del Regato, Juan A. (01 March 1909–12 June 1999), oncologist, was born Juan Angel del Regato in Camagüey, Cuba, the son of Juan del Regato, an electrical engineer, and Damiana Manzano del Regato. After attending both public and private schools in his native city as well as in Nuevitas and Santa Clara, Cuba, and Mérida, Mexico, he entered the University of Havana in 1926 as a premedical student. In Havana del Regato supported himself by working as an extern, a medical photographer, and later as an X-ray technician, and when the university was forced to close in 1930 because of political unrest, he continued his education at the University of Paris with the financial support of the Cuban League of Cancer.

Del Regato's years in Paris were both busy and fulfilling. In addition to his work at the University—where he focused on oncology—he also studied at the Radium Institute, where he was influenced by Antoine Lacassagne, Claudius Regaud, and, particularly, Henri Coutard. After interning at the institute in 1934–1935, he spent the following year as a research fellow at the Curie Foundation and also assisted Coutard in a series of lectures given in the Soviet Union. He returned to the Radium Institute as Coutard's assistant in 1937, the same year in which he graduated from the University with a doctor of medicine degree and a diploma of radiophysiology and radiotherapy. His thesis, concerning radiotherapy for inoperable maxillary sinus cancer, represented the first report on nonsurgical treatment of the disease, and del Regato also contributed to medical technology with his development of the Regato Localizer, a lighting device designed to facilitate X-ray directional guidance during radiation therapy. Although unpatented by del Regato—who actually donated the rights to his device to several radiotherapy machine manufacturers—the device was later adopted for use in both cobalt 60 radiotherapy machines and linear accelerators.

In 1938 del Regato came to the United States and served as Coutard's assistant at the Chicago Tumor Institute before relocating later in the year to Washington, D.C., where he worked with Edwin A. Merritt at the Warwick Cancer Clinic and developed a set of specula and adapters that enabled the development of a highly effective X-ray treatment of uterine cancer. (On 1 May 1939 he married Inez Gertrude Johnson; the couple eventually had three children.) In 1941—the year in which he became a naturalized citizen—del Regato moved to the National Cancer Institute at the U.S. Marine Hospital in Baltimore, Maryland, where he served for two years as a research fellow and radiotherapist. In 1943 he relocated yet again, this time to Columbia, Missouri, where he served as chief radiotherapist at the Ellis Fischel Cancer Hospital. In January 1949 he became the first medical director of the newly established Penrose Cancer Hospital in Colorado Springs, Colorado. Established by philanthropist Julie V. L. Penrose in conjunction with the Sisters of Charity as a memorial to her husband, Spencer Penrose, the institution soon became a world-class facility under del Regato's leadership. In 1949 he established an annual seminar that featured fifteen cancer case studies under discussion by a panel of experts with the additional input of previously-submitted diagnostic opinions by a worldwide network of experts. In 1950 he began one of the first training programs for radiotherapists in the United States. During the first twenty years of its existence, Penrose produced twice as many radiotherapists as any other institution, and the program was soon emulated throughout the United States.

It was in the treatment of prostate cancer, however, that del Regato made his greatest impact. At the time he began working in the area in 1958, 95 percent of the diagnosed cases were inoperable, and radiation was considered an ineffective form of treatment. By careful observation, del Regato noticed that this type of cancer was not resistant to radiation treatment; rather, being slow-growing by nature, it was merely slow to respond to treatment. By 1966, the Committee for Radiation Therapy Studies had approved a protocol for treatment using del Regato's methods, and in the following year the National Cancer Institute sponsored an extensive study at forty-two medical institutions. All in all, over 300 cases received treatment, and, with results verified over a period of years, del Regato was able to present his findings at the International Congress of Urology in July 1973.

Having served as professor of clinical radiology at the University of Colorado Medical School since 1950, del Regato took a similar position at the University of South Florida in Tampa, where he remained until his retirement in 1983. The author of numerous professional articles, he also authored Cancer: Diagnosis, Treatment, and Prognosis (1947, with Lauren V. Ackerman), which went into several editions and became a standard text in the field (later titled Ackerman and del Regato's Cancer: Diagnosis, Treatment, and Prognosis). A member and a correspondent of numerous professional associations, he was a founder and later president (1974–1975) of what is now the American Society for Therapeutic Radiologists and Oncologists, and also served as president of the Inter-American College of Radiology (1967–1971), the American Radium Society (1968–1969), and the International Club of Radiotherapists (1963–1965). Del Regato was the recipient of a host of awards for his work, including the Gold Medal of the American College of Radiology (1968), the Janeway Gold Medal from the American Radium Society (1973), and the Bruninghaus Prize from the French Academy of Medicine in 1979. During his long career del Regato also served as a consultant for a variety of institutions, including the Veterans Administration, the Vincent T. Lombardi Cancer Research Center at Georgetown University, and Denver's Milheim Foundation. After spending his final years in a Tampa retirement home, he died in Traverse City, Michigan, while visiting one of his daughters.

In a lifetime devoted to fighting cancer, Juan del Regato made or contributed to significant advances in diagnosis, treatment, and technical equipment. His leadership at Penrose Cancer Hospital resulted in perhaps his most valuable legacy: the many radiotherapists for whom his program at Penrose provided the template for training others.