Radiation dose to family members of hyperthyroidism and thyroid cancer patients treated with 131I

The thermoluminescence dosemeter (TLD) was used for measuring radiation dose to family members of thyrotoxicosis and thyroid cancer patients treated with (131)I using CaSO(4):Dy discs. There were 45 family members of thyrotoxicosis patients, who were divided into two groups with 22 in the first and 23 in the second group. Radiation safety instructions were the same for both the groups except in the second group where the patients were advised to use a separate bed at home for the first 3 d of dose administration. An activity ranging from 185 to 500 MBq was administered to these patients. The whole-body dose to family members ranged from 0.4 to 2.4 mSv (mean 1.1 mSv) in the first group and 0-1.9 mSv (mean 0.6 mSv) in the second group. A total of 297 family members of thyroid cancer patients were studied for whole-body dose estimation. An activity ranging from 0.925 to 7.4 GBq was administered to the thyroid cancer patients. The family members were divided into three groups depending upon the mode of transport and facilities available at home to avoid close proximity with the patient. Group A with 25 family members received a dose ranging from 0 to 0.9 mSv (mean 0.4 mSv), group B with 96 family members received a dose ranging from 0 to 8.5 mSv (mean 0.8 mSv) and group C with 176 family members received a dose ranging from 0 to 5.0 mSv (mean 0.8 mSv). The thyroid monitoring was also done in 103 family members who attended the patients in isolation wards for >2 d. Thyroid dose in them ranged from 0 to 2.5 mGy (mean 0.1 mGy).     

131I exhalation by patients undergoing therapy of thyroid diseases

In the departments of nuclear medicine, patients are treated with relatively large activities of (131)I for therapeutic purposes. The applied activities are in the range of 200-10 000 MBq. Consequently, individuals situated in the dwellings of the patients dismissed from the hospital are subjected to an external as well as an internal radioiodine exposition. Internal exposition is due to the inhalation of (131)I exhaled by the patients. In this article, the measurements of radioactivity exhaled by patients with various thyroid diseases, treated with (131)I in the department of Nuclear Medicine of the Radiological Centre in Goettingen and in the Hospital of Nuclear Medicine in Wuerzburg are presented. The measurements of activities exhaled by patients were repeated daily, up to 25 d after the treatment. In addition, the residual activities were monitored by measuring the external dose rates, and by measuring the (131)I activity in the urine of these patients. In some cases, the exhaled radioiodine was separated into three fractions: the elemental, the organically bound and the aerosol-bound iodine fraction. On the basis of the proposed measurements, the doses received by the family members of a discharged patient treated with (131)I were estimated by a model calculation.     

Study of the correlation between administered activity and radiation committed dose to the thyroid in 131I therapy of Graves' disease

Substantial reduction in the thyroid volume (up to 70-80%) after 131I therapy of Graves' disease has been demonstrated and reported in the literature. Recently a mathematical model of thyroid mass reduction during the first month after therapy has been developed and a new algorithm for the radiation committed dose calculation has been proposed. Reduction of the thyroid mass and the radiation committed dose to the gland depend on a parameter k, defined for each subject. The calculation of k allows the prediction of the activity to administer, depending on the radiation committed dose chosen by the physician. In this paper a method for calculating k is proposed. The calculated values of k are compared to values derived from measurements of the changes in thyroid mass in twenty-six patients treated by 131I for Graves' disease. The radiation committed dose to the thyroid can be predicted within 21%, and the radioiodine activity to administer to the patient can be predicted within 22% using the calculated values of k. The thyroid volume reduction during the first month after therapy administration can be also predicted with good accuracy using the calculated values of k. The radiation committed dose and the radioiodine activity to administer were calculated using a new, very simple algorithm. A comparison between the values calculated by this new algorithm and the old, classical Marinelli-Quimby algorithm shows that the new method is more accurate.     

Release criteria from hospitals of 131I thyrotoxicosis therapy patients in developing countries--case study

The current release limit, recommended by the International Atomic Energy Agency (IAEA)(1), from hospitals of patients undergoing 131I thyrotoxicosis therapy is approximately 1100 MBq (approximately 30 mCi). Owing to the difference in socio-economic conditions, literacy rate, family system, etc., this release limit may not be applicable in most of the developing countries like Pakistan. Therefore, the prime objective of this case study was to re-evaluate the release criteria for 131I thyrotoxicosis therapy patients by taking into account their lifestyle, economic conditions and other facilities such as availability of private/public transport, etc. In this context, systematic studies were carried out and 50 patients (i.e. 35 outpatients and 15 inpatients) at the Nuclear Medicine Oncology and Radiotherapy Institute (NORI), Islamabad, were studied. Exposure rate at the surface of the body and at a distance of 1 m from the standing patient was measured. Results obtained from this study showed that the dose equivalent delivered by these patients to their family members (particularly children) and general public was higher than annual dose limits recommended by the International Commission for Radiation Protection in their report ICRP Publication 60(2). In the light of this study, it is recommended that the release activity limit of approximately 370 MBq (or dose rate level of approximately 10 microSv h-1 at 1 m from the patient) be adopted instead of approximately 1100 MBq in developing countries like Pakistan.     

