This is a textbook case of classic recall bias, where a study group with cancer, for example, remembers being exposed to something that the study is trying to link more so than a group without cancer.  Even the authors and the American Cancer Society admit this flaw, but yet it is throughout our news and forever linked in many people’s mind.  The radiation dose from 4 bitewings is 0.005 mSv which is less than one day of natural background radiation (0.008 mSv).  It would be equally valid to propose that people born in a leap year have increased cancer risk (not true, by the way).