PSI, Villigen PSI, Switzerland
University of Zurich, University Hospital, Zurich, Switzerland
The COMET cyclotron* at PSI has been successfully used to treat patients with static tumors using the spot scanning technique, i.e. sequentially irradiating different positions inside the tumor volume. Irradiation time for each position ranges from micro- to milliseconds, with total treatment duration of about a minute. For some tumors (e.g. lung) physiological motion (e.g. respiration) interferes with the scanning motion of the beam, lowering treatment quality**. For such mobile tumors, we are developing a new technique called continuous line scanning (CLS), aiming at reducing treatment time by more than 50%. In CLS, dose rate should stabilize (within few percent) within tenths of a millisecond. We thus implemented a first prototype for fast, real-time beam control: a PID controller sets the internal electrostatic vertical deflector of the accelerator, regulating the beam current output based on the instantaneous current measured just before the patient and the knowledge of the transmission from the accelerator to the patient. In pre-clinical experiments, we achieved good control of the global dose delivered; open issues will be tackled in the next version of the controller.
*Schippers, J. M., et al (2007). NUCL INSTRUM METH B, 261(1-2), 773–776.
**Phillips, M. H., et al (1992). PMB 37(1), 223–233.
