President George W. Bush appointed Dole in 2007 to a panel investigating conditions at the hospital.
"I never really thought I wanted to spend that much time there," he joked at a 2011 appearance honoring the 50th anniversary of his being first elected to Congress.
Asked about the milestone of his 90th birthday, Dole said "It's going to be a special day. I don't know how many people reach 90," adding "I am kind of excited about it."
Many friends and old staff members will gather Tuesday for a party celebrating his special day.