Proton therapy, which uses high-energy subatomic particles, may offer a precise, organ-sparing treatment option for children with high-risk forms of neuroblastoma, the most common solid tumor of early childhood. For patients in a new study of advanced radiation treatment, proton therapy spared the liver and kidneys from unwanted radiation, while zeroing in on its target.
Protons are the positively charged particles in an atom’s nucleus, and are used in therapy to destroy DNA in tumors and prevent cancer cells from multiplying. In children, this therapy is often used against spinal tumors. CHOP has recently been directing protons at neuroblastoma, long a special focus of the Hospital’s clinical and research programs.
Pediatric oncologists have an arsenal of weapons against neuroblastoma, but high-risk forms of this cancer present a particular challenge, often frustrating conventional treatment from the start or recurring in a resistant form.
The study included 13 children who responded well to initial chemotherapy, followed by surgery, more chemotherapy, bone marrow transplant, and, in some cases, immunotherapy. The advanced radiation treatment aimed to destroy remaining microscopic areas of cancer cells while minimizing toxicity to healthy tissue.
“As survival rates improve for children with neuroblastoma, we need to reduce treatment-related long-term toxicities,” said study leader Christine Hill-Kayser, MD, a radiation oncologist in The Children’s Hospital of Philadelphia’s (CHOP) Cancer Center. “Proton beam therapy offers precise targeting with less radiation exposure to healthy tissue.”
In planning radiation treatment for each child, the study team determined that 11 patients should receive proton therapy. The two other patients received intensity-modulated X-ray therapy (IMXT) because of the specific anatomy and location of their tumors. In IMXT, radiologists sculpt the radiation emitted from 7 different angles to modify radiation dosages in and around the targeted area.
None of the 13 patients had local disease recurrence or acute organ toxicity. For 11 of them, proton therapy provided the best combination of target coverage and organ sparing. “Protons are heavier than the particles in X-rays and have more stopping power,” said Dr. Hill-Kayser. “They deposit 90 percent of their energy precisely at the tumor site, with nearly zero radiation away from the tumor. That protects healthy organs—which, as growing tissues, are especially vulnerable to radiation damage in young children.”
The fact that individual characteristics made IMXT preferable to proton therapy in two children, said Dr. Hill-Kayser, underscores the need to meticulously customize radiation treatment to each patient. Overall, the current study shows that proton therapy should be considered for children with high-risk neuroblastoma. She added, “To better assess the use of proton therapy against high-risk neuroblastoma, we’ll need to study larger numbers of patients and do long-term follow-up. However, this represents a great start.”
Owing to collaboration between Children’s Hospital and radiation oncologists at Penn Medicine, the Roberts Proton Therapy Center, where the study was conducted, is the first proton therapy facility in the U.S. conceived with pediatric patients in mind from the earliest planning stages.
Dr. Hill-Kayser and colleagues published their study online June 4, 2013, in the journal Pediatric Blood & Cancer. More details on the study are available here.