The music wafted out of the ballroom and down the hallway as the prom-goers broke away for portraits against a printed backdrop of a medieval castle.

There had been the traditional couples pose — the boys in suits, the girls in gowns. And then a group picture. Then came the picture of just the girls, and then the one of just the boys.

Then individual shots — and finally it was Mark Acosta's turn. He struggled to stand unaided.

Before, with the others posing with him, it had been easy to hide the machine providing the fluids his body needed after a round of chemotherapy earlier in the day.

Now, as he rose alone, a nurse pushed it off to the side. Then she crouched behind him, out of the picture, grabbing his waist with both hands to help support him.

The look on his face revealed his mixed feelings, feelings he wouldn't talk about out loud with his friends. Not now anyway.

The 16-year-old had had different plans for this special night out. He had planned to bring a date. He had intended to dance. He would, of course, be walking unaided...

But cancer has a way of upsetting the best-laid plans.

Waiting off to the side, in a line, were dozens of other teens: A boy with a cane, another in a wheelchair; a girl wearing a wig, another attached to the same kind of machine that Acosta had.

Most in this room had either missed or been forced to alter teenage rituals: learning to drive, making plans to go away to college — and, of course, going to the prom, that dance that for so many marks the entrance into adulthood.

This is prom's promise to the young.

At this dance at the Children's Hospital of Orange County, though, there was another kind of promise — for one night at least, the promise of normalcy.

Red and Gold Wheelchairs

Pink's "Get the Party Started" had already kicked off the dance by the time Acosta left his hospital room.

The nurses surprised him and another teen in the ward with wheelchairs decorated with red and gold ribbon and the red construction paper cut-out of the fleur de lis, a stylized version of the flower often associated with medieval French monarchy.

Acosta had wanted to walk to the dance. He didn't like to use the wheelchair. But his battle with cancer had caused "foot drop," a weakness or paralysis.

"He struggles with the possibility of not walking," John de la Rocha says of his son. "He said, 'I can go through this. I can go through all of this, but I want to be able to walk.'"

He has had two years of treatment. He was 14, and his family was moving into their new home in Whittier the day the headaches he had been suffering became unbearable. Rather than hang pictures and unpack boxes in their new home, his parents took him to the hospital.

The diagnosis: medulla blastoma, an aggressive, malignant brain tumor.

Doctors told his parents, Anita and John de la Rocha, that the tumor had probably been growing in his brain since he was 12. After surgery and chemotherapy treatments, Acosta went into remission in March 2006.

Since then, he was learning to walk again. He was getting better. He was back in school, hanging out with friends.

And he was making plans to go to the hospital's prom, an annual event for high school-aged patients, many of whom are unable or unwilling because of their appearance to go to their own school prom.

But as the date approached, an MRI gave the family news they had prayed would never come: The cancer was back. It had recurred in his spine.

A week later, Acosta underwent surgery to remove the tumor. And a week after that, days before the June 30 prom, he began his first round of what will be nine months of chemotherapy treatments.

No Parents Allowed

Away from the children's cancer unit, a conference room had been turned into a magical castle on the theme "A Medieval Knight." The hallway was decorated to resemble a drawbridge, and there were plants, a plastic grass carpet and a life-size plastic horse adorned with chain mail.

Greeting the prom-goers were actors from the "Medieval Times" dinner and tournament show in Buena Park. In full costume, a king, knights and a princess welcomed them.

Patients 15 and older were allowed to invite dates and friends. Parents could bring their son or daughter and take a look around, but then they had to leave. Why? Normalcy again. Parents don't go to the high school prom either.

"That's a hard one for some parents. I've had a couple get angry with me when I tell them they can't come," says Mitzi Bennett, a clinical social worker who organizes the prom. "You know they go through this together, and they share everything. So they often want to share this with their child, too."

Acosta is wheeled through the drawbridge entrance by his oldest sister, Ashley, 18, and his cousins, Victoria Ferreiro, 14, and Matt Ferreiro, 17, who pushes the pole attached to the machine that administers fluids. His parents and 11-year-old sister Kristen watch, smiling.

It's as it should be — proud parents looking on as their son, dressed in a new dark suit, goes off to a dance.

They have a night free, too, a rare chance for dinner with friends. They joke they have forgotten what that's like.

"We haven't decided where to go yet," Anita de la Rocha says, laughing.

Just One Dance?

The DJ is spinning Sean Paul's "Break it off," and Acosta wants to dance, just one dance.

His friend, Josh Mack, has already been on the dance floor several times. Mack, 17, and Acosta met at the hospital last year when Mack was fighting cancer that eventually took his leg.

The two have formed, along with another young man, their own clique of sorts, teen boys brought together by cancer but whose interests trend to normal stuff: music, jokes and, well, girls. They've even given each other nicknames. There's Marky Mark Acosta, J. Mac and Razzle Dazzle.

The friends and his sister see to it that Acosta makes it to the dance floor, maneuvering his fluids machine. Couples dance all around.

Ben Penman, 23, watches from the DJ booth. He doesn't know most of these teens. But he knows their story. Five years ago, he was treated for cancer in this same hospital. His first set of DJ equipment even came from the Make-A-Wish Foundation.

"I pretty much missed everything my junior year," he says. "I couldn't go to any dances, go hang out with my friends."

So when Children's Hospital started holding the prom a few years ago, he volunteered to spin tunes, knowing what a dance would mean.

'So Much Fun'

It's almost 10 p.m., and Acosta has to call it a night. He's fatigued and his stomach is upset — chemotherapy side-effects.

As his sister wheels him back to his room, he wonders aloud if he can just rest for a few minutes and return before the dance ends.

Possibly, his sister soothes.

In his room his mother is waiting. She asks about his night. Over the past few months, he has been dictating his observations, experiences and thoughts to her to write down with the hope of one day writing a book about his cancer battle.

There are no books out there, he says, that talk about what it's like to be a teenage boy with his kind of cancer.

"I had so much fun," he tells her as he lies down. "Nobody stared at me. Nobody asked any questions."