LEWISTON — Among celebrities who raise money for charities, Patrick Dempsey is one of the best, marketing experts say.

The TV and movie actor’s personal connection to his cause and his continued involvement is worth a fortune, said John Mahon, a professor of management at the University of Maine and a private consultant.

“You can almost put celebrities on a scale,” said Mahon, who specializes on issues of branding and reputation. “Are they from the local community or not, yes or no? If it’s a yes, the potential to raise more money is increased substantially.”

Other factors include whether the celebrity’s fame is based on something past or current, if their fame was for something beloved and if they’re willing to appear publicly.

Dempsey, who was born in Lewiston and grew up in Buckfield and Turner, seems like a perfect case, Mahon said.

Inspired by his mother’s multiple diagnoses with cancer and the effects on the family, Dempsey created his namesake charity, the Patrick Dempsey Center for Cancer Hope & Healing, to offer services to people touched by cancer. His sister, Mary Dempsey, serves as the center’s assistant director.

Since 2008, the center has offered its services without charge, thanks to fundraisers including the annual walking, running and cycling Dempsey Challenge.

This year’s challenge is scheduled for Oct. 12 and 13. The “Grey’s Anatomy” actor is scheduled to attend every day and to cycle a 50-mile course, said Mark Turcotte, spokesman for the Dempsey Center.

“There are many a celebrity event where a name is attached, but a celebrity sighting is like sighting a white buffalo,” Mahon said. “They give their name willingly, and that’s good, and they might do a YouTube message or a video message or an audio phone call that can be used for it. But they’re not there.”

Turcotte said Dempsey remains committed to the center and the challenge.

“He’s as committed to this event today as he was on day one,” Turcotte said.

Each year has seen donations climb. In 2012, for the fourth annual challenge, participants raised about $1.2 million. All of it goes to the center.

“You can see the impact that it has,” Mahon said. “Everybody sees Patrick Dempsey, and I mean this with great respect, as a local guy coming home to contribute to his community. And because he’s doing it, and giving up his time and his sister’s involved, people are willing to give.”

Mona Elyafa, who operates a PR film in Los Angeles that represents several national charities, agreed with Mahon that Dempsey makes a strong spokesman for a charity.

And though Dempsey’s star power may have lessened a little as his show’s ratings have dipped (the show’s season 10 premiere drew a still-massive 9.1 million viewers), he remains able to draw lots of attention from corporate sponsors, said Elyafa, who also represents several celebrities and writes a Hollywood column for the Huffington Post.

“It would be fairly easy for (Dempsey’s) marketing team and PR to get exposure and advertisers to his cause,” she said. “They know that they’re going to get exposure.”

She added, “Any time you produce a charity event and you have big names attached to it, it’s fairly easy to get sponsors (and) advertisers because they know they’ll sorta get their money back.”

Mahon declined to attach a dollar value to what Dempsey’s involvement might mean, but it’s a lot, he said.

“It is probably worth anywhere from a 50 percent to a 100 percent increase in donations,” he said.

dhartill@sunjournal.com