Akira Maruhashi

Multi-layer energy filter for realizing conformal irradiation in charged particle therapy

A new type of filter for charged particle radiotherapy is developed to reduce unwanted dose transfer to the normal tissues around a tumor. The new filter can make a static irradiation field where the width of the spread-out Bragg peak (SOBP) is two-dimensionally adjusted. That makes the field conformal to the tumor three-dimensionally. The filter is made of many layers produced by using stereolithography. The layer has a miniaturized structure that has geometrical similarity to the conventional ridge filter. Shapes of cone and pyramid are also usable for the unit-cell constructing the layer. The spread of the field in the depth direction is decided by the thickness of the filter, or by the number of layers. The experimental result of the irradiation using the ridge-type construction shows a good agreement with an estimate by the Monte Carlo calculation. By combining this technique with intensity modulation that has lateral position dependence, the conformal irradiation can be achieved by a simple procedure.

Deterioration of imaging plate by proton irradiation and an evidence of its recovery

Abstract An imaging plate (IP) was excessively irradiated by 250 MeV proton beam up to 4.3×10 13 protons/cm 2 in order to examine the resultant radiation damage. As a function of proton fluence, variations in photo-stimulated luminescence (PSL) signals were evaluated by comparing with the region without previous extensive proton irradiation on the same IP. Notable deterioration of PSL signal was found for the fluence more than 5×10 12 protons/cm 2 . Furthermore, partial recovery of the deterioration was evidently observed, which was promoted by keeping the IP at 50–70°C.

Characteristics of proton beams after field shaping at PMRC.

The proton irradiation control system was developed for cancer radiotherapy at the Proton Medical Research Center, with the extension of a beam line connected to a synchrotron at the High Energy Physics Laboratory. The initial energy of the 500 MeV proton beam supplied by the accelerator is degraded down to 243 MeV after passing through a graphited rod. In the control system, a proton beam is scattered to form a large field, its Bragg peak width is spread out, and its energy is degraded to the optimum value with a range covering tumour depth. The characteristics of the devices required for these procedures have been investigated from the viewpoint of the relationship between dose rate and field flatness, taking the setting-up geometry of these devices into consideration.

Three-dimensional conformal irradiation with a multilayer energy filter for proton therapy

The first experimental evidence of three-dimensional conformal irradiation is performed by using a new type of filter developed for charged particle radiotherapy. The new filter can yield a static irradiation field where the width of the spread-out Bragg peak is adjusted to the target as a two-dimensional continuous function in the transverse plane. The filter is made of many layers produced by using stereolithography. In the filter, a structure with two regions with different shaped miniaturized ridges is adopted to get a flat dose profile on the spread-out peak. A conformal field around a spherical target is realized by a filter that has a shape corresponding to the outward form of the target.

Several problems on the application of PIXE to cancer diagnosis

Abstract Availabilities of PIXE, AAS, ICP and XRF for detecting the trace elements in the biomedical specimens were compared. The sensitivities of PIXE to the several elements including copper and zinc which were analyzed mainly for cancer diagnosis were higher than the other trace element analytical methods. PIXE, however, required more complex handling techniques and longer data acquisition time in comparison with the others. Moreover, the conditions for keeping the high level of reproducibilities were more difficult for PIXE than for the others because of the burning of the sample holder by the incident particles, etc. As a result, a combination of PIXE, ICP(AAS) and XRF was indispensable and very useful for the detection of many sorts of trace elements in biomedical samples. It is desirable that ICP(AAS) and XRF be used for screening for cancer and PIXE for confirming it. Removal of the impurities in the biochemical samples, mainly carbon and chlorine, was achieved through the combined treatment of oxidation using acid solutions, drying at temperature lower than the boiling point and ashing.