Evans, an avid runner, said he's canceled his plans to run the 2016 edition of the race on April 18 so he can tend to security duties. He said he had planned to make it his 50th marathon and 19th Boston, but Tuesday's attacks in Brussels prompted him to reconsider.
Instead, he said, marathon security will be his main focus.
"I can't in my right mind go out and lace up the sneakers and run that day," he said in his office, where dozens of marathon medals decorate the walls. "We're only 3Â½ weeks away. My priority is here, doing my job and making sure the race goes off without any problems."