Review Outlines Recent Advances in Radiotherapy for Cancer

A new review article published in the New England Journal of Medicine (NEJM) explores recent developments in the field of radiotherapy that have improved survival and quality of life for patients with cancer.

The review, written by Deborah E. Citrin, MD, of the National Cancer Institute, explains that radiotherapy is administered to 470,000 patients in the United States annually, including up to half of all patients with cancer who are treated with radiation to not only eliminate tumors but also alleviate side effects like pain. The last review of radiation oncology in NEJM was published in 1995, but considering the numerous technological and clinical discoveries since then, the topic is due for a revisit.

First, Citrin describes how new imaging techniques have made it easier for radiation oncologists to discern the borders of a tumor, which then allows them to deliver highly targeted doses of radiation. Technologies that modulate the intensity and area of the radiation as it is delivered have enabled clinicians to administer a dose that conforms to the targeted tumor while sparing the surrounding healthy tissues.

The ability to precisely conform doses to the tumor has lessened the need for fractionated treatments, which are split into several doses to allow the healthy tissue time to recover between treatments. The newer techniques, known as stereotactic body radiation therapy, can be delivered at high doses over just 1 to 2 weeks. Clinical trial results are promising; one study found that hypofractionated radiotherapy was as effective in treating prostate cancer compared with traditional therapy, and also more convenient for patients.

Proton and heavy ion therapy have gained attention as potential breakthroughs in radiotherapy as they may reduce the amount of radiation reaching beyond the target. However, more data are needed to prove their efficacy over traditional photon therapy. The innovation that has enabled the most targeted delivery of radiation is brachytherapy, which involves implanting radioactive sources in a body cavity or tumor. Citrin reports that it is now used as a key therapy option for several cancers.

Advances in reducing the toxicity of systemic therapies like chemotherapy have allowed clinicians to lower the dosage and volume of radiation delivered as part of a combination therapy regimen. The reduced doses of radiotherapy may help prevent long-term toxicity and lower the risk of second cancers, although it will take many more years’ worth of data to draw conclusions.

Researchers have also made great strides in enhancing the body’s response to radiotherapy, Citrin writes, highlighting the ways in which immunotherapy and radiotherapy could be used in combination. Ongoing studies are attempting to find the optimal doses and types of each to balance the immunogenic and immunosuppressive effects of radiation.

Finally, advances in imaging and treatment delivery have already helped decrease the toxicity experienced by patients receiving radiation, and researchers continue to develop a better understanding of the drivers of toxicity. Potential pathways that may be targeted for reducing toxicity include the cellular senescence process and the TGF-β cytokine pathway.

“A rapid evolution of technology has progressively increased the safely deliverable radiation dose, minimized exposure of uninvolved normal tissue, increased the accuracy of tumor delineation, and substantially reduced the expected toxicity of treatment,” Citrin concludes. “As a consequence, the toxicity of radiotherapy has consistently decreased, and escalated radiation doses have, in many cases, led to improvements in disease control.”