A bicyclist was treated for serious injuries Monday after he was struck by the driver of a box truck in Deer Park, police said.

The truck was traveling south on Commack Road in Deer Park and attempted to make a right turn onto westbound Marcus Boulevard around 2:10 p.m. The bicyclist, Vincent Kelleher, 56, who police said is homeless, was heading south on Commack Road when he was struck.

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A Suffolk County police helicopter airlifted Kelleher to Stony Brook University Hospital. The driver of the truck, Mark Santucci, 51, of St. James was not injured and remained at the scene.

The Deer Park Fire Department also responded to the crash.