Method of calculating percentage depth dose for diagnostic X-rays

Data on the percentage depth-dose of diagnostic X-rays are important in evaluating patient dose from medical exposure. We developed a new method of calculating central-axis depth-dose in a homogeneous tissue phantom irradiated by diagnostic X-rays. First, primary and scattered components of percentage depth-dose for mono-energetic X-rays were calculated by means of Monte Carlo simulation, and the data were stored in data tables. Then, percentage depth-doses for individual X-rays were calculated by making use of the data tables, the photon spectrum of X-rays, and exposure conditions such as field size. This method, which can calculate depth-dose under any condition of irradiation by combining with the approximating equation of the X-ray spectrum, is useful in evaluating the percentage depth-dose of diagnostic X-rays.     

Differential dose albedo for high-energy X-rays on concrete slab

We computed the differential dose albedo (alpha(D)) for high-energy X-rays on a concrete slab when the incident angle, reflection angle, and azimuth angle were changed, by means of Monte Carlo simulation. We found that alpha(D) changed with incident, reflection, and azimuth angles to the concrete slab. On the whole, the larger the incident angle, the larger alpha(D) tended to become. If the incident angle and reflection angle were the same, the larger the azimuth angle, the smaller alpha(D) tended to become. When the incident, reflection, and azimuth angles were the same, the smaller the X-ray energy was, the larger alpha(D) became, in the order of 10 MV, 6 MV, and 4 MV X-rays.     

Pregnancy and diagnostic X-rays

Diagnostic X-ray examinations are carried out in pregnant patients in clinical practice either accidentally or because of clinical urgency. In these cases, estimation of the risk to the conceptus is of paramount importance. The risk is dependent on the gestational age and the amount of radiation dose absorbed by the conceptus. Under normal operating conditions, conceptus doses from extra-abdominal examinations are lower than 1 mGy. In the case of examinations involving the abdomen or pelvis, doses to the embryo may be considerably higher in comparison with extra-abdominal examinations. In such cases, detailed assessment of dose to the conceptus is necessary. Doses to the unborn child below 100 mGy should not be considered a reason for termination of pregnancy. Counselling the pregnant patient regarding the risks of the diagnostic X-ray examination is essential. Deterministic effects have a threshold of 100 mGy or higher. This dose is higher than that expected from the overwhelming majority of the diagnostic X-ray examinations. As a result of radiation exposure, the conceptus is assumed to be at risk for stochastic effects, mainly childhood cancer, leukaemia and hereditary effects. The risk for radiation-induced childhood fatal cancer is about 6% per Gy. Risk estimates for genetic effects have been estimated to be about 1% per Gy. Pregnant workers are also exposed to diagnostic X-rays. The protection provided for the conceptus of the worker should be comparable to that of the general public (1 mGy) during the declared pregnancy. A radiation protection program for pregnant staff working at diagnostic radiology departments should be implemented to control conceptus exposure and assist the pregnant woman in obtaining the information necessary to continue her job safely.     

医用诊断X射线的衰减与防护研究

目的 计算和测量医用诊断X射线与物质相互作用的能量及强度变化规律,研究其防护措施.方法 根据X射线变化规律,计算直射线、散射线与透射线的能谱分布,分析并实验测量不同物质对X射线的屏蔽效果.结果X射线经物质衰减后,强度变低,平均能量提高,能谱变窄;散射线能量和强度都小于直射线.不同物质对X射线屏蔽效果不同.结论 铅是防护医用诊断X射线的理想材料.     

