The Cobalt "Bomb": The Beam Source That Replaced Radium and the Noise in Its Name (1951-1954)

The Cobalt "Bomb": The Beam Source That Replaced Radium and the Noise in Its Name (1951-1954)

A physicist, a machine shop

Harold Johns took up his post at the University of Saskatchewan in 1945 as Canada's first full-time cancer physicist (according to the Encyclopedia of Saskatchewan). The university had treated its first patient with the betatron in 1949 (29 March 1949); the cobalt idea was added alongside it in those years. It is said that Johns learned of the cobalt-60 source at Chalk River Laboratory in 1946; another source records that in July 1949 he requested about 1,000 curies of cobalt-60.

Cobalt-60 was obtained by irradiating natural cobalt-59 with neutrons in the NRX reactor at Chalk River. The body of the machine was built by John MacKay of the Acme Machine and Electric company in Saskatoon. Sylvia Fedoruk carried out the calibration that made the machine's dose calculable before any patient was irradiated.

The same autumn, two cities

The same autumn another machine was being readied in Ontario. According to the Western News article, the cobalt-60 source was installed at Victoria Hospital on 16 October 1951; staff of the National Research Council had calibrated the source in advance. The first cancer treatment took place on 27 October 1951 under the clinical direction of Ivan Smith. This machine was the work of Atomic Energy of Canada Ltd. and the Eldorado Mining Company, and according to the same article it was called the "Eldorado Cobalt Bomb".

From here comes the first question of "first": the first treatment with cobalt-60 took place in London on 27 October and in Saskatoon on 8 November. The University of Saskatchewan, for its part, presents its machine as the "world's first calibrated cobalt-60 unit". Western News calls Johns the "inventor" of cobalt machines while also noting that Saskatoon's first treatment came after London's. So I limit the "first" claims: the first recorded treatment is in London, the claim of the first unit calibrated over eleven weeks is in Saskatoon. How the two groups were related is also told differently in the sources; the detail is in the fact-check box.

The rivalry in the press is on record too. The Saskatoon Star-Phoenix answered the London Free Press's claim of "the world's first cobalt bomb" with an editorial titled "The Cobalt 'Bomb'". The date of the editorial conflicts within the source (7 March and 7 November 1951); since the machines were installed between August and October 1951, I think it cannot have been March and that it was November.

The tumor instead of the skin

The problem of radium units is summarized in the 1951 Nature paper by Johns and his team: small radium sources give little radiation; to obtain an adequate dose rate the source has to be brought within a few centimeters of the tumor, and then the skin receives more dose than the tumor, and the dose falls steeply with depth. The same paper carries the title "1,000-curie cobalt-60 units". A strong, high-energy source can be placed far from the patient; the dose reaches deep while the skin is relatively spared. I take this detail about sparing from a photo caption in the University of Toronto magazine and from general radiation physics; I did not read the body of the original paper.

Cobalt-60 emits two gamma rays (1.17 and 1.33 MeV; about 1.25 MeV on average). The earlier X-ray tubes were in the 50-150 keV range and could treat only superficial tumors. Radium was strong but scarce: according to a secondary source, in 1937 a gram cost 25,000 dollars and there were about 50 grams in the world for teletherapy. Cobalt made the dose rate and depth reaching the tumor no longer dependent on the scarcity of radium.

The third story: Grimmett

A third story, independent of Ontario and Saskatoon, is in Houston. The British medical physicist Leonard Grimmett had come to M.D. Anderson. According to a summary of Peter Almond's biography of Grimmett, Grimmett may have been the first person to publish, in 1950, the design of a cobalt-60 unit; Almond also argues that J. S. Mitchell's 1946 paper started the cobalt era. Grimmett lost his life to a heart attack at the age of 49 on 27 May 1951, before the machine was finished. The unit was moved from Tennessee to Houston under police escort in September 1953; the first patients were treated on 22 February 1954 (M.D. Anderson's own history page). The cobalt had been irradiated to 800 curies in Canada.

R. Lee Clark's view was that the original idea and design belonged to Grimmett and Gilbert Fletcher; Canada, for its part, later claimed to be "first". I do not resolve this conflict: who first published the design, who treated the first patient, and who installed the first calibrated unit are three separate questions, and each answer points to a different place.

Cobalt at Çapa

I could not find a verified source on when the first cobalt teletherapy machine came to Türkiye. Two texts on the history of radiotherapy published in the Turkish Journal of Oncology mention a cobalt-60 afterloading device: one says it was installed at Çapa in 1964, "third in the world"; the other writes that it entered service at the end of the 1960s. The two do not agree, and both are brachytherapy devices, not teletherapy "bombs". I could not reach the titles and authors of the texts because access to the site is restricted. A general inference (not from a source): cobalt-60 devices are still used in many countries today; for the patient what matters is less the name of the machine than the oversight of planning and calibration.

This article is Day 128 of the "365 Days of Cancer History" series and tells the emergence of cobalt-60 teletherapy machines around 1951 as a historical event. It is historical-popular content; it is not a diagnosis or treatment recommendation. Consult your physician for decisions about your health. Sources have been verified; details that rest only on a secondary source are noted in the fact-check notes.