STATE COLLEGE — Kirsten Quisenberry offered a simple reason why Penn State students spend an entire year preparing for their annual dance marathon in support of sick children.

“Cancer doesn’t stop, so we don’t stop,” she said in a new Penn State Public Broadcasting documentary about Thon.

Quisenberry, the 2012 Penn State IFC/Panhellenic Dance Marathon public relations chairwoman, was among the dozens of students interviewed in “Why We Dance: The story of Thon” by filmmakers Cole Cullen and Jeff Hughes. Their hour-long work chronicles the 2012 Thon and the year leading up to it, weaving together accounts from student volunteers and the families of children battling pediatric cancer.

Since its start 40 years ago, Thon has become one of Penn State’s celebrated traditions. Hundreds of students dance for 46 hours in the Bryce Jordan Center.

With more than 15,000 students involved, Thon bills itself as the largest student-run philanthropy in the world. Last year’s event raised a record $10.6 million.

Friday at the State Theatre, selected community residents and past and present Thon volunteers attended two advance screenings. WPSU-TV and public television stations in Erie and Wilkes-Barre/Scranton will broadcast the film at 8 p.m. Thursday. The premiere will air on Pittsburgh and Erie stations an hour later.

At the screenings, audiences got an emotional look at the work behind Thon — from “canning” on streets to raise money to visits with adopted Thon families at their homes to the logistics of transforming the BJC into a giant dance club.

“Our goal for the show was for people to have a real understanding of why people are so passionate about Thon, and to understand that it’s more than two days in February,” Hughes said.

In all, the filmmakers shot about 110 hours of footage. The final result captured more than 80 interviews and many rare glimpses, including one of the overall Thon chairwoman and four other leaders, alone with a laptop, tallying the total donation amount — a climactic scene most Thon volunteers have never witnessed.

“A lot of people who have seen the show, they say it’s their favorite moment,” Cullen said.

Though they needed time to win the full trust of Thon students, the featured Thon families — including the family of Philipsburg’s Emily Whitehead — opened up immediately, the filmmakers said.

“All they wanted to do was give back to Thon,” Cullen said.

Also depicted in the film are charitable efforts inspired by Thon. In 2006, a father whose son recovered from cancer showed his gratitude to Thon by organizing the Hope Express, a 135-mile relay run from Hershey to deliver letters to Thon dancers.

And since the 1990s, schools locally and statewide have been staging mini-Thons. Last year, 82 events raised more than $1 million for the Four Diamonds Fund, which supports for cancer- stricken children and their families at Penn State’s Hershey Medical Center.

One thing omitted was any mention of the Jerry Sandusky child abuse scandal that rocked Penn State in late 2011 and over the winter. Hughes said he wrestled with what to do.

“I ended up deciding it would take away from (the students’ and families’) story,” Hughes said. “It was probably one of the hardest decisions we had to make, but I think we made the right decision.”

Lynn Koehler Yingling, of Altoona, thought the film hit all the right notes.

A Thon moraler from 1992- 1996, she attended the first Friday screening and thought it was “amazing.”

“Everything just flooded back,” she said.

She said the film caught the true spirit of Thon, that “there’s so much more” than just the event itself.

“It made me remember why I did it,” she said.

Chris Rosenblum can be reached at 231-4620. Follow him on Twitter @CRosenblumNews