Using a Beam of Protons to Treat Lymphoma

Protons and Newer Techniques to Deliver Radiation Precisely

185304395.jpg

Radiation therapy is important in treating many different types of cancer. A variety of different forms of radiation are used to try to target malignant cells and tissues. Most commonly, photons (x-rays) are used in a technique called external beam radiation therapy, or EBRT.

There are a variety of newer radiation therapy techniques, however. Some of them have shown promise in more effectively targeting the cancerous tissue while sparing surrounding structures.

Proton Beam Therapy (PBT) Is Among Several Newer Techniques

Here are some of the techniques, or modalities, being used and discussed in the literature as potentially applicable to various types of cancer.

  • PBT refers to proton beam therapy.
  • 3D conformal EBRT refers to the involvement of computerized imaging analysis to plan the delivery of the dose of radiation more precisely to its target.
  • IMRT stands for intensity modulated radiation therapy, and this is another technique designed to destroy cancerous tissue but spare the surrounding tissue.
  • IGRT stands for image-guided radiation therapy, and it involves using imaging scans during the course of radiation treatment, to direct radiation to the actual imaging coordinates that were developed during the treatment planning phase of radiation therapy.
  • RMM refers to respiratory motion management systems in radiotherapies that account for the movement of the chest wall, diaphragm muscle, and other structures that move during breathing, so that the radiation still gets to the right spot even though the target area is moving. 
  • 4D CT simulation makes use of the same principle as in RMM in that the scan is acquired while the patient breathes, and the targeted volume takes into account all positions of the tumor during the imaging study, over time.

What Is Proton Beam Therapy (PBT)?

Some cancer centers are beginning to use radiation machines that deliver proton beams instead of photons, or x-rays.

Proton beams are a stream of positively charged particles that deliver energy within a short distance. In theory, protons may reach tumors deep within the body with less harm to nearby tissues.

Organizations such as the National Comprehensive Cancer Network, or NCCN, are beginning to incorporate proton beam therapy, or PBT, in guidelines and recommendations. For instance, in regard to certain cases of peripheral T-cell lymphomas, the NCCN radiotherapy compendium notes include a reference to protons and other newer techniques to "achieve highly conformal dose distribution important for curative patients with long life expectancies;" that is, get the radiation to the right places and spare the surrounding tissue.

The Need for Precision

So far, PBT is not routinely recommended in the treatment of lymphoma. For patients with lymphoma, however, a technique such as proton therapy might some day be preferred to photons in certain cases and for a variety of reasons. Although effective, chemotherapy used to treat lymphomas can have some toxicity to both heart and lungs, which are sensitive to both the effects of chemotherapy and radiation.

Chemotherapy and radiation are often planned together, but they are administered separately, and often, one will follow the other in the treatment of lymphoma.

Proton therapy is designed to reduce the exposure to healthy tissues, which may reduce subsequent side effects. Many patients with lymphoma are younger when diagnosed and live long lives after treatment, so they are at risk for late emerging, long-term side effects associated with standard therapies.

Based on what is known about proton therapy, many believe side effects will be reduced compared to conventional therapy. Doctors and researchers are also working on the chemotherapy side of the equation, exploring the use of newer agents with fewer side effects, looking to any impact on long-term outcomes and late side effects.

Patients with Hodgkin lymphoma in particular, have high cure rates, but they also tend to develop treatment side effects from the chemotherapy and radiation. In fact, childhood HL survivors are one of the groups at most risk for severe or life-threatening chronic health conditions, such as a second cancer or heart disease.

These increased risks are believed due at least in part to the late effects from chemotherapy and from radiotherapy.  

Because proton therapy is designed to be more precise in delivering radiation, the hope is that less heart disease and fewer second cancers will develop. So far, in one study, the incidence of second cancers among those treated with proton versus photon radiation appeared to be similar, but data are limited and more research is needed.

Oncologists Cite Balancing Act

Oncologists who support the use of proton therapy for HL have pointed to the “balancing act” between relapse due to inadequate therapy and severe late toxicities from overly aggressive treatment. Some say that if you increased the chemotherapy to offset for not having radiation therapy, you would likely not make any gains in terms of long-term toxicities; they also highlight the importance of ‘freedom from a second relapse’ as an outcome measure.

According to Hoppe and colleagues, proton therapy provides lower overall radiation doses to the heart, lungs, breasts, esophagus, and other structures for the vast majority of HL patients. Only time will tell if proton therapy will become increasingly routine.

Sources:

Chung CS, Yock TI, Nelson K, Xu Y, Keating NL, Tarbell NJ. Incidence of second malignancies among patients treated with proton versus photon radiation. Int J Radiat Oncol Biol Phys. 2013;87(1):46-52.

Hoppe BS, Flampouri S, Su Z, et al. Effective dose reduction to cardiac structures using protons compared with 3DCRT and IMRT in mediastinal Hodgkin lymphoma. Int J Radiat Oncol Biol Phys 2012;84:449-455. 

NCCN Radiation Therapy Compendium.

Continue Reading