Uncertainty of the thyroid dose conversion factor for inhalation intakes of 131I and its parametric uncertainty

Inhalation exposures of 131I may occur in the physical form of a gas as well as a particulate. The physical characteristics pertaining to these different types of releases influence the intake and subsequent dose to an exposed individual. The thyroid dose received is influenced by the route through which 131I enters the body and its subsequent clearance, absorption and movement throughout the body. The radioactive iodine taken up in the gas-exchange tissues is cleared to other tissues or absorbed into the bloodstream of the individual and transferred to other organs. Iodine in the circulatory system is then taken up by the thyroid gland with resulting dose to that tissue. The magnitude of and uncertainty in the thyroid dose is important to the assessment of individuals exposed to airborne releases of radioiodine. Age- and gender-specific modelling parameters have resulted in significant differences between gas uptake, particulate deposition and inhalation dose conversion factors for each age and gender group. Inhalation dose conversion factors and their inherent uncertainty are markedly affected by the type of iodine intake. These differences are expected due to the modelling of particulate deposition versus uptake of gas in the respiratory tract. Inhalation dose estimates via iodine gases are very similar and separate classifications may not be necessarily based on this assessment.     

Implementation of a card with instructions for patients treated for thyroid carcinoma with 131I

Patients discharged after their treatment with (131)I can become invisible sources of radiation for some members of the public. Even people who know that those patients have been treated with (131)I can easily forget the radiological risks that they represent. For this reason, it is essential to ensure that patients follow some instructions for a number of days until their remaining activity is low enough to irradiate members of the public under the recommended effective dose limits. Results in this study show that the number of days on which patients have to follow the mentioned instructions shows certain heterogeneity. Therefore, an individualised card with instructions given to patients after being discharged will tell them when they can restart their normal life, guaranteeing that members of the public do not receive an effective dose over the recommended limits.     

Stress intensity factors for tunnelling corner cracks under mode I loading

Stress intensity factors (SIFs) presented in the literature for corner cracks are limited to ideal quarter-circular and quarter-elliptical crack shapes. This paper presents SIF solutions for corner cracks that exhibit tunnelling, extending the range of corner crack shapes illustrated in the literature. Solutions were developed in a parametric form, obtained by empirically fitting polynomials to numerical values of SIF obtained from the FEM. A parameter was defined to quantify the extent of tunnelling. It was observed that crack shape has a significant effect on the SIF, so the consideration of equivalent quarter-circular cracks can produce inaccurate results when significant tunnelling occurs. SIF solutions for quarter-circular cracks are also presented and compared with those quoted in the literature.     

Inhalation dose due to presence of 131I in air above septic tank system of an endocrinology hospital

We present here measurements of the 131I concentration for both: gaseous and aerosol fraction of 131I in the air above the septic tank containing wastes from medical application of this isotope. Aerosols were collected using air filters, whereas gaseous forms of iodine were trapped in KI impregnated charcoal double layer cartridge. Besides an active method (pumping of the air through system of filters) an attempt for using a passive method (charcoal traps) for monitoring of radio-iodine is described. For better characterisation of a site the external kerma was determined by means of G-M and TLD techniques as well as the activity kept in the septic tank was measured by gamma spectrometry. Results show that the activity of the aerosol fraction can be neglected compared to that of the gaseous fraction. He measured activity of air is low, on the level of 1 Bq m(-3), even during simulated failure of the ventilation system. Estimated inhalation dose for the serviceman of septic tanks is low ( approximately 10%) compared with external dose obtained by such person due to gamma radiation from the tank (on the level approximately 500 nSv h(-1)). Therefore, the concept of passive monitoring of the iodine in air was abandoned. Also estimated is the efficiency of 131I reduction by a charcoal filter of the ventilation system and 131I input to the environment by the ventilation chimney.     

Criteria for patient release according to external dose rate and residual activity in patients treated with 131I-sodium iodide in Iran

External dose rate (ED) and residual activity (RA) of patients treated with (131)I sodium iodide are two main factors, to consider before release of