Q&A: Proton therapy for pediatric patients

Anita Mahajan, M.D., associate professor in Radiation Oncology, answers questions about proton therapy for pediatric cancer patients.

What is proton therapy?

Proton therapy is an advanced form of radiation therapy that uses protons, which are charged particles from an atom. The advantage of proton therapy over traditional forms of radiation treatment is its ability to deliver a pencil-thin beam of radiation to the tumor area with remarkable precision -- within one millimeter -- that avoids the surrounding tissue, generates fewer side effects and improves tumor control.

Proton therapy requires a highly specialized machine to deliver treatment, as well as a highly trained staff to ensure the best planning and treatment.

How does it differ from traditional (photon) therapy?

Proton therapy is different from traditional X-ray or photon therapy because it aims high-energy protons very accurately at the area of concern. Once protons enter the body, they deposit their energy (dose) at a precise location and stop, allowing no dose of radiation to go farther into the body. With more common radiation treatments that use X-rays (also known as photons or gamma rays), radiation is aimed precisely at the tumor. However, some radiation continues through the body, radiating organs and tissues that may not require treatment. This dose is called the "exit dose" and is almost non-existent with proton therapy.

What are its advantages?

The biggest advantage of proton therapy for children is that it reduces the dose to the body outside of the tumor area. In addition, there tends to be less radiation deposited between the entry point on the surface of the patient's body to the target area, know as the "entrance dose." Proton therapy may allow more aggressive treatment of tumors near or within sensitive organs, such as the lungs. In children, there may be a reduction in side effects with proton therapy. There's convincing evidence that even low doses of traditional radiation can increase the risk of secondary tumors.

Why was it a good choice for Jake's rhabdomyosarcoma?

Jake had a relatively rare cancer of the soft tissue that originated in the skeletal muscle. He was an ideal candidate for proton therapy because he had a fairly large pelvic tumor, surrounded by sensitive organs, including the bowel, pelvic bone, femurs and testis.

We recommended proton therapy because we felt there would be an advantage with the reduction of dose to the intestines, pelvic bone and femurs. This dose reduction allowed less bone marrow suppression, less bowel irritation (which can cause diarrhea), and better nutrition and tolerance of chemotherapy. In addition, by lowering the dose to these areas, we hope that he has fewer side effects as he gets older.

Is proton therapy recommended for other pediatric cancers?

Proton therapy has been used for several different pediatric cancers, including brain tumors, sarcoma and lymphoma. It can and should be considered for any child who's receiving aggressive curative treatment where moderate to high doses of radiation are required.

Are there special considerations when working with pediatric patients?

Young children and some older patients require daily sedation to help them stay still for any radiation. Reliable anesthesia support is absolutely necessary to allow safe and efficient radiation delivery.

Treating children with radiation is very challenging and rewarding. We've made great strides in curing many more childhood cancers, but we also realize that these young patients have many side effects as they grow older from the therapies that have helped cure their cancers. When treating children, we realize that they require aggressive therapy including surgery, chemotherapy and radiation therapy. We have to be aware of their previous and ongoing therapies, and we must consider their age, growth potential and functional development to minimize side effects and maximize their future quality of life.   

What else should parents know about this therapy?

Proton radiation is an exciting technology that may help reduce side effects during and after therapy. It should be part of a multidisciplinary approach that's common for many childhood malignancies. So far, results indicate that the rate of successful treatments is identical to traditional radiation, with a potential added benefit of fewer side effects.  Proton therapy also requires daily sessions (five days a week) for up to six weeks, depending on the particular tumor type. Patients may still have side effects, in particular from the organs and tissues adjacent to the tumor since part of them will receive most, if not the full, dose of radiation.