The role of radiation therapy in the treatment of metastatic cancer.

Radiation therapy continues to play an important role in the management of cancer. In this review, we discuss the use of radiation therapy to target and control micrometastatic disease (adjuvant use of radiation), or using stereotactic radiation therapy to address small volumes of gross disease, such as oligometastases, and finally the use of radiation therapy in the era of immunotherapy. Radiation therapy is commonly used to treat nodal basins suspected of harboring microscopic disease. More recently, computer and technical innovations have allowed radiation oncologists to treat small volumes of gross disease within the brain and also in the body with great success, adding to the cancer armamentarium. This modality of cancer treatment that began shortly after the discovery of X-rays by William Roentgen continues to evolve and finds new clinical applications which minimize toxicity while increasing effectiveness. The newly discovered interactions of high dose/fraction radiation (stereotactic radiosurgery) with immune check point inhibitors in melanoma is the latest example of how synergism can be achieved between two different modalities thus increasing the therapeutic ratio to control metastatic cancer.