Applications of Accelerators and Detectors to Cancer Treatment

Abstract:

Given the present availability of high-gradient accelerator technology for compact and cost-effective electron linacs in the 100-200 MeV energy range, the interest for Very High Energy Electron (VHEE) radiotherapy (RT) for cancer treatment recently reached an all-time high. Particular significance is assumed by the Ultra-High Dose Rate (UHDR) regime where the so-called FLASH biological effect takes place, in which cancer cells are damaged while healthy tissue is largely spared. VHEE beams from linacs are especially well adapted for FLASH RT, given their penetration depth and the high beam current needed to treat large deep-seated tumours. In recent years, several multidisciplinary user groups carried out a number of studies on VHEE and FLASH RT issues using the CERN Linear Accelerator for Research (CLEAR) user facility, in close collaboration with the local operation team. In this paper, we give an overview of such activities and describe the main results of chemical and biological tests aimed at clarifying the damage mechanisms at the root of the FLASH effect and the relevant beam parameters needed to achieve it. We also describe the dedicated systems and methods developed and used in CLEAR for these activities, focusing on recent advances in the crucial aspects of uniform beam delivery and high dose rate real-time dosimetry.

Abstract:

VHEE (Very High Energy Electron) therapy can be superior to conventional radiotherapy for the treatment of deep seated tumours, whilst not necessarily requiring the space and cost of proton or heavy ion facilities. Developments in high gradient RF technology have allowed electrons to be accelerated to VHEE energies in a compact space, meaning that treatment could be possible with a shorter linac. A crucial component of VHEE treatment is the transfer of the beam from accelerator to patient. This is required to magnify the beam to cover the transverse extent of the tumour, whilst ensuring a uniform beam distribution. Two principle methodologies for the design of a compact transfer line are presented. The first of these is based upon a quadrupole lattice and optical magnification of beam size. A minimisation algorithm is used to enforce certain criteria on the beam distribution at the patient, defining the lattice through an automated routine. Separately, a dual scattering-foil based system is also presented, which uses similar algorithms for the optimisation of the foil geometry in order to achieve the desired beam shape at the patient location.