Harold E. Johns

Harold Elford Johns (4 July 1915 – 23 August 1998) was a Canadian medical physicist, noted for his extensive contributions to the use of ionizing radiation to treat cancer.

Early life and education
Johns was born to missionary parents in Szechuan, China. He lived in China until 1926, when political unrest prompted his parents to return to North America. After spending time in Tacoma, Washington and Brandon, Manitoba, his family settled in Hamilton, Ontario.

In Hamilton, Johns pursued a degree in mathematics in physics at McMaster University and completed his B.Sc. in 1936. He then moved to the University of Toronto, where he earned an M.A. and Ph.D. in physics in 1939.

Early career
Johns' graduation coincided with the start of World War II. For the duration of the war, he taught physics, mathematics, radar, and radio navigation to newly recruited pilots as part of the British Commonwealth Air Training Plan. Based on his radiography and physics experience, Johns was also involved in noninvasive x-ray testing of metal aircraft castings.

He married his wife, Sybil Hawkins, in 1940. Their marriage lasted until Johns' death fifty-eight years later.

Cobalt bomb
After the close of the war, Johns was invited to work with Ertle Harrington at the University of Saskatchewan. It was there in Saskatoon that he conducted his pioneering research in the use of cobalt-60 as a gamma ray source for the radiation treatment of cancer.

Interest in nuclear technology exploded in postwar Canada. Nuclear research facilities constructed at Chalk River, Ontario near the end of the war were expanded and opened to civilian research projects. The first operational nuclear reactor outside the United States–NRX–was located at Chalk River, and it provided a source of activated cobalt-60 for Johns' experiments.

Two groups–Johns' at the University of Saskatchewan, and another in London, Ontario–designed and constructed external beam radiotherapy instruments using cobalt sources. Ultimately, the first treatment was delivered in London, on 27 October 1951.

In early 1952, Maclean's magazine had dubbed the cobalt-source radiotherapy machine the cobalt bomb&mdash;a tongue-in-cheek tribute to this peaceful use of nuclear technology.

Johns' original device was used in Saskatchewan until 1972.

Ontario Cancer Institute
In 1956, Johns assumed the headship of the physics division of the Ontario Cancer Institute at Princess Margaret Hospital in Toronto.

To further scientific and medical collaborations between radiologists, radiotherapists, physicians, and physicists, Johns guided the creation of the Graduate Department in Medical Biophysics at the University of Toronto in 1958. Johns served as the second Chair of the Department, succeeding Arthur Ham in 1960.

Over the course of his career, Johns supervised sixty-eight graduate students and published more than two hundred peer-reviewed papers.

Awards

 * Officer of the Order of Canada (1978)
 * Emeritus University Professor of the University of Toronto
 * Canadian Medical Hall of Fame inductee (1998)