[en] Assessment was made of the three-dimensional dose distribution of open-field (O-F) beams in 54 patients with breast cancer treated by tangential breast irradiation (TBI). A new irradiation technique was developed for attaining optimum dose distribution of TBI. The treatment planning for the TBI was performed using a CT-simulator. Dose distribution was by the modified equivalent tissue maximum ratio method and normalized with respect to isocenter CT slices. For O-F beams, dose homogeneity was found to be determined by the anatomy of breast, tissue depth on central beam axis and length of the lung included in a tangential field. When tissue depth was greater than 11 cm, a 'hot spot' in excess of 110% of the isocenter dose could always be detected on the lateral chest wall, sternum, and near the apex of the breast. The area dose of a 'hot spot' increased by the SINGLE-WEDGE-FIELD irradiation technique using a single-wedge filter for tangential beams, but decreased by the TWIN-WEDGE-FIELD (T-W-F) irradiation technique when using a twin-wedge filter. The present technique concluded the best method for treating TBI in breast cancer patients. (author)

[en] The data table of a 1 cm dose equivalent per fluence to estimate the effective dose equivalents conservatively from external photon beams were given by ICRP. However, these data were calculated with single energy photon beams; therefore, it must be careful when for applying the data to photon beams with spectral distributions. In this paper, we calculated the 1 cm dose equivalent per unit exposure for spectral photon beams by means of a Monte Carlo simulation, and ascertained the suitability of the usual method which estimates dose equivalents by means of ICRP data corresponding to the effective energy of the spectral beam. Consequently, the 1 cm dose equivalent per unit exposure calculated for primary X-ray beams and for scattered photon beams from an irradiated body were in good agreement with the ICRP data corresponding to the effective energies of each beam. However, those calculated for X-rays transmitted through a lead shield showed a considerably lower value than ICRP data corresponding to their effective energies. (author)

[en] The FEDIF method in MR imaging has been examined: In particular, the use of low flip angles for enhancing the cervical spinal cord and breath-holding practice for the abdomen. The experimental parameters such as the flip angle and TR in the FEDIF method were determined by measuring the MR intensity for white matter, gray matter and cerebrospinal fluid in human brain, and fat in temporal region. Based on these data, the flip angle clinically suitable for MR imaging of cervical spinal cord and abdomen were determined from the measurement of object contrast and S/N as well as a visual inspection. Due to the smaller motion artifacts present in the FEDIF method with 8deg flip angle than the long SE method, the former is clinically more advantageous than the latter to obtain the enhancement of cerebrospinal fluid. The imaging with breath-holding in abdomen produced distinctly clear images. The contrast between different tissues can be varied by flip angle, and thus, a region of interest is clearly seen. The above result can lead to the conclusion that the FEDIF method is extremely suitable for obtaining distinct images from the abdomen and cervical spinal cord in a shorter time than other MR imaging method. (author)

No abstract available

[en] The Monte Carlo computer program has been used to analyze the characteristics of scattered radiation in a phantom irradiated by 10 MV X-rays. The program simulated an irradiation by 10 MV X-rays with a 0 area field upon a center of 30 x 30 x 30 cm³ water phantom. The study distinguished energy distribution of the secondary electron which was set in motion by interactions in the ring with radius R and depth d. Using these results, spectrums of the secondary electron on the beam axis of the circular fields were calculated by means of the superposition principle. Ratios of the average collision mass restricted stopping power (water/air, acrylic/air, polystyrene/air) on the beam axis of circular fields were calculated based on the electron spectrum data. Stopping power ratios calculated on spectrum of electron, which were set in motion only by first interactions of the primary photon beam, coincided with the data in AAPM protocol (1983) within 0.5 %. However, stopping power ratios, which were calculated on electron spectrums with full interaction, increased with the field radius, and differed from AAPM data beyond 2 % at the maximum. For precise measurement or calculation of the absorbed dose for high energy radiation, it is better to apply the mass restricted stopping power ratios based on the electron spectrum with full interactions. (author)

