A white-beam fast-shutter for microbeam radiation therapy at the ESRF

The ID17 Medical Beamline port at the European Synchrotron Radiation Facility (ESRF) delivers white beam generated by a 1.4 T wiggler. It is devoted to medical applications of synchrotron radiation. One major program of the beamline is called Microbeam Radiation Therapy (MRT). In this radiotherapy technique, still under development, the white beam fan is divided into several microbeams before reaching the target which is a tumoral brain. The maximum skin-entrance absorbed dose can reach extremely high values (over 1000 Gy) before causing tissue necrosis, while causing tumor necrosis. One of the key parameters for the success of the MRT is the accurate control of the radiation dose delivered to the target, as well as its location with respect to the tumor, to prevent unnecessary damage to normal tissues. Therefore, the opening and closing positions of the shutter while the target is moving vertically at a constant speed reaching 150 mm/s must be carefully controlled. Shutter opening times as short as 5±0.5 ms must be achieved. The total power of the white beam generated by the wiggler may reach 14.5 kW. It is essential to maintain vacuum continuity in the entire beamline and therefore the shutter had to be built to be vacuum compatible to a level of 10−8 mbar. This paper describes the fast shutter mechanics and its associated electronics.