Air kerma transmission factors of Scattered X-rays in the maze of a Linac room for lead shield

Spectra of scattered X-rays in the maze of a Linac (X-ray energies of 4, 6, and 10 MV) room were estimated by means of the Monte Carlo simulation, and air kerma transmission factors of the X-rays scattered through a lead shield were evaluated based on those spectra. Spectra of scattered X-rays showed a maximum in the energy area below 200 keV. The higher the accelerated electron energy, also, the smaller the scattering angle that tended to spread to the higher energy area of the distribution of spectra. The air kerma transmission factor of 120 degrees scattered X-rays of 4 MV X-rays obtained in this study was larger than the transmission factors of 124 degrees scattered photons of (60)Co gamma rays through a lead shield given in ICRP. The air kerma transmission factors of 120 degrees scattered X-rays of 6 MV X-rays were smaller than the transmission factors of 90 degrees scattered photons of (60)Co gamma rays. The air kerma transmission factors of 120 degrees scattered X-rays of 10 MV X-rays was slightly larger than transmission factors of 90 degrees scattered photons of (60)Co gamma rays. Therefore, in the case of a 4 MV X-ray Linac room, the calculation method given in the "Manual of Practical Shield Calculation of Radiation Facilities (2000)" causes underestimation of leakage doses.     

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, β and γ, and shielding objects x. It showed that it corresponds to the measurement point and permeability curve with parameters, α, β 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.     

A novel X-ray transmission ionization chamber dosemeter for patient dose measurements in diagnostic radiology

This paper describes an X-ray transmission ionization chamber diagnostic dosemeter for patient dose measurements and control. The chamber uses a commercially available radiofrequency screen as the wall material in a parallel-plate configuration. A digital varactor bridge electrometer serves to measure air kerma times area of fluoroscopic and radiographic beams. Detailed investigations on the characteristics of the chamber such as saturation, sensitivity, energy dependence (50-150 kV), response versus radiation field area, uniformity of response of the chamber, effects of distance and long-term stability have been carried out. The results demonstrate that the chamber meets all the requirements and can measure the incident patient dose with an overall uncertainty of +/- 11%. The chamber can be either mounted on the housing of the light beam diaphragm of the X-ray unit or used as a stand-alone system along with an image-intensifier TV monitor. It is inexpensive to build and is recommended particularly for hospitals in developing countries.     

Method of calculating side scatter factor for diagnostic X-rays

When computing the amount of leakage from a diagnostic X-ray room, the amount of scattered radiation released from the irradiated body in the lateral direction must be evaluated correctly. The side-scatter factor varies owing to change in the area and/or shape of the field, but the amount of variation is not always linearly proportional to the area of the field. Because the X-ray spectrum depends on the total filtration of the X-ray tube even if the irradiation geometry, X-ray equipment, and tube potential are the same, the side-scatter factor, too, is subject to change. In this paper, we propose a new method of calculation that uses the differential side-scatter factor computed by means of a Monte Carlo simulation, for obtaining the side-scatter factor of diagnostic X-rays. This method, which can calculate the side-scatter factor under any conditions of irradiation, is useful in evaluating the side-scatter factor of diagnostic X-rays.     

低剂量X射线对淋巴细胞及各亚群细胞功能的刺激作用

作者在研究低剂量辐射对全淋巴细胞刺激性效应的同时，用３种单克隆抗体分离出分化抗原簇＋－４，分化抗原簇＋－８和Ｂ细胞亚群，进一步探讨了低剂量辐射对３种亚群细胞的刺激作用。结果表明，Ｐａｎｎｉｎｇ法分离的各亚群细胞的纯度及存活率均在９０％以上；全淋巴细胞在０．１Ｇｙ剂量范围内有刺激作用，尤以０．１Ｇｙ剂量点效应最大；各亚群细胞在０．２Ｇｙ照射内均有刺激性效应的发生．分化抗原簇＋－４和Ｂ细胞在０．１Ｇｙ剂量点效应最强，而分化抗原簇＋－８在０．０５Ｇｙ点效应最强；相同剂量，分化抗原簇＋－４的刺激效应大于分化抗原簇＋－８；０．５Ｇｙ照射则表现出明显的抑制作用．     

Low doses of diagnostic energy X-rays protect against neoplastic transformation in vitro

