Biophysical characteristics of HIMAC clinical irradiation system for heavy-ion radiation therapy.

PURPOSE: The irradiation system and biophysical characteristics of carbon beams are examined regarding radiation therapy. METHODS AND MATERIALS: An irradiation system was developed for heavy-ion radiotherapy. Wobbler magnets and a scatterer were used for flattening the radiation field. A patient-positioning system using X ray and image intensifiers was also installed in the irradiation system. The depth-dose distributions of the carbon beams were modified to make a spread-out Bragg peak, which was designed based on the biophysical characteristics of monoenergetic beams. A dosimetry system for heavy-ion radiotherapy was established to deliver heavy-ion doses safely to the patients according to the treatment planning. A carbon beam of 80 keV/microm in the spread-out Bragg peak was found to be equivalent in biological responses to the neutron beam that is produced at cyclotron facility in National Institute Radiological Sciences (NIRS) by bombarding 30-MeV deuteron beam on beryllium target. The fractionation schedule of the NIRS neutron therapy was adapted for the first clinical trials using carbon beams. RESULTS: Carbon beams, 290, 350, and 400 MeV/u, were used for a clinical trial from June of 1994. Over 300 patients have already been treated by this irradiation system by the end of 1997.

Elemental distribution in frozen-hydrated mouse lenses with hereditary cataract.

Nakano mice (nct/nct) and its congenic strain (Balb/c-nct/nct) develop different types of cataract: the former develop intense nuclear cataract but the latter develop milder opacity at the cortical region of lenses more later in life. The present study was undertaken to compare the elemental compositions at the localized region of these lenses in order to examine the possible role of ions in the opacification of the hereditary cataracts. Eight lenses from Nakano mice (age: 39-40 days) and ten lenses from congenic mice (age: 73 days) were prepared for the X-ray analysis with a high energy ion microprobe at a resolution of 50 microns. The age of mice was two weeks after 50% cataract formation for the respective strain. The maps of the concentrations of S, Cl, K and Ca in the central planes of the frozen-hydrated lenses were obtained. In all of the congenic lenses analyzed, the normal elemental composition, low Cl and Ca, and high K, was retained only in the narrow anterial and equatorial peripheral region and the other region underwent a K loss with a gain of Cl and Ca. In the Nakano lenses, the altered elemental composition was localized in central and in posterial cortical regions. There was no distinct difference in the concentration levels of Cl, K and Ca in the central region of the lenses between the two strains. The level of S was lower in Nakano lenses. High calcium containing spots were detected in low K regions of some of the lenses examined.

Biochemical evidence for conversion to milder form of hereditary mouse cataract by different genetic background.

Congenic hereditary cataract mice, BALB/c-nct/nct, were established by introducing the nct gene from Nakano into BALB/c mice. These mice developed a milder cortical form of cataract which developed sporadically and later in life than in Nakano mice. Combined use of BALB/c and BALB/c-nct/nct mice enables biochemical comparison of normal clear lenses, congenic clear lenses which are destined to be opacified some time later, and opacified lenses in the same genetic and aging statuses. We compared the age-related changes in water content and water-soluble and -insoluble fractions among these three types of lenses. Congenic clear lenses and opaque lenses were more similar to BALB/c normal clear lenses and Nakano opaque ones, respectively, in these parameters. These results suggest, in addition to formation of aggregated crystallins and their accumulation in water-insoluble fractions, that decreased protein synthesis, increased protein degradation and augmented leakage of crystallin might have a significant role in the nct-induced lens opacification.

Elemental distribution in frozen-hydrated rat lenses with galactose cataract.

The elemental distributions in frozen-hydrated rat lenses with galactose cataract were compared before and after the onset of the nuclear cataract to investigate the possible role of ion levels in the lens opacification due to the phase separation of the lens cytoplasm. The maps of the weight concentrations of the minor elements, S, Cl, K and Ca, on the basis of wet weight in the central plane of lens were obtained by X-ray analysis with the high energy ion microprobe at a resolution of 50 microns. Before the onset of the nuclear cataract, the distributions of Cl and K, were almost normal, except in the lens posterior periphery with high Cl and low K. In the lens with the nuclear opacity, sudden changes were observed. The Cl increased throughout the lens, and K decreased throughout the lens except at lens anterior thin layer. However, the totalized monovalent ion level changed only slightly. The Ca level increased throughout the lens after the onset of the nuclear cataract, suggesting a possible role of Ca in the nuclear opacification of galactose cataract of rats. The distributions of S were similar to the protein density distributions previously known both in the normal and in the cataractous lenses.

Proton computed tomography applied to small biomedical samples.

The computed tomography (CT) using the high-energy proton beam has the potential advantage of superior density resolution in the soft tissue analysis as compared to the conventional X-ray CT.We have developed the "first generation" type proton CT system using a 25-MeV proton beam to study the density distributions in small biomedical samples (<6 mm ϕ).The specimens were fixed in a cylindrical sample holder that was immersed in a water bath. The sample holder was scanned in front of the external semimicro beam of protons with a width of 0.06 mm at full width of half maximum (FWHM). The residual energy of the penetrated proton beam was analyzed with a solid state detector (SSD). The obtained integral density projection views were reconstructed into the density image by the filtered back projection method using the Shepp-Logan filter function.The spatial resolution of 0.1 mm and the density resolution of 0.1% were obtained by our system.The technique was applied to the eyes of small animals to study the changes in the density distributions of lenses, which develop with lens opacification in cataracts.