FORT WORTH (CBSDFW.COM) – Despite battling a rare form of cancer since June of 2019, 13-year-old Joey Belles did something many dream of accomplishing. He walked a marathon.

Belles is the first Cook Children’s patient to walk 26 miles during treatment. Slowly at first, Belles walked around the Bone Marrow Transplant Unit everyday to reach his goal.

READ MORE: 'I'm Worried I'm Going To Kill My Parents' Man Told 911, Pointed Fake Gun At Fort Worth Police Before Being Killed

“When I first got here, I was sick and I was moving pretty slow,” said Joey. “We started walking the first day, but I could only do two laps.”

Now less sloth (Belles’ spirit animal), more determined tiger, the teen is an inspiration to all who meet him.

“For about a week, I did two to four laps a day and then I started getting to 10 and I thought ‘Wow, this is good!’ and then I started doing 20,” Belles said.

All smiles, Joey Belles crosses the finish line at Cook Children’s Hospital. (credit: Cook Children’s Hospital)

On July 3, Cook Children’s neurosurgeon Daniel Hansen, M.D. removed Joey’s tumor. Luckily, Dr. Hansen was able to get the entire mass at once. From there, Joey began a strict regimen of proton radiation therapy. In November, he was admitted to Cook Children’s Bone Marrow Transplant Unit to begin stem cell chemotherapy.

“It was really hard on his body,” Denise said. “You deplete them (patients) of everything and start from scratch. But the doctor said to Joey ‘You don’t have a shot if you don’t have the right attitude.’ So we came up with a plan and no matter what, we were going to be positive about it.”

Part of the plan came together after a visit with a physical therapist. She asked Joey to start walking and told him that if he kept track of his progress, he could win a gift card once he hit 10 miles. The incentive is part of a new program at Cook Children’s called ‘Miles in Motion’ which encourages hematology/oncology patients to get moving.

Physical therapist Lydia Robey was part of the team that came up with the idea for ‘Miles in Motion’ as part of a quality and safety initiative to motivate patients out of their beds and exercising.

“We were brainstorming how to increase activity for this particular group of patients and one of our dietitian pointed out that these kids were losing muscle mass at a far greater rate than they should,” said Robey. “Some of that was due to inactivity, as well as steroids and medications that cause muscle atrophy. We started reviewing the literature and the evidence just became overwhelming of how important exercise is.”

READ MORE: Dallas City Council Unanimously Approves Major Ethics Reforms

On Thursday, Feb. 20, Joey made his final laps around the unit were he walked for the past four months. This time, nurses, child life specialists and physical therapists lined the walls. They held up handmade signs and cheered him on. With just five laps to go, Joey took one step at a time, thanking his mom and dad for their support as they finished the journey together.

At the final lap, excitement built as the medical staff cheered his name. “Joey, Joey, Joey!” they chanted until breaking into a loud roar as Joey ran through the finish line, a paper streamer strung across the hallway.

He did it. Joey walked a marathon.

“It was awesome,” he said. “I could have never done it without my family, the whole team we have. Everyone has been so supportive of me. It’s just truly amazing what we have done, me and my parents.”

This wasn’t the first marathon completed by a member of the Belles family. Joey’s mother Denise ran the New York marathon in 2010, but she said this one was much better.

“This one is more rewarding,” Denise said. “His training was harder. I definitely feel more fulfilled with his than mine. It means so much more.”

If that wasn’t enough, finishing a marathon wasn’t Joey’s only major accomplishment of the day. It was also his final day of chemo.

“In the beginning, I really thought this was going to be devastating,” said Joey. “But everyone has been helping me and pushing me. With them, I knew I could get through this and do it with power.”

With his treatment coming to an end, Joey and his family are making plans for the future. They’re downsizing to a smaller home so they can take more trips together. This summer, they hope to go to Italy.

MORE NEWS: Harris County Jail, Texas' Largest, Under Renewed Scrutiny After Report Of Sexual Assault Of Sergeant