[Nationwide Survey of Medical Radiation Exposure on Cardiovascular Examinations in Japan].

PURPOSE: It is very important to manage the radiation dose of cardiovascular interventional (CVI) procedures. Overseas, the diagnostic reference levels for cardiac interventional procedures were established with the air kerma at the patient entrance reference point (Ka,r) and the air kerma-area product (PKA). Although the Japan DRLs 2015 was established by the Japan Network for Research and Information on Medical Exposure (J-RIME), the Japan DRL for CVIs were established by fluoroscopic dose rates of 20 mGy/min at the patient entrance reference point with 20 cm thickness polymethyl methacrylate (PMMA) phantom. In the present our study, we performed a questionnaire survey of indicated values of angiographic parameters in CVI procedures. METHODS: A nationwide questionnaire was sent by post to 765 facilities. Question focused on angiographic technology, exposure parameters and radiation doses as the displayed dosimetric parameters on the angiographic machine. RESULTS: The recovery rate was 22.8% at 175 out of 765 facilities. In total 1728 cases of the coronary angiography (CAG), 1703 cases of the percutaneous coronary intervention (PCI), 962 cases of the radiofrequency catheter ablation (RFCA) and 377 cases of pediatric CVI. The 75th percentile value of Ka,r, PKA, fluoroscopy time (FT) and number of cine images (CI) for CAG, PCI, RFCA and pediatric CVI were 702, 2042, 644, and 159 mGy, respectively, 59.3, 152, 81.3, and 14.9 Gy・cm2, respectively, 10.2, 35.6, 61.1, and 35.6 min, respectively and 1503, 2672, 722, and 2378 images, respectively. Our investigation showed that the angiographic parameters were different in several CVI procedures. CONCLUSIONS: The displayed dosimetric parameters on the angiographic machine in CVI procedures showed different values. We should classify the dosimetric parameters for each procedure.

Derivation of total filtration thickness for diagnostic x-ray source assembly.

The method defined by the IEC 60522 for determining the inherent filtration of an x-ray source device is applicable only for a limited range of tube voltage. Because the users cannot legally remove the x-ray movable diaphragm of the x-ray source device, total filtration, which is the sum of the additional filtration diaphragm movable for specific filtration and x-ray, cannot be measured. We develop a method for simply obtaining the total filtration for different tube voltage values. Total filtration can be estimated from a ratio R' of the air kerma [Formula: see text], which is measured with an Al plate with thickness T, and [Formula: see text] measured without an Al plate. The conditions of the target material of the x-ray source device are then entered into the Report 78 Spectrum Processor to calculate the air kerma K x and K x+T for Al thicknesses x and (x + T), respectively, to obtain R. The minimum value of x, which is the difference between the R and R', is the total filtration of the x-ray source device. The total filtration calculated using the industrial x-ray source device was within ±1% in the 40-120 kV range. This method can calculate the total filtration using air kerma measurements with and without the Al plate. Therefore, the load on the x-ray tube can be reduced, and preparation of multiple Al plates is not necessary. Furthermore, for the 40-120 kV tube voltage range, the user can easily measure the total filtration.

Calibration coefficients of dosimeters used in mammography for various target/filter combinations.

A wide variety of existing combinations of target and filter materials (target/filter combinations) are used in mammography equipment. The patient dose depends on the X-ray quality that is derived from the target/filter combination, and a calibration of the dosimeter that is used in the measurement that corresponds to the specific target/filter combination is necessary. However, dosimeters in mammography are generally calibrated with reference to the X-ray quality of Mo/Mo or W/Al combinations, and it is unclear whether or not the X-ray quality that is derived from other target/filter combinations will affect the calibration coefficients. In this paper, the calibration coefficients of different dosimeters were evaluated for target/filter combinations. For an ionization chamber-type dosimeter, good energy dependence was found and the effect of the target/filter combination was small. However, for a semiconductor dosimeter, a large energy dependence was found, and different calibration coefficients that depended on the target/filter combination used were required.

Calculation of air-kerma rate of diagnostic X-ray generators.

As one type of basic physical data related to the calculation of the construction of X-ray examination room shielding, we investigated the air-kerma rate 1 m from the source of the useful beam focus per unit current time product. Compared to the X-ray energy penetration values obtained in prior research, we obtained higher values. We found three causes for this discrepancy: (1) the X-ray tube total filtration (increasing total filtration reduces air kerma), (2) the tube voltage ripple percentage (increased voltage ripple reduces air kerma, and (3) the target angle (increasing the target angle increases the air kerma). On standardizing (1)-(3), we confirmed that our values mostly matched those obtained in past research. Consequently, when one employs the air-kerma rate that results from the consideration of (1)-(3), without pursuing a path of excessive safety, calculation of shielding under clinical conditions is possible.

[Shielding evaluation of lead-free board for diagnostic X-rays].

