Proton beam therapy for pediatric cancers

Dec. 18, 2024

In the realm of pediatric oncology, where every decision carries the weight of a young life's future, the advent of proton beam therapy emerged as a groundbreaking innovation for children with cancer. This innovation has allowed Mayo Clinic's Proton Beam Therapy Program to apply pencil beam scanning to deliver precise radiotherapy to tumors with lower doses of radiation to nearby healthy tissue. This highly targeted therapy is ideal for young people whose organs are still developing.

Precision targeting, reduced side effects

Compared with conventional radiation therapy, proton beam therapy allows reduction in radiation dose to healthy tissues and organs while delivering the required dose to the tumor. This ability can lead to fewer side effects while maintaining similar tumor control rates when comparing outcomes to X-ray-based radiation treatments. This translates to fewer children needing lifelong hormone replacement therapy and fertility treatments later in life.

"Within the last few years, there have been publications showing that kids have fewer pituitary problems and fewer thyroid problems," says Anita Mahajan, M.D., a radiation oncologist and medical director for the particle therapy center and chair of the pediatric disease group at Mayo Clinic Comprehensive Cancer Center in Rochester, Minnesota.

"There are an increasing number of reports with long-term follow-up data demonstrating that children receiving proton radiation for brain tumors, such as medulloblastoma, show less decline in their cognitive development," says Nadia N. Laack, M.D., a radiation oncologist and chair of Radiation Oncology at Mayo Clinic Children's Center in Rochester, Minnesota. "That contrasts with traditional radiotherapy, where we generally see a steady decline in development after treatment."

Reduced radiation toxicity can be achieved without compromising a patient's outcomes. For example, a September 2019 study published in the International Journal of Radiation Oncology, Biology, Physics found that the two-year survival rate for children with brain tumors treated with pencil beam scanning proton therapy at Mayo Clinic is 93%.

Mayo Clinic researchers continue to gather data from proton beam patients about side effects, tumor control, well-being and more. This extensive database is used to develop better delivery techniques and care models.

For example, the results of a pilot study evaluating the feasibility of memantine in reducing cognitive impairment in pediatric patients after radiation therapy for central nervous system tumors became the basis for a national clinical trial that is currently ongoing. In a study published in the November 2024 issue of the International Journal of Radiation Oncology, Biology, Physics, Mayo Clinic researchers found that memantine is a feasible, safe, and well-tolerated addition to multimodality treatment for pediatric CNS malignancies. Results from the national clinical trial will further define the value of memantine in the pediatric population.

Specialized care

Pediatric tumors can pose unique challenges and benefit from highly specialized expertise. Mayo Clinic's proton beam program incorporates advanced techniques, such as biological dose modeling to ensure each patient gets the exact amount of radiation needed and in-room image guidance for precision delivery. Adaptive planning, which allows radiation plan modification to adjust for changes in the tumor or patient during treatment when needed, also is used when indicated.

"We certainly don't want any extra burden on families and to make them travel for something that could be done closer to home," says Dr. Mahajan. "There are certain cases where there is a clear indication that proton therapy is going to be better for certain brain tumors such as medulloblastoma. However, having said that, children with Hodgkins disease, neuroblastoma in the abdomen, rhabdomyosarcoma anywhere in the body — often, there is a role for proton therapy."

When considering proton beam therapy, a referring physician can consult Mayo Clinic Children's Center at any time — whether a patient has a preliminary diagnosis or is currently undergoing treatment.

"If there is a patient that has a new diagnosis for rhabdomyosarcoma or mesoblastoma, it's ideal to hear about it as soon as possible," says Dr. Mahajan. "This helps us plan ahead for certain situations that might require more immediate radiation after surgery, for example. For other situations where radiation treatment happens several months down the road, we can talk about it at any time during the initial phases of chemotherapy."

Collaborative efforts

With a pediatric cancer diagnosis, second opinions can be crucial. "Oftentimes we can look at the patient with a fresh pair of eyes," says Dr. Mahajan. "We will take a fresh look at the imaging and review the pathology. Sometimes we identify things that weren't quite clear the first time around. There can be a different interpretation of the same tumor pieces."

The team at Mayo Clinic Children's Center has extensive experience in diagnosing and treating many types of cancer, including rare and complex forms. "A particular diagnosis might be considered one in a million to most," says Dr. Mahajan, "but it's certainly not one in a million here."

"We're able to incorporate all of the expertise that Mayo Clinic has in radiology, pathology, radiation, medical oncology and surgery, for example," says Dr. Mahajan. "All of this enhances our ability to deliver excellent care."

Collaboration extends to all members of a patient's care team. Oftentimes, a patient will need subsequent chemotherapy or systemic therapies, highlighting the importance of communication between Mayo Clinic Children's Center and a patient's local care team.

"When working with a patient's referring physician, we give updates during the course of treatment," says Dr. Mahajan. "For example, we can discuss their treatment plan overall, mention any new issues as they arise or reach out if something unexpected happens. And with the prevalence of video conferencing, many of our referring physicians are able to participate in weekly tumor board conversations about their patients."

"It's really important to have a sounding board for challenging cases," says Dr. Mahajan. "Oftentimes patients develop a sense of trust with us and with their physician groups closer to home, and patients really appreciate the special partnership that we develop."