Purpose : To investigate the effect of low doses of 60 kVp X-rays on in vitro transformation frequency. Materials and methods : HeLa ×skin fibroblast human hybrid cells were used to assay transformation from the non-tumorigenic to the tumorigenic phenotype. Subconfluent cultures of cells were exposed to a range of doses of 60 kVp X-rays and seeded for assay of transformation after 24 h post-irradiation holding. Experiments were repeated at least three times and the data pooled for analysis. Transformation frequencies were compared with those of sham-irradiated controls. Results : At doses < 1 cGy, the observed transformation frequencies were significantly less than those seen in unirradiated cells. Conclusion : Low doses (< 1 cGy) of 60 kVp X-rays protect HeLa ×skin fibroblast human hybrid cells against neoplastic transformation in vitro.     

Low doses of diagnostic energy X-rays protect against neoplastic transformation in vitro

PURPOSE: To investigate the effect of low doses of 60 kVp X-rays on in vitro transformation frequency. MATERIALS AND METHODS: HeLa x skin fibroblast human hybrid cells were used to assay transformation from the non-tumorigenic to the tumorigenic phenotype. Subconfluent cultures of cells were exposed to a range of doses of 60 kVp X-rays and seeded for assay of transformation after 24 h post-irradiation holding. Experiments were repeated at least three times and the data pooled for analysis. Transformation frequencies were compared with those of sham-irradiated controls. RESULTS: At doses < 1 cGy, the observed transformation frequencies were significantly less than those seen in unirradiated cells. CONCLUSION: Low doses (< 1 cGy) of 60 kVp X-rays protect HeLa x skin fibroblast human hybrid cells against neoplastic transformation in vitro.     

Balancing image quality and dose in diagnostic radiology

The formation of images in diagnostic radiology involves a complex interplay of many factors and the ideal balance is to obtain an image, which is adequate for the clinical purpose with the minimum radiation dose. Some factors are classified as physical parameters and can be measured objectively in physical test phantoms, but the diagnostic images must still be interpreted by human observers which does not always mean an ideal observer. This subjective nature of image interpretation makes the objective approach to a full assessment difficult. The ideal method for evaluation of imaging techniques is through clinical trials. Scoring of image quality criteria relating to features observed in a normal clinical radiograph gives a simple method through which image quality can be assessed and related to the radiation dose used. But if optimal performance is to be achieved, it is necessary to understand both the influence of the physical factors in the image formation on dose and image quality and to apply the correct methodology in these analyses of optimisation of the imaging process.     

Equivalent dose and efficient dose in risk assessment of stochastic effects in diagnostic radiology

INTRODUCTION: Purpose. The equivalent dose absorbed during a radiological examination and the resulting effective dose correlate with the probability of late stochastic effects, of which the ICRP 60 has determined the nominal coefficients normalized to 1 Sv. We have normalized the risk coefficients to 1 mSv for better simulation of working conditions. We propose a simple method for estimating the radiological stochastic risk by correctly using both the equivalent dose and the effective dose concepts. MATERIAL AND METHODS: The effective dose depends on the irradiated body volume; thus, we calculated the stochastic risk in three hypothetical radiological examinations. The equivalent dose in the volume irradiated by the main beam was assumed to be 10 mSv and homogeneous; the equivalent dose in adjacent volumes was assumed to decrease by two different dose gradients. In our models, the sum of the equivalent dose absorbed by various tissues multiplied by the different weight-tissue values gives three effective dose values. Finally, the stochastic risk is estimated by multiplying the effective dose values by the nominal risk coefficient determined by ICRP 60. RESULTS: The effective dose is highest when the volume irradiated by the main beam is largest and the dose gradient in adjacent volumes is slowest. With a slow gradient, the effective dose is 10 mSv for total body examinations, 6.25 mSv for abdominopelvic examinations and 1.4 mSv for head and neck examinations. With a fast gradient, the effective dose is 10 mSv, 5.99 mSv and 1.10 mSv, respectively. The lethal tumor probability over the entire life-span is 65/10(6) for head and neck examinations, 300/10(6) for abdominopelvic examinations and 500/10(6) for total body examinations. CONCLUSIONS: The risk of stochastic effects in diagnostic radiology is low, inasmuch as it is projected over the entire life-span of the subject. Nevertheless, it must not be overlooked. Our calculation method aims to explain the correct use of equivalent dose and effective dose concepts, particularly relative to that great majority of radiological examinations which involve limited body volumes. In these cases it is important to estimate correctly the dose gradient from the examined volume towards the adjacent volumes. Close collaboration between physicist and radiologist is therefore essential, as their respective specialist tasks must necessarily be integrated.     

