Eleven-year-old Brendan Sanchez lost a leg to bone cancer. He still undergoes chemotherapy and feels pain from the missing limb.
"It's trying to find its way back home and sometimes it hurts," he says, "kind of like someone poking you and poking you and poking you."
To relieve his pain, he undergoes a technique that is strikingly simple and possibly as old as humanity.
"Let your imagination wander as you start to see that waterfall," says his specialist Dr. Mark Popenhagen, a psychologist at Denver Children's Hospital.
Visualization and relaxation is just starting to be used widely for children like Sanchez.
"It takes a few pills away, because you don't really need that many pain pills," says Sanchez. "It actually helps quite a lot."
Popenhagen teaches Sanchez the techniques in the hospital, but he can use them anywhere.
"He pretty much tells you to go somewhere you'd like to be," says Sanchez.
He says it often works and his mom, Judith, agrees.
"It gives him more control, and it makes him feel good that he has something that's not a pill," she says. "He can use it in the car on the way home from the hospital, or to the hospital, or when he wakes up at 3 a.m. with a phantom leg pain."
How does Popenhagen deal each day with children in pain?
"What everybody thinks is that it's all terrible and you hear kids screaming all day long, and that's not it," he says. "You live for the moments where they run up and wrap their arms around you and say thanks."
Brendan Sanchez is certainly one of those grateful ones.
"It just make me feel better," he says.