Particle Therapy
Eric Ford in Primer on Radiation Oncology Physics, 2020
The cyclotron, the older of the two, uses a high-frequency oscillator and a magnetic field to accelerate charged particles (Figure 24.1.13). The cyclotron has two half circles to which an electric field is applied. The particle, a proton say, moves due to the force of this field. The magnetic field is oriented perpendicular to the path of the proton. Therefore, as the proton moves it experiences a force and is bent to travel in a circle (recall from Chapter 1 that magnetic fields exert forces on charged particles). As the proton travels through the system its energy increases due to the applied electric field. Therefore, it travels in a spiral with increasing radii. Recall that particles with higher energy travel in circles with larger radii. By picking off the proton at a specific radius, the energy can be selected. Modern cyclotron design employs superconducting magnets with magnetic fields of 5–10 T, making them very compact.
Activation Techniques
Frank Helus, Lelio G. Colombetti in Radionuclides Production, 2019
Most of the manmade radionuclides created by charged particles are produced by a cyclotron or other type of accelerator.16 The cyclotron is essentially a high-voltage ion accelerator in which the ions are constrained to follow a spiral pathway by the presence of a magnetic field applied perpendicularly to the plane of ion motion (the principal of operation of the cyclotron and related accelerators are described later on). In general the radionuclides generated by charged particle bombardment are neutron defficient isotopes, and so tend to be those radionuclides which decay by β+ emission-positron emitters; or decay by electron capture, or both. The nuclear reactions which occur on the cyclotron are varied and each nuclear reaction induced by charged particles has an optimum energy range for the bombarding particle, that produce the best results in terms of the yields or purity of desired product and minimum of co-produced contaminants. For some elements there is practically no reactor-produced radionuclide with properties suitable to make it of value as a tracer for biological studies. Some examples of radionuclides commonly produced at cyclotron installations are given in Table 3.
Accelerators for Protons and Other Heavy Charged Particles
W. P. M. Mayles, A. E. Nahum, J.-C. Rosenwald in Handbook of Radiotherapy Physics, 2021
Figure 15.1 presents a schematic diagram of a cyclotron, conceived and patented by E.O. Lawrence in 1932 (Lawrence and Livingston 1932). The ion source (e.g. a plasma produced by an electric arc from a tungsten filament in hydrogen gas) injects the protons into the centre of the machine. A high-frequency alternating high voltage is applied to two hollow semi-circular electrodes (called dees because of their shape). When a proton is in the electric field between the two electrodes, the sector of negative polarity exerts a force of attraction and therefore, produces acceleration. A magnetic circuit and a set of coils are used to create a strong magnetic field perpendicular to the trajectory of the particle. When the proton re-enters the cavity of the electrodes, no electric force acts on it. The magnetic field B bends the particle of charge q moving with a velocity v into a circle of radius r. It emerges again into the space between the dees exactly when the electric field has changed its direction, being accelerated again and going on a circular trajectory with a larger radius, and so on.
Cohort profile – MSK radiation workers: a feasibility study to establish a deceased worker sub-cohort as part of a multicenter medical radiation worker component in the million person study of low-dose radiation health effects
Published in International Journal of Radiation Biology, 2022
Lawrence T. Dauer, Meghan Woods, Daniel Miodownik, Brian Serencsits, Brian Quinn, Michael Bellamy, Craig Yoder, Xiaolin Liang, John D. Boice, Jonine Bernstein
Later, with collaboration of the US Department of Energy and National Laboratories, a cyclotron (affectionately known as ‘Betsy’), one of the earliest hospital-based cyclotrons in the world and the first in the country, was installed in the SKI laboratory building in order to enable safe research and development and production of other radionuclides for imaging and therapy. Subsequent cyclotrons were installed, including a dual-beam instrument enabling both liquid and solid targets, as well as the most recent Radiochemistry and Cyclotron Facility which routinely produces positron-emitting radionuclides and develops and performs organic synthesis of both single-photon-emitting as well as positron-emitting radiotracers. These facilities were heavily supported by medical health physics engineering, design, and operational assistance to incorporate safety features while facilitating radionuclide production, research, and patient care.
Dr Tikvah Alper: a short history of her scientific career
Published in International Journal of Radiation Biology, 2022
Peter G. Coultas, John W. Hopewell
A National Physics Laboratory had been established in South Africa (circa 1947) and Tikvah returned briefly as Head of Biophysics. Luckily, for the many of us who later benefited from exposure to Tikky, she very clearly let her views be known in a petition against the government erosion of colored Voter’s rights, the start of apartheid in South Africa. The response that this produced meant that she and the family came to settle in England where she again started work as an unpaid fellow at the MRC Experimental Radiopathology Unit (ERU) at Hammersmith Hospital, London. On this occasion, she was given a small MRC grant to continue studies on the irradiation of bacteriophage. At this time (Alper 1952), the Unit had a functioning Van de Graaff generator that could accelerate positive ions as well as well as electrons. It was this machine that enabled the earliest experiments into oxygen effects for damage from fast neutrons (Alper and Howard-Flanders 1956). Over the next few years the facilities in the Unit were further developed with the installation of an 8 MeV Linear Accelerator and, in the MRC Cyclotron Unit, a Cyclotron. The close collaboration between the MRC Units meant that although the cyclotron was used for radiotherapy during the day, it was also made available for experimental studies during the evenings. It was in this environment that Dr Alper’s scientific career finally took off, despite now being well into her thirties and lacking a Ph.D., something that she often used to joke about in later life.
Liquid chromatography coupled to mass spectrometry for metabolite profiling in the field of drug discovery
Published in Expert Opinion on Drug Discovery, 2019
Javier Saurina, Sonia Sentellas
To finish this section, it is worth to mention ion cyclotron resonance analyzers, where ions move in circular orbits in a magnetic field. As in orbitrap systems, each m/z value generates its own characteristic frequency [86]. In spite of the fact that a very high resolving power can be reached with this type of mass spectrometers, the price, complexity and unfriendly character requiring expertise personnel have prevented a more extensive and routine use for drug metabolism profiling. Some recent applications of cyclotron technology addressed the study of metabolites of erysolin (anti-tumor and anti-nerve compound from Brassicaceae) in rat plasma, bile, urine and feces [87], pimavanserin (drug candidate for Parkinson treatment) [88], and a traditional Chinese medicine preparation from Ixeris sonchifolia in the same biological matrices [89].
Related Knowledge Centers
- Particle Accelerator
- Radionuclide
- Synchrotron
- Cockcroft–Walton Generator
- Nuclear Medicine
- Particle Therapy
- Linear Particle Accelerator
- Synchrocyclotron
- Ion Source
- Medical Imaging