Hadron accelerators for radiotherapy

Abstract

Over the last twenty years the treatment of cancer with protons and light nuclei such as carbon ions has moved from being the preserve of research laboratories into widespread clinical use. A number of choices now exist for the creation and delivery of these particles, key amongst these being the adoption of pencil beam scanning using a rotating gantry; attention is now being given to what technologies will enable cheaper and more effective treatment in the future. In this article the physics and engineering used in these hadron therapy facilities is presented, and the research areas likely to lead to substantive improvements. The wider use of superconducting magnets is an emerging trend, whilst further ahead novel high-gradient acceleration techniques may enable much smaller treatment systems. Imaging techniques to improve the accuracy of treatment plans must also be developed hand-in-hand with future sources of particles, a notable example of which is proton computed tomography.

Current and future accelerator technologies for charged particle therapy

“…To cover this canonical 10 to 20 cm depth in water requires proton energies from about 112 to 166 MeV, and 1 Gy of dose in this litre volume requires around 90 billion protons (90 Gp) of 22 pJ average energy, or about 16 nC of charge [37]. Appropriate intensity weighting of the different-energy spots allows a homogenous dose to be obtained within the PTV; this technique is known as Intensity-Modulated Proton Therapy (IMPT).…”

“…Similarly, multiple coulomb scattering (MCS) will spread the protons out transversely, and again an initial incident spot size of a few millimetres is adequate; this translates to an emittance requirement of around 10 mm-mrad. These beam specifications are readily achieved by conventional accelerator technology as will be seen below [40,37,41].…”

The PyZgoubi framework and the simulation of dynamic aperture in fixed-field alternating-gradient accelerators

“…Similar to cyclotrons, FFAGs allow high-intensity beams to be rapidly accelerated. FFAGs may be advantageous in several applications: accelerating unstable particles such as muons, where the FFAG offers both a much smaller acceleration time and a larger beam acceptance than a synchrotron [5,6]; accelerating intense proton beams to c GeV energies for applications such as spallation neutron production or to drive accelerator-driven subcritical reactors, where cyclotron designs have been found to be difficult [7,8]; production of either protons or light ions for hadron therapy, where the high (c kHz) extraction rate may allow better pulse-by-pulse variation of the delivered energy to a patient [9][10][11][12].…”

Medical therapy and imaging fixed-field alternating-gradient accelerator with realistic magnets

“…Supplanting early facilities at research laboratories, today's hospital-based centers predominantly utilize cyclotrons although synchrotrons are also used. Modern cyclotrons -particularly superconducting ones -offer a number of advantages in terms of simplicity, capital cost and possible dose rate at the patient; 1 Gy may be accurately delivered to a patient by such a source in less than a minute using an average current of <1 nA [9]. However, higher-intensity cyclotrons are typically limited to around 230-250 MeV kinetic energy due to relativistic effects, and their fixedenergy extraction requires the use of a mechanical degrader (typically graphite) to lower the proton energy for shallower proton dose delivery.…”