Nancy J. Tarbell, MD
Pediatric Radiation Oncology
Yawkey Center for Outpatient Care, Francis H. Burr Proton Therapy Center
Phone: 617-724-1836
“Isn’t she beautiful?” marvels Dr. Tarbell, chief of Radiation Oncology at MassGeneral Hospital for Children as she admires a photo of two-year-old Mary Conroy from Marshfield, Massachusetts, who has successfully finished treatment for a brain tumor called ependymoma at MassGeneral Hospital for Children. “It’s wonderful to see how far she has come when you think about what she has been through. And that’s really the heart and soul of our story.”
At age two Mary developed flu-like symptoms; then began walking unsteadily and vomiting. She was diagnosed with anaplastic ependymoma in the posterior fossa, a type of brain tumor that accounts for ten percent of all pediatric brain tumors. The good news was that it had not metastasized. Fearing long-term side effects from conventional or photon-based radiation therapy, specialists at MassGeneral Hospital for Children decided that Mary was a perfect candidate for proton radiation therapy, exclusively offered here at the Frances H. Burr Proton Therapy Center on the Massachusetts General Hospital campus. Doctors quickly went to work with an aggressive and integrated team approach that included surgery, followed by radiation therapy using protons. This restored Mary’s young life back to health. Today she’s a healthy three-year-old, learning new words and loving life.
Mary is one of hundreds of children each year under the pioneering and expert care of MassGeneral Hospital for Children pediatric cancer specialists, Dr. Tarbell and the Department of Radiation Oncology, and the Frances H. Burr Proton Therapy Center. They are delivering a new generation of hope to pediatric patients with tumors and soft tissue sarcomas through proton based high precision radiation therapy.
The benefits of proton therapy
Protons are positively charged subatomic nucleic particles. The protons are accelerated to near the speed of light by a cyclotron, creating a beam that can be directed at tumors. Depending on the size, location and other critical dimensions of a tumor or abnormal tissue, specialists at MassGeneral Hospital for Children are able to target the proton beam at the tumor. A burst of radiation energy is released at the point of greatest penetration in the abnormal tissue, known as the Bragg Peak. Because protons have a defined range, they have no exit dose, sparing normal surrounding tissue. This is a breakthrough in radiation treatment, because conventional gamma or X-ray beams used in radiation therapy travel beyond the tumor and thus radiate healthy surrounding tissue. This results in deleterious side effects, such as developmental delay, risk of secondary tumor, potential hearing loss, and other effects on the bone and developing brain in pediatric patients. Proton therapy is indicated for irregular shaped lesions such as medulloblastoma and soft tissue (muscle and other connective tissue) tumors in children that arise near critical normal structures. These include the brain, eyes, ears, and the spinal cord, which can be more effectively spared adverse radiation effects with the proton beam.
“We can do things we never dreamed about before,” says Dr. Tarbell. “With conventional radiation therapy, there can be damage on the way in and on the way out when you’re using radiation to treat tumors because of the energy scatter,” she says. “It’s not a good thing to radiate healthy brain tissue, but with proton therapy, because there’s no exit dose, the normal brain receives far less radiation and that’s tremendously exciting,” she says. While there is an entrance dose, it’s still far less than with conventional radiation therapy.
Its benefits in the pediatric population are significant, considering healthy developing bone and tissue are adversely affected with traditional radiation. “Developing bones and tissue in the pediatric population are sensitive. If you radiate the growth plate of bone in a child, you could be stopping its growth. The potential asymmetry and risk of orthopedic problems is substantial,” says Dr. Tarbell. “With proton therapy we’re very excited because we can target tumors near critical structures and not affect them.” With conformal proton therapy, the dose of radiation is targeted directly to the tumor, thereby minimizing long-term side effects. Three types of proton-based radiation therapy exist at the Frances H. Burr Proton Therapy Center: Proton Radiotherapy for lesions in the body, Proton Stereotactic Radiosurgery and Radiotherapy for lesions in the brain, and Proton Ocular Radiotherapy for lesions in the eye.
Proton therapy is a terrific breakthrough in radiation therapy to target non-metastatic, localized cancers like soft tissue sarcomas and many pediatric brain tumors. One common pediatric brain tumor, medulloblastoma, is currently being studied through funding from the National Institutes of Health.
A legacy of innovation
The use of protons in the scientific realm gained momentum about forty years ago in nuclear physics, primarily to study the basic components of nuclear matter and its reactions to inform national security and intelligence issues. Exploratory work with protons also began during this era in medical imaging, diagnostic tools and radiation therapy. The Harvard Cyclotron Laboratory was one of the world’s first facilities to explore this utility in the 1960s. At that time, Massachusetts General Hospital neurosurgeons William Sweet, MD, and Raymond Kjellberg, MD, used proton beam therapy with much success in obliterating benign tumors of the pituitary gland and arteriovenous malformations in the brain. However, the extraordinary advancement soon revealed its limitations in medicine. The cyclotron had limited power and a fixed position so it couldn’t rotate around patients. These factors diminished its effectiveness to directly release energy to targeted tumors, particularly deep in the body.
Former Massachusetts General Hospital Chief of Radiation Oncology Herman Suit, MD, PhD, knew that an investment in this remarkable technology needed refinement but would produce a return many times over through the transformation of lives, especially young ones, whose growing bodies would be at risk with conventional radiation therapy. Dr. Suit engineered the vision to build the $52 million Frances H. Burr Proton Therapy Center on the hospital campus. The facility, which became operational in 2001, was built with funding in part from the National Cancer Institute. With this new facility in mind, Dr. Tarbell was recruited from Boston Children’s Hospital to help design and build the pediatric radiation oncology program. This phenomenal approach to radiation therapy is currently only available here and at Loma Linda University.
Specialists here agree that the benefits for patients like Mary are just beginning to unfold, as proton therapy is poised for use in the future for other kinds of cancers. But for now, seeing the gleam in Mary’s eye is a proud and happy moment for Dr. Tarbell as she watches her grow and her own life story begins to unfold.
Nancy J. Tarbell, MD, is the CC Wang Professor of Radiation Oncology at Harvard Medical School and chief of Pediatric Radiation Oncology at MassGeneral Hospital for Children. Dr. Tarbell is an internationally recognized expert in pediatric radiation oncology and pioneered the application of stereotactic radiation therapy for pediatric brain tumors. Consistently listed in The Best Doctors of America (Woodward and White), Dr. Tarbell serves on the national Children’s Oncology Group Brain Tumor Committee and chairs the Radiation Oncology Committee of the Pediatric Brain Tumor Consortium. She is a member of the prestigious Institute of Medicine of the National Academies and has authored more than two hundred original publications and chapters. Dr. Tarbell is an editor and an author of Pediatric Radiation Oncology, now in its 4th edition.
For more information about pediatric radiation oncology at MassGeneral Hospital for Children, please call 617-724-1836.
