The backscatter factor is necessary for evaluating the skin dose of patients irradiated by diagnostic x-rays. In this study, backscatter factors for x-rays of various irradiation conditions were calculated by means of the Monte Carlo method. The backscatter factors calculated for X-rays, which had the same HVL but different tube potentials, did not always coincide with each other. From this result, it was evidenced that the backscatter factor obtained from the BSF data table with a parameter of HVL were uncertain. To avoid such uncertainties, a new convolution method to obtain backscatter factors using an x-ray spectrum and differential backscatter factors was developed. This new calculation method could be installed in a computer program with an approximating equation of x-ray spectra, and accurate backscatter factors for any x-ray and/or any irradiation field could be obtained easily.
The mean mammary gland dose, which is used as an index of the dose of exposure to radiation in mammography, is obtained by multiplying the in-air exposure on the entrance surface by the absorbed dose conversion factor. Sobol et al. reported a method of calculating the absorbed dose conversion factor that is determined by x-ray quality(tube voltage and half-value layer), compressed dreast thickness, and breast composition. A method of calculating mean mammary gland dose, however, has not been established, and no software for estimation of the dose of exposure to radiation in mammography has been developed. Recently, the authors developed software for the estimation of exposure dose that can be easily used in a facility without a dosimeter. They confirmed that the use of this new software enabled the calculation of meanmammary gland dose based on the mammary gland ratio. In a facility without measurement equipment such as a dosimeter, a user can estimate the exposure dose without difficulty simply by entering the exposure conditions. Furthermore, half-value layer, in-air exposure, and conversion factor can be calculated by using the newly developed software. This technique seemed to be sufficienlty useful if a user simply estimates'exposure dose.
We propose a new equation to estimate patient surface absorbed dose from effective x-ray energy. The equation is represented as follows : D(skin absorbed dose)=Ds×mAs×FSF×F×DST, where Ds indicates basic exposure, mAs is additional x-ray tube current and exposure time, FSF is a factor used to count additional scattered exposure, F is a conversion coefficient to convert from exposure to absorbed dose, and DST is distance compensation. For Ds, the value of the exposure dose without aluminum in the half-value layer(HVL)measurement for 1 mAs was used(C/kg/mAs). FSF is a ratio of exposure containing scattered radiation that corresponds to field size to basic exposure. F was calculated using reported values of attenuation coefficients in the data book. Then approximation function curves for Ds, FSF, and F were success-fully created, with an excellent correlation coefficient(R^2=0.997), using effective x-ray energy as a variable.
The computed radiography system has been changed by the film-screen system, and x-ray equipment has been changed by the inverter type, which is more stable than the conventional type. However, effective energy and dose differ among the various types of equipment. In this study, we examined the relation of effective energy and dose to tube voltage, in four types of inverter-type x-ray equipment. The relation between effective energy and tube voltage was a quadratic curve. No correlation was found between tube voltage and effective energy, or total filtration. Moreover, although the linearity of the relation between effective energy and dose was good, inclination differed slightly. That is, when a radiograph was taken under the same conditions in each radiography room, dose changed remarkably according to the type of equipment. By correcting for radiation quality and mAs value, it will be possible to standardize patient exposure dose, and quantification of exposure and image quality can be achieved.
Interventional radiology(IVR)procedures may involve high radiation doses that are potentially harmful to the patient. In IVR procedures. pulsed fluoroscopy can greatly decrease the radiation that the physician and patient receive. There are two types of pulsed fluoroscopy : direct control and primary(indirect)control. The purpose of this study was to compare pulsed fluoroscopy by direct control, using a grid-controlled x-ray tube, with pulsed fluoroscopy using primary control. For both types of pulsed fluoroscopy, we measured the waveforms(x-ray tube voltage, x-ray tube current, and x-ray output)and the relative radiation dose. In addition, we compared the decrease in radiation during pulsed fluoroscopy using a care filter. The studies were performed using a Siemens Bicor Plus x-ray System(direct control)and a Siemens Multistar Plus x-ray System(primary control). Using primary pulse control, a 50% decrease in the x-ray output waveform took approximately 0.5-1.0 msec, or longer with a lower x-ray tube current. Using direct pulse control, a 50% decrease in the x-ray output waveform took approximately 0.1 msec, and was independent of x-ray tube current. The rate of radiation reduction with primary pulse control using the care filter with a lower x-ray tube current had a slope exceeding 10%. Pulsed fluoroscopy by direct control using a grid-controlled x-ray tube permits an optimal radiation dose. To decrease the radiation in primary pulse control, a care filter must be used, particularly with a lower x-ray tube current.
Among the basic characteristics of the dose area product meter, the following were examined : effect of the heel effect which derives from hardening, atmospheric correction coefficient, response of measuring plane of the DAP meter, target focus angle of an x-ray tube assembly of quality of radiation by the area dosimeter mounting, and conversion from the value of the area dosage to air kerma. In terms of tube voltage, the IEC standard is almost always observed, if the radiation field in the dosimeter's surface area is within 6cm×6cm. Error was 17.6%, even if all factors were not considered, and even if the conversion to air kerma was possible. It was indicated that the conversion to air kerma in the patient was possible when the radiation field and measurement error in the dosimeter's surface were considered.
Purpose : To estimate scattered dose rates from phantom measurements during interventional radiology(IVR)and to establish methods to reduce the angiographer's exposure in IVR. Materials and methods : Scattered dose rates were measured in lines parallel in space to the central ray of the x-ray beam, at lateral distances of 50 cm. They were measured by the ionization chamber dosimeter, which was made to have directivity by a lead slit. New radiation protective devices for angiographers were developed and their effects evaluated. Results : The scattered dose rates to which the angiographer was exposed during IVR were scattered from a collimator and a patient. The abdominal area was almost completely exposed by the scattered dose from the patient. The head and neck area were exposed by the commensurate scattered dose from the collimator and the patient. The scatter exposure rates of the abdominal area were reduced to 5-20% by a lead curtain attached beneath the tissue table and a lead barrier next to the patient's trunk. And the scattered dose rates of the head and neck area were reduced to 50-70% by shielding a surface of the tissue table between the angiographer and the patient. Conclusion : To reduce exposure of the head and neck area, it is necessary to shield the surface of the tissue table between the angiographer and the patient. To reduce exposure of the abdominal area, it is necessary to shield beneath the tissue table and next to the patient's trunk. The new radiation protective devices were considered very useful and effective in reducing the angiographer's exposure rates.
The method for obtaining patient skin dose by measuring the air kerma in the patient's skin surface is being recommended. Back Scatter factors(BSF)that correspond to the radiation field in the patient's skin surface and the quality of the x-ray are necessary at that time. Although the backscattering coefficient published in Supplement 17 of the British Journal of Radiology has been widely used, there are some problems and human tests are necessary, Because it is difficult to measure BSF in each of the human internal organs and body tissues for patient skin dose, the backscattering coefficient was obtained using the Monte Carlo calculation code, and its usefulness was examined by comparing the results with the measured values of the TLD element. The results with EGS4 Monte Carlo code were similar to the results measured using TLDs. Therefore, we consider it effective in the x-ray equipment and under the experimental conditions that were used for this method. However, the values that we obtained were 4-7% lower than those of Supplement 17, IPSM, and AAPM. It will be necessary to examine them including characteristics of the x-ray generators such as the x-ray spectrum.
Because HSG is an x-ray examination for the genital glands, it is very important to reduce x-ray exposure to the patient. However, reducing exposure decreases image quality and causes a lack of optimization in image quality and dose. In computed radiography, image density does not depend on the dose exposed, and appropriate images can be obtained by adjusting the image processing parameters. Therefore, computed radiography can reduce x-ray exposure and improve image quality. In this study, we performed HSG using low-dose radiography with computed radiography(CR)systems and evaluated a simple procedure for reducing exposure dose while maintaining image contrast by changing radiation quality and adding filters. We also examined ways to reduce dose by using both procedures. We found that low-dose radiography using the CR system could increase the S value to 1, 200 from visual evaluation and could reduce by patient skin dose by 58%. To maintain the image contrast by changing radiation quality, the radiographic condition that was the same as 80 kV without the filter was a 72kV tube voltage with 0.3mm copper and 1 mmaluminum filter, and it could reduce patient skin dose by 57%. In HSG examination, Patient skin dose could be reduced by 82% by low-dose x-ray radiography using a CR system and by adding a filter, and it could offer images that showed no loss of diagnostic quality. Therefore, it could be said that our procedure for HSG is useful for the optimization of image quality and dose.
A calculation method was devised to measure the amount of radiation exposure a patient receives during PTCA. The objective was to develop a plan to decrease exposure and help prevent the occurrence of any problems. Of 200 cases of coronary angiography studied, the average amount of radiation absorbed in the skin during angiography and fluoroscopy was calculated to be 2, 028 mGy, with temporary redness on the skin. However, locally no overlapping skin area exceeded 2, 000 mGy. The amount of radiation absorbed through the skin can be calculated during a procedure. As a result, during PTCA the operator will try to keep the patient's best interest in mind by making sure procedures are fast, simple, and safe by shortening cine and fluoroscopy time.