‘Riesenrad’ ion gantry for hadrontherapy: Part III

When using accelerator beams for cancer therapy, the three-dimensional freedom afforded by a gantry helps the treatment planner to spread out surface doses, avoid directions that intercept vital organs and irradiate a volume that is conformal with the tumour. The general preference is for an iso-centric gantry turning 360° in the vertical plane around the patient bed with sufficient space to be able to orientate the patient through 360° in the horizontal plane. For hadrontherapy, gantries are impressive structures of the order of 10 m in diameter and 100 ton in weight and to date only proton gantries have been demonstrated to operate satisfactorily. The increased magnetic rigidity of say carbon ions will make ion gantries more difficult and costly to build. For this reason, exo-centric gantries and, in particular the so-called ‘Riesenrad’ gantry with a single 90° bending magnet, merit further attention. The power consumption is reduced and the heavy magnets with their counterbalance weight are reduced and are kept close to the axis. The treatment room, which is lighter, is positioned at a larger radius, but only the patient bed requires careful alignment. An optics module called a ‘rotator’ is needed to match an incoming dispersion vector to the gantry in order to have an achromatic beam at the patient. A practical design is described that assumes the beam is derived from a slow-extraction scheme in a synchrotron and that the beam sizes are controlled by modules in the transfer line. Magnetic scanning is integrated into the gantry optics for both transverse directions.     

Evaluation of annular pupil for scanning transmission electron microscope formed by focused ion beam technique

Annular pupils for electron optics were developed using a focused ion beam (FIB) technique to realize an increase in the depth of focus, aberration-free imaging and separation of amplitude and phase images under scanning transmission electron microscopy (STEM). A tantalum plate 30 μm thick was used as the annular pupil material in the present experiment. The annular pupils were designed with various outer diameters from ?120 μm to ?40 μm. The inner diameter was designed at 60 to 80% of the outer diameter. The fabricated annular pupils were inspected by scanning ion beam microscopy and scanning electron microscopy. Annular pupils were successfully obtained at the designed size, although the slits of the pupils were slightly tapered by the ion beam etching process. These annular pupils were loaded on a STEM and confirmed to display no charge-up phenomenon by observation of the projection image on a scintillator using a CCD camera. We confirmed the image taken by annular pupil with narrow width was able to suppress the influence of the normal illumination.     

ACOLISSA: a powerful set-up for ion beam analysis of surfaces and multilayer structures

The experimental set-up for analysis of the charge of light ions scattered from surface atoms (ACOLISSA) is described in the following paper. ACOLISSA is used for determination of flight times of low-energy ions. It permits time-of-flight low energy ion scattering spectra of all scattered projectiles (TOF-LEIS-AP) as well as charge separated (TOF-LEIS-CS) spectra to be recorded. The evaluation of TOF-LEIS-AP spectra allows subsurface layers of the target to be studied. The analysis of TOF-LEIS-CS spectra together with ions only spectra (TOF-LEIS-IO) is used for investigation of the neutralization behaviour of projectiles at the outermost atomic layer. The performance of the set-up is described and, as an example, spectra are shown for a polycrystalline Cu target and a 7 Å Cu layer deposited on top of an alumina substrate.