For physical foundation data used in the shielding calculation of structural facilities such as a radiation room, there are air kerma transmissions concerning the thickness of shielding objects, and half value layers and tenth value layers concerning a greatly attenuated wide X-ray beam. Accordingly, we evaluated the above-mentioned items with a lead-free board, which is mixed sulfuric acid calcium and barium sulfate with equiponderance for the amount of sulfuric acid calcium included in the usual plasterboard. Permeability in NCRP Report 147 is expressed by 3 parameters, α, ß and γ, and shielding objects x. It showed that it corresponds to the measurement point and permeability curve with parameters, α, ß and γ obtained by nonlinear regression analysis. Furthermore, we calculated the half value layer and tenth value layer concerning the greatly attenuated wide X-ray beam. The evaluated lead-free board, used in this examination, is useful as the shielding material for the diagnosis X-ray and, moreover, the partition wall materials are hard enough, with a board that is even heavier than the usual plaster board. Besides, the use of lead-free materials is friendly to the general environment.

[Evaluation of non-lead board as X-ray protective material].

For security, boards containing lead are commonly used to partition off rooms adjacent to radiation facilities. From the viewpoints of environmental safety and of material recycling during the process of remodeling or repair, however, the trend is toward avoiding the use of lead-containing radiation-protection board. Consequently, we developed a lead-free board(W 910xH 1820xD 12.5 mm)composed of a mixed material incorporating calcium sulfate and barium sulfate to be used as a partition at a diagnostic X-ray institution. The mass attenuation coefficients of the lead-free board were lower by about 12% and 60% for energy ranges of 25 approximately 37 keV and 38 approximately 41 keV, respectively, as compared with those of lead. Lead equivalents for the newly developed board(12.5 mm thickness)were 0.87+/-0.01 mmPb at 100 kV tube voltage, 0.60+/-0.01 at 125 kV, and 0.47+/-0.01 at 150 kV. A double-layer lead-free board proved to have enough shielding ability even at usual photographic frequencies.

[Evaluation of patient entrance dose rate of interventional X-ray equipment].

Because interventional radiology (IVR) procedures are being performed with increasing frequency, patient X-ray exposure dose for X-ray fluoroscopic and radiographic procedures should not be ignored. In order to avoid excessive X-ray exposure, exposure dose rate limits are specified in the Japanese Industrial Standards (JIS) and by civil law at 50 mGy/min for usual fluoroscopy and 125 mGy/min for high-dose fluoroscopy. In the present study, we examined the difference in patient incident dose rate before and after using an X-ray generator that satisfied the above requirements. For incident dose to the image intensifier (I.I.), we investigated the differences between continuous and pulsed fluoroscopy, the effects of additional filters (Ta: tantalum, Al: aluminum), and the form of the X-ray spectrum. For pulsed fluoroscopy using PMMA (polymethyl-methacrylate), the maximum patient incident dose rates of usual and high-dose fluoroscopy were 59 mGy/min and 151 mGy/min, respectively. With regard to I.I. incident dose, saturation was observed beginning at a PMMA of 20 cm, and the X-ray dose was insufficient. In terms of the difference in patient incident dose rate with Ta and Al filters, the dose rate with the Ta filter was approximately 50% lower than that with the Al filter except for the saturation area. Concerning the X-ray spectrum, it was considered that a Ta filter not only minimizes patient X-ray exposure (because Ta reduces soft X-rays more effectively than Al) but also minimizes scattered X-rays because it filters out hard X-rays, leading to improved image quality. However, the use of the filter is appropriate only when a sufficient I.I. incident dose can be ensured. Specifically, the use of the filter under saturation conditions can lead to deterioration in image quality. Therefore, IVR X-ray systems must be equipped with an appropriate filter for reducing X-ray exposure while maintaining a sufficient I.I. incident dose rate.

Use of instrumental neutron activation analysis to determine concentrations of multiple trace elements in human organs.

AInasmuch as the availability of suitable analytical specimens may be limited, the defining of normal concentrations or ranges of trace elements in human organs is problematic. Little is known about whether various parts of an organ, or of bilateral organs, differ in their concentrations of trace elements. In this study, the authors determined the distribution of trace elements in different portions of human organs, and between the right and left lung and kidney, with instrumental neutron activation analysis (INAA). By setting the variance limit at less than 20%, they determined that trace elements were similar in 7 of the 9 organs tested (the exceptions being kidney and lung). Trace element concentrations found in the right lung were very different from those found in the left lung. Some trace elements varied in concentration according to the part or laterality of the organ tested.

Determination of multielement concentrations in normal human organs from the Japanese.

In order to elucidate the distribution of elements in organs from healthy Japanese, instrumental neutron activation analysis (INAA), based on the preliminary examination, was applied to quantitative determination of multielements in nine organs autopsied (brain, heart, kidney, liver, lung, muscle, pancreas, spleen, and thyroid). The following results were obtained: (1) The values obtained for each element could be considered to be representative as "normal values" and "ranges" in organs from healthy Japanese males; (2) the essential elements Br, Cl, Co, Cu, Fe, K, Mn, Na, Rb, Se, and Zn were not affected by external environmental factors or by racial difference; (3) renal and hepatic Cd levels were very high in several cases and the accumulation has still been in progress in the Japanese, whereas the contaminant elements are low in each organ except for lung.