WE-G-105-01: History Symposium: Early Developments in Teletherapy Machines

From Radium Teletherapy to Cobalt‐60 Teletherapy ‐ Peter R. Almond The history of radioisotope teletherapy machines will be traced from the beginning of the twentieth century, when radium was used, to the widespread use of cobalt‐60 machines in the 1970s and 1980s. Some early radium teletherapy machines will be discussed showing their development up to around 1940. By then their limitations were well understood and as early as 1937 a suggestion was made that an artificial radioisotope might be found to replace the radium. Although cobalt‐60 was recognized fairly early as a possible candidate, it was not until World War II and the introduction of the nuclear reactor that a suitable source of cobalt‐60 was identified. Following the war cobalt machines were developed in Canada and the United States resulting in commercial units being available primarily from Atomic Energy of Canada Limited and in the U.S. the Picker X‐ray Company. However cobalt‐60 machines were not the first artificial radioactive teletherapy treatment units. The first to treat a patient was a radioactive iridium machine built in the United Kingdom. Because radioactive cesium‐137 was readily available it was also used in treatment machines. Both the iridium and the cesium units were short SSD machines with various problems associated with such machines. They could be considered the logical development of the radium units, with the radium being replaced with the radioactive isotope. The cobalt units were a complete departure from the radium machines. The source size and the activity available allowed the cobalt units to be developed as a replacement for orthovoltage X‐ray units. The clinical implications of this will be presented. Cobalt‐60 units reached their peak use around 1980, but there were inherent problems with them and they have now been mainly replaced with linear accelerators. Early X‐Ray Therapy Machines ‐ Colin G. Orton In January, 1896, just months after Roentgen discovered X rays, the 1st cancer patient treatments began. Unfortunately, the majority of radiation treatments were not for cancer but for many other purposes, such as removal of hair and the treatment of acne, eczema, migraines, etc., many with dire consequences. Even when used to treat cancer, there were often tragic effects due to the use of very crude equipment during the 1st 20 years of X‐ray therapy. The machines were often unshielded, with several patients and staff in the room being exposed to scattered radiation. Hundreds of the early pioneers (the “Martyrs of Radiology”) died of radiation‐induced cancers. Also, since X‐ray energies were relatively low (80–120 kVp) and outputs extremely low and highly unreliable, most treatment schedules lasted months and had to be individualized based on skin reactions. Untoward reactions were commonplace. It was not until the advent of the Coolidge hot‐cathode X‐ray tube in 1913 that higher outputs could be achieved and controlled, and energies could be increased such that standardized schedules could be prescribed and deeper cancers treated. Prior to this, the low‐energy machines (later called “superficial X‐ray units”) were really only suitable for the treatment of skin lesions. It was not until the 1920s that “deep” therapy machines of energies 120 – 300 kVp (initially often referred to as “cannons” but later to be called “orthovoltage X‐ray units”) began to be developed for the treatment of deeper lesions. These usually used bearings and cranks to adjust tube position and angulation so that patients could be treated from different directions. By 1930 the quest for higher‐and‐higher energy machines began. The 1 st of these were “supervoltage” X‐ray machines built for radiotherapy between 1930 and 1934. These included machines of 500 kVp installed at Harper Hospital, Detroit, 600 kVp at Caltech, 750 kVp at Memorial Hospital, New York, 800 kVp at Mercy Hospital, Chicago, and 1,000 kVp at Swedish Hospital, Seattle and Caltech. These were enormous machines. The 1,000 kVp unit at Caltech, for example, occupied a vault 42 m long, by 20 m wide, by 15 m high, with the treatment room, where up to four patients could be treated simultaneously, situated above the ceiling. In the pursuit of more compact machines with even higher energies, John Trump and colleagues in Boston developed the 1st Van de Graaff machines for therapy. A 1 MeV unit was installed at Huntington Hospital in 1937 and soon ceiling‐mounted machines of energies up to 2 MeV were developed. These could be rotated about a horizontal axis aimed at a patient sitting in a chair that could be rotated about a vertical axis. Multidirectional, and even rotational, megavoltage X‐ray therapy was born. By 1965, about 40 Van de Graaff radiotherapy machines were in use worldwide, but their energies were restricted to just a few MeV. The betatron, on the other hand, was capable of much higher energies. The 1st betatron used for radiotherapy was a 6 MeV machine built by Konrad Gund at Siemens, Erlangen, Germany and reportedly used to treat a patient in 1942, but there is little documentation of this. Elsewhere, the 1st well‐documented treatments were with the 24 MeV betatron built by Donald Kerst at the University of Chicago and developed for therapy in 1948 by Lester Skaggs, John Laughlin, Gail Adams, Larry Lanzl, and colleagues. Although over 100 betatrons were being used for radiotherapy up until about 1970, because they were bulky machines, not amenable for isocentric mounting, and with a low X‐ray output, they were soon replaced by linear accelerators for high energy X‐ray therapy. Linacs grew out of the development of klystrons in the USA and magnetrons in the UK in the 1930s, but much of this development was kept secret during the 2nd World War due to their use in radar. It was not until late 1946 that the 1st linac (0.5 MeV) was developed by Fry and colleagues at the Atomic Energy Research Establishment in Harwell, UK, and in early 1947 by Bill Hanson, Stanford University, California and Varian Associates (1.7 MeV), which was soon increased to 4 MeV by late 1947. The 1st therapy linac was an 8 MeV stationary machine built by Metropolitan Vickers and installed at Hammersmith Hospital, London, with the 1st patient treated on 19 August, 1953. Later that year, a 4 MeV isocentric machine was installed by Mullard Research Laboratories at the Newcastle General Hospital. The 1st linac for radiotherapy in the USA was a 6 MeV machine built by Varian, which began patient treatments at Stanford in 1956. This was the predecessor of the Clinac 6, a fully rotational linac, introduced by Varian in 1960, and later the Clinac 4, which used standing‐wave technology to reduce size, complexity and cost, which became the workhorse of radiotherapy in the USA in the 1970s. Modern, linear‐accelerator based high‐energy X‐ray therapy had been born. Learning Objectives: 1. Understand the early development of teletherapy treatment machines 2. Understand the benefits of the evolution from radium to cobalt sources for teletherapy 3. Understand the advantages and disadvantages of early x‐ray treatment machines