Synchrotrons for hadron therapy: Part I

The treatment of cancer with accelerator beams has a long history with beta trons, linacs, cyclotrons and now synchrotrons being exploited for this pur pose. Treatment techniques can be broadly divided into the use of spread-ou t beams and scanned 'pencil' beams. The Bragg-peak behaviour of hadrons mak es them ideal candidates for the latter. The combination of precisely focus ed 'pencil' beams with controllable penetration (Bragg peak) and high, radi o-biological efficiency (light ions) opens the way to treating the more awk ward tumours that are radio-resistant, complex in shape and lodged against critical organs. To accelerate light ions (probably carbon) with pulse-to-p ulse energy variation, a synchrotron is the natural choice. The beam scanni ng system is controlled via an on-line measurement of the particle flux ent ering the patient and, for this reason, the beam spill must be extended in time (seconds) by a slow-extraction scheme. The quality of the dose intensi ty profile ultimately depends on the uniformity of the beam spill. This is the greatest challenge for the synchrotron, since slow-extraction schemes a re notoriously sensitive. This paper reviews the extraction techniques, des cribes methods for smoothing the beam spill and outlines the implications f or the extraction line and beam delivery system (C) 1999 Elsevier Science B .V. All rights reserved.