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The Positive Power of Protons

Babita Jyoti, M.D.

July 1, 2022

Radiation therapy is a major cancer therapy that can be used alone, with surgery, and/or chemotherapy to cure localized cancers. Proton therapy is one of the most advanced forms of radiation therapy. Ackerman Cancer Center is 1 of only around 30 centers in the United States that uses this specialized form of cancer treatment.

In 1919, while working in Manchester, England, Ernest Rutherford discovered that using alpha particles from a radioactive source to blast the nucleus of certain elements, such as nitrogen gas, led to the disintegration of the nucleus and the emission of ‘fast protons’. Since this discovery over 100 years ago, we have come a long way in the application. We are fortunate to have this specialized form of cancer treatment here in our community at Ackerman Cancer Center. I was fortunate to have had the opportunity to complete my Fellowship training in this advanced modality.

Proton beam therapy is a highly targeted form of radiation therapy that uses protons instead of photons (or x-rays) to target a tumor with precision. A proton beam can deposit the majority of its energy at depth. In treatments using this technology, a proton beam is designed to come to a stop immediately after it deposits the majority of the dose directly at the tumor site. This reduces damage to surrounding tissue and minimizes side effects for patients. This is extremely important when treating tumors close to critical structures such as the brain, eyes, spinal cord, heart, lungs, kidneys, bowel, etc. This enables elimination of the exit dose of radiation, spares critical structures, and decreases total radiation exposure. This overall decrease in radiation dose translates into fewer secondary cancer risks from radiation exposure. An advantage of a decrease in radiation dose to surrounding normal tissue leads to a decrease in the immediate and late effects of treatment. As a result, this causes a more tolerable treatment which in turn helps in completing the course of treatment.

2 Key Benefits of Proton Therapy Include:

  1. Enabling a higher dose of radiation to the tumor/cancer while keeping the dose to adjacent organs constant.
  2. Enabling less toxicity by keeping the dose to adjacent vital organs at its lowest.

Cancers are varied and differ in their biology and behavior. We have studied the behavior of cancer for decades now and understand that some cancers require a higher dose of radiation for eradication whereas some may require lower doses. As we cure more and more cancers and see patients survive longer, we must reduce the side effects of cancer treatments. Proton therapy helps us achieve both of these critical goals of eradicating cancer and improving survivorship. Let me elaborate on this with a few specific examples of some situations where we use proton therapy.

Brain and Spinal Cord Tumors – The brain is a compact structure that controls vital body functions. Precision in treatment is of the essence. The ability to use proton therapy is particularly important when tumors are near the eyes, the base of the skull where we see important cranial nerves traverse, and structures like the brain stem, etc. Not only can we treat malignant tumors of the brain, but also some benign tumors that may not be amenable to surgical removal. This is true not only of tumors that originate in the central nervous system but also of soft tissue sarcomas in close relation to the spinal cord.

Breast Cancer- The treatment of breast cancer is becoming hugely successful due to advanced and sophisticated screening methods like contrast-enhanced mammography and extensive research and collaboration between cancer treatment teams. Radiation is an essential modality in the treatment of breast cancer and is used to target breast tissue in patients who undergo lumpectomies, chest walls in patients treated with mastectomy, and the lymph node regions when at risk. Radiation dose to the lungs can be significantly decreased by using proton therapy. In left-sided breast cancer, protecting the heart is essential. As screening improves and our pick-up of early breast cancer improves, women can live longer. Heart disease is an important cause of morbidity and mortality with age. Studies have shown that exposure to each 1 Gy of radiation increases the risk of coronary artery disease by 7%. Proton therapy offers the promise of negligible doses to the heart making it prudent to use this modality in such cases.

Prostate cancer-  1 in 8 men are diagnosed with prostate cancer in their lifetime. It is the second leading cause of death in men, after lung cancer. Early detection is possible with screening and treatments are extremely effective. This means that we can detect this early and treat it effectively and cause a significant positive impact on the men’s health and cancer burden in the world. Proton therapy is a non-invasive, effective, and valuable treatment as it leads to successful outcomes with vastly lesser side effects both during treatment and in the long run.

Head and Neck Cancer-  Head and neck cancers, although usually curable, usually are at the cost of tremendous adverse effects both from cancer itself and also from treatment. Head and neck cancers are of several different types depending on the site of origin. Generally speaking, radiation is an essential modality of treatment and is sometimes used with concurrent chemotherapy or after extensively debilitating surgery. In these cases, reducing the effects of treatment is critical. A large number of patients may require the placement of a feeding tube during treatment. It has been proven that this can be reduced with the use of proton therapy. There is also evidence that treatment with proton therapy helps improve the tolerability of this intense treatment.

Lung Cancer-  Early lung cancer treatment with radiation alone has been extremely successful, as has treatment of more locally advanced lung cancer with radiation and concurrent chemotherapy. Sparing adjacent normal lung tissue is critical in these patients and is easily achieved with proton therapy. In a patient receiving both chemo and radiation, treatment effects can be severe leading to difficulty in completing the course of treatment. In such cases, proton therapy is extremely beneficial, and we have seen improved tolerability and thus compliance. The spinal cord, esophagus, heart, and in some cases the liver, are other vital organs that can be spared with the use of proton therapy.

Lymphoma – Treatment of lymphoma depends on the specific type and there are far too many kinds of lymphoma. Lymphomas tend to respond extremely well to radiation therapy and thus are used often. As lymphomas are extremely sensitive to radiation, the dose of radiation required is usually much less than with most other cancers. We see many young patients with lymphoma who can be cured with successful multi-modality treatment such as the sequential use of chemotherapy and radiotherapy. It is again important to limit the overall dose of radiation in such patients. Lymphatics can be found almost anywhere in our bodies, and so can lymphoma. Proton beam therapy can thus be used to overcome the proximity to vital organs.

The above are only a few examples of the use of proton therapy. There are several other cancers where protons can offer the promise of a positive outcome such as pancreatic cancer, eye tumors, rectal cancer, liver cancer, gynecological cancer, bladder cancer, soft tissue, and bone sarcomas.

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