By Dr. Dennis Mah
Patients battling cancer are living longer than ever before.
In 2018, there were 15.5 million cancer survivors in the U.S. An amazing accomplishment and testament to medical innovation no doubt, but it has also led to new challenges for oncologists—caring for patients who may experience later-in-life side effects of their cancer treatment.
As the population of cancer survivors grows and continues to age, the occurrence of secondary cancers has risen dramatically —from 9% of all cancer diagnoses in 1975-1979 to 19% in 2005-2009. Moreover, research has found that the risk of developing a secondary tumor or a complication increases as the dose of radiation increases.
Used for decades, conventional radiation, or x-ray therapy, is a common form of cancer treatment for solid tumors because of its effectiveness in controlling the growth of cancer cells. The primary x-ray photons produce secondary electrons that deposit their energy along the entire path of the treatment beam. While effective at eradicating cancer, traditional radiation, in some cases, may result in long-term side effects. Depending on where the patient’s tumor is located, side effects can include heart and lung issues, hypothyroidism, intestinal problems, infertility, cognitive issues, and increased risk of developing other cancers. Fortunately, new tools and approaches have developed in recent years that have permitted delivery of more tailored, precise radiation treatment through improved target definition and delivery.
Amongst these approaches is proton therapy. Conventional radiation treatment uses x-rays while proton therapy uses protons—dense, positively charged atomic particles—to destroy cancer cells. Protons deposit most of their energy at precise depths, ensuring that the peak radiation dose (called the Bragg peak) hits the tumor and stops. By changing the proton energy, the radiation dose can be sculpted to minimize interaction with nearby healthy organs. In contrast, x-rays pass right through the patient’s body, penetrating well beyond tumors and depositing radiation into healthy tissues, increasing chances of developing secondary cancers. A recent paper suggests that protons reduce incidence of secondary cancers compared to x-rays.
For young cancer patients, the benefits of precise radiation cannot be understated. Children are more susceptible to damage caused by radiation than adults because they have a longer life over which to develop secondary malignancies. Research suggests that the risk of developing secondary cancers is correlated to age at the time of treatment. Young girls exposed to radiation have the highest chance of developing breast cancer later in life, whereas there is little or no increase in risk among women ages 40 or older. Proton therapy’s precision means it reduces the risk of secondary radiation-induced cancer and developmental abnormalities. Researchers recently found that proton therapy was effective at reducing tumors and demonstrated minimal toxicity to surrounding organs in treating pediatric patients with high-risk neuroblastoma.
Similarly, proton therapy is an effective treatment option for breast cancer, especially for treatment of cancer to the left breast, because of the tumor’s proximity to the heart. A recent study showed that patients with left-sided breast cancer may be more likely than patients with right-sided breast cancer to develop cardiovascular diseases. This is supported by a recent publication that shows that the risk increases with average radiation dose to the heart. Protons permit a direct treatment of the breast tissue and then stop before they enter the heart or lungs. In contrast, x-rays use a tangential approach that includes a portion of the heart and lungs.
Physicians must establish a long-term relationship with cancer patients to effectively monitor their health and address complications before they escalate. A multidisciplinary approach with long-term follow up may result in better outcomes.
With the continued advancement of medical technology, physicians are tasked with adopting new strategies to mitigate potential long-term consequences and preserve quality of life among patients. As new approaches result in longer lives, side effects that were not previously seen now need to be managed. Sole treatment of current conditions is no longer sufficient. As more research becomes available on the efficacy of innovative treatments like proton therapy, we anticipate further adoption of these technologies.
Dr. Dennis Mah is the physics director at ProCure Proton Therapy Center in Somerset, NJ. He is a former professor at Fox Chase Cancer Center, Columbia University and Albert Einstein College of Medicine. Dennis holds a PhD in medical physics from the University of Toronto and was a clinical fellow at Memorial Sloan Kettering Cancer Center.