11 Application of Accelerators and Storage Rings
717
11.3.2 Accelerators and Cancer Therapy
11.3.2.1 History
Conventional Therapy
The roots of brachytherapy (discussed in section 11.3.1.3) and teletherapy date
back to the discoveries of X-rays and radium made by Roengten and the Curies
in the years 1895–1897. X-ray tubes and gamma-ray sources were soon employed
in medical or technological uses. Teletherapy with X-ray photons was performed to
cure superficial tumours few years after the discovery.
The first electron linac was built in 1947 at Stanford by Bill Hansen and his group
for research purposes [65] and was powered by a klystron produced by Varian. Soon
after, this new tool superseded all other electron/photon sources. Also in 1947, in
England, Fry and collaborators build a 40-cm linac that accelerated electrons from
45 to 538 keV [66].
In the years that followed, those two groups and others, in particular the group
of John Slater at MIT, studied the parameters of the irises to improve the power
efficiency of the structure and to adapt the traveling wave parameters of wavelength
and phase velocity. Around 1950 megavoltage’ tubes were built and, complementing
the ‘cobalt bombs’ entered clinical practice. The positive surprise was that, due
to the longer ranges of the electrons—put in motion by the gammas of the beam
mainly through the Compton effect—these ‘high-energy’ radiations had a much
better sparing of the skin.
In those years a process was initiated to adapt the complex machines developed
for research purposes to the clinical environment and to the treatment needs. After
a short season in which the X rays of energy larger than 5 MeV were produced
with medical ‘betatrons’, electron linacs, running at the by-now standard 3 GHz
frequency, became the instrument of choice. Varian in 1960 produced for the first
time a linac that, mounted on a gantry, rotated around the patient and in 1968 the
first medical machine based on standing-wave acceleration.
From the side of the traveling-wave accelerators, further studies have improved
the efficiency and the start up time of the radiation so that today both designs are
still used in medical linac: the two major manufacturers, Varian and Elekta (see
Table 11.5) produce accelerators the first based on standing-wave and the second on
travelling-wave. The average accelerating fields are in the range 10–15 MV/m.
In 2017 about 12,000 [67] linacs are installed in hospitals all over the world and
in the developed countries there is one linac every 200,000–250,000 inhabitants. It
is interesting to remark that all the electron linacs used to treat patients are close, as
far as the overall length is concerned, to the 27 km circumference of LHC.
About 50% of all tumour patients are irradiated as exclusive treatment or
combined with other modalities so that radiotherapy is used every year to treat about
20,000 patients on a Western population of 10 million inhabitants. On average, 40%
of the patients who survive 5 years without symptoms have been irradiated.
717
11.3.2 Accelerators and Cancer Therapy
11.3.2.1 History
Conventional Therapy
The roots of brachytherapy (discussed in section 11.3.1.3) and teletherapy date
back to the discoveries of X-rays and radium made by Roengten and the Curies
in the years 1895–1897. X-ray tubes and gamma-ray sources were soon employed
in medical or technological uses. Teletherapy with X-ray photons was performed to
cure superficial tumours few years after the discovery.
The first electron linac was built in 1947 at Stanford by Bill Hansen and his group
for research purposes [65] and was powered by a klystron produced by Varian. Soon
after, this new tool superseded all other electron/photon sources. Also in 1947, in
England, Fry and collaborators build a 40-cm linac that accelerated electrons from
45 to 538 keV [66].
In the years that followed, those two groups and others, in particular the group
of John Slater at MIT, studied the parameters of the irises to improve the power
efficiency of the structure and to adapt the traveling wave parameters of wavelength
and phase velocity. Around 1950 megavoltage’ tubes were built and, complementing
the ‘cobalt bombs’ entered clinical practice. The positive surprise was that, due
to the longer ranges of the electrons—put in motion by the gammas of the beam
mainly through the Compton effect—these ‘high-energy’ radiations had a much
better sparing of the skin.
In those years a process was initiated to adapt the complex machines developed
for research purposes to the clinical environment and to the treatment needs. After
a short season in which the X rays of energy larger than 5 MeV were produced
with medical ‘betatrons’, electron linacs, running at the by-now standard 3 GHz
frequency, became the instrument of choice. Varian in 1960 produced for the first
time a linac that, mounted on a gantry, rotated around the patient and in 1968 the
first medical machine based on standing-wave acceleration.
From the side of the traveling-wave accelerators, further studies have improved
the efficiency and the start up time of the radiation so that today both designs are
still used in medical linac: the two major manufacturers, Varian and Elekta (see
Table 11.5) produce accelerators the first based on standing-wave and the second on
travelling-wave. The average accelerating fields are in the range 10–15 MV/m.
In 2017 about 12,000 [67] linacs are installed in hospitals all over the world and
in the developed countries there is one linac every 200,000–250,000 inhabitants. It
is interesting to remark that all the electron linacs used to treat patients are close, as
far as the overall length is concerned, to the 27 km circumference of LHC.
About 50% of all tumour patients are irradiated as exclusive treatment or
combined with other modalities so that radiotherapy is used every year to treat about
20,000 patients on a Western population of 10 million inhabitants. On average, 40%
of the patients who survive 5 years without symptoms have been irradiated.