The scan presented was stable. We recommend a follow up MRI brain without and with contrast in three months."

Re: latest PET scan, it did not raise any areas of concern. The interval on future PET scans for me may be adjusted slightly upwards.

Are there cumulative exposure risks from the radioactive dyes and CT portions of PET scans? The conventional view is that there is a linear relationship between any radiation exposure and the risks of DNA damage. I learned of a contrasting theory, Radiation Hormesis, the idea that small doses of radiation could actually be stimulating to and strengthen the body's DNA repair system. However per the article above,
"At this time, the assumption that any stimulatory hormetic effects from low doses of ionizing radiation will have a significant health benefit to humans that exceeds potential detrimental effects from radiation exposure at the same dose is unwarranted." 
The article does mention a proposal to build an ultra-low-level radiation lab, to test animals in an environment with almost zero radiation to see if there is any merit to the theory. Meanwhile, it's a way for patients and radiation workers not to worry too much about PET scan radiation.
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