[en] At present, a large number of SPECT systems are being widely used in Japan, hence, it is reasonable for us to know the physical and imaging characteristics of these SPECT devices, and also to recommend the optimum utility of SPECT systems. For this reason, a survey respect of characteristics of the commercialy available SPECT devices was carried out. In addition to this, various factors which have significant influence over SPECT image quality, such as, data acquisition matrix, reconstruction filter, γ-ray attenuation correction and daily quality control procedure, were also investigated. The materials used for this study are PET/SPECT phantom, Alderson liver phantom filled with Tc-99m solution, and either LFOV-E or ZLC-7500 interfaced to Scintipac 2400 minicomputer with 256 K byte of memory. Following are the results of this study. 1) The suitable data acquisition procedure was 128 x 128 matrix for linear sampling and approximately 64 views for angular sampling. 2) Reconstructed image using pre-processing filter with Wiener and Butterworth filters provided high quality image as compared with the Ramp filter. 3) Weighted backprojection method (WBP) proposed by Tanaka was superior to other methods, such as Sorenson method and Chang method in the object with non-uniform distribution of radionuclide. 4) It was found that uniformity correction of gamma camera and precise adjustment of the center of rotation are most important to maintain the images with a high quality. (author)

[en] Underexposed badge film contains a minor quantity of silver which corresponds to the low radiation dose even after completion of the photographic densitometry ; however, it cannot be detected with a photographic densitometer. We intended to clarify the minor silver content based on radioactivation analysis with thermal neutrons at KUR (Kyoto University Research Reactor). The natural silver consists of two stable nuclides, i.e., ¹⁰⁷Ag and ¹⁰⁹Ag. These can be activated with irradiation of thermal neutrons to two radionuclides, i.e., ¹⁰⁸Ag and ¹¹⁰Ag. In this paper, through the activation analysis of an underexposed badge film, methods of measurements are shown regarding both ¹⁰⁸Ag produced by the ¹⁰⁷Ag (n, γ) reaction and ¹¹⁰Ag by the ¹⁰⁹Ag (n, γ). After underexposed badge films were irradiated with thermal neutrons, some gamma-rays emitted from the radionuclides in the activated films were measured with a high pure Ge detector or a NaI (Tl) scintillation detector. The following results were obtained: (1) several elements such as silver, iodine, gold, antimony, manganese and copper were detected by activation analyses of films exposed to low level ⁶⁰Co gamma-rays, (2) the exposure vs ¹⁰⁸Ag or ¹¹⁰Ag activity curve was linear in the lower dose range of ⁶⁰Co gamma-rays. These data indicate that low level radiation doses, which is indeterminable by ordinary photographic densitometry, can be estimated by activation analysis of silver atoms in badge films. (author)

[en] Risk of mammography should be evaluated by the totally absorbed dose into the mammary gland, which is the point of origination of mammary carcinoma. Using a minute anthracene detector immersed in an alcohol/water mixture, the gland dose was obtained and represented against beam quality (first half-value layer in aluminum) so that it can be presumed from in-air exposure required per view. This study reveals that even if the beam quality of the entrance x-rays is equal for the molybdenum and tungstenum anode x-ray tubes, this does not hold true at each depth of the breasts. The gland dose is around 1/5, for film mammography of the in-air exposure, and is less dependent on age and beam quality compared to skin dose. These results support the use of mammography even for periodic mammary surveys, and also imply that high-sensitivity imaging systems are called for rather than attempting to reduce patient dose by relying on harder beam technique. (author)

[en] Build-down effects in water equivalent phantoms and depth dose curves in inhomogeneous phantoms were measured with thermoluminecent dosimeters (TLDs). The kind of TLDs was CaSO₄ : Tm foil type, and its thickness and diameter were 0.06 mm and 8 mm, respectively. As a result, minute changes in the depth dose in inhomogeneous phantoms were evaluated, and the exit plane was more than the entrance plane for the surface dose. We obtained identical same clinical results in radiotherapy in which the skin reaction was harder on the exit plane. (author)

[en] Recently, digital subtraction angiography (DSA) is seeing widespread use. Especially, intraarterial DSA (IA-DSA) makes good use of interventional radiology. However, we know that the skin dose for DSA is so much larger than general angiography, and halations often appearing on DSA images. In this report, we show two improvements of DSA. First, the skin dose for DSA is successfully decreased to one-sixth compared with the late DSA of cerebral artery by a reduction in acquisition images. Secondly, we are doing well in suppressing halation by exchanging the control point of automatic exposure control (AEC) from one-half to one-fourth. (author)