When citing the work of the same author multiple times in one paragraph, you do not need to reference the author at the end of each sentence. That would look clunky and make your writing stilted. Instead, introduce the author with a full in-text citation at the beginning of the paragraph and then, again, at the end. For the body of the paragraph, you can refer to the author by name or pronoun.
Example:
According to Spitzer's (2010) study the effects of radiation on humans presents...Spitzer's study developed the guidelines needed to test...The most important find in his study was that....Spitzer concluded the benefit of radiation...The evidence that proves these guidelines work (Spitzer, 2010).