A Study of uncertainty factors in cross calibration of dosimeter for diagnostic X-rays

Although patient exposure has been increasing in recent years, few institutions have dosimeters and are able to ascertain patients' exposure dose. Internationally, however, it is necessary to adopt safety levels for patient exposure doses, and guidance levels have been introduced. Therefore, the need for measurement in areas of x-ray diagnosis has been increasing. As a result, several societies concerned with radiation dose have been endeavoring to establish a calibration system of radiation measurement and a dosimeter calibration system, which are the basics of radiation protection. Ten regional centers for standardization of doses in x-ray diagnosis were established and have begun trials relating to dosimeter cross calibration. Our institution, as one of these centers, has instituted a trial. In this study, the cross-calibration field, the reliability of the cross-calibration skill of our regional center, and the standard uncertainty of cross calibration were investigated. As a consequence of the investigation, it was determined that our cross-calibration field follows the protocol of the Japanese Society of Radiological Technology, the difference between calibration factor/cross calibration factor obtained by JQA and our regional center is within 2.5%, and the expanded uncertainty of our cross calibration is about 7.2% (k=2).     

6MVX射线超高剂量照射人离体血淋巴细胞微核的剂量效应研究

本文用CB微核法研究了超高剂量6MVX射线照射人离体血后微核(MN)的剂量效应关系, 见到剂量高至25Gy仍可见双核cB细胞, 在0～10Gy范围内, MN率与照射剂量呈正相关 关系, 并得到拟合较好的回归方程, 有可能打破近30正来生物剂量估算为5 Gy的上限, 使能直接的估算大于5Gy受照者的生物剂量, 摄高了以MN检测作为生物学剂量计的应用价值。10Gy以上, MN串的上升呈平缓的坪趋势, 在10～25Gy范围内虽不能精确的估算剂量, 但片中双核CB细胞的多少, 对判断剂量有—定参考价值。     

Effective dose to children and adolescents from radiopharmaceuticals.

Published values of tissue weighting factors for adolescents and children derived from the life-span study of the atomic bomb survivors have been used to calculate the effective dose to patients aged 1, 5, 10 and 15 years undergoing a common paediatric procedure requiring one of the following radiopharmaceuticals: 99Tcm-mercaptoacetyltriglycine (MAG3), 99Tcm-diethylenetriaminepentaacetic acid (DTPA), 99Tcm-dimercaptosuccinic acid (DMSA), 99Tcm-pertechnetate, 99Tcm-iminodiacetic acid (IDA) derivatives, 99Tcm-hexamethylpropyleneamineoxine (HMPAO), 99Tcm-labelled leukocytes, 99Tcm-labelled erythrocytes, 99Tcm-phosphates, 99Tcm-methyloxyisobutylisonitrile (MIBI), 201Tl-chloride, sodium 123I-iodide, 123I-metaiodobenzylguanidine (MIBG) and 67Ga-citrate. Administered activities for each age group were based on ARSAC maximum usual values for adult patients and scaling factors listed by the European Association of Nuclear Medicine for different body weights. These effective doses were compared to values derived from ICRP whole-population tissue weighting factors and found to differ by -33% to +71% of these values, and by less than +/- 20% for two-thirds of the procedures. Because these differences were considerably less than the uncertainties in the estimates of organ absorbed dose, we conclude that these published age-specific tissue weighting factors should not be used for the estimation of effective dose to children and adolescents following the administration of radiopharmaceuticals, and that whole-population factors should continue to be used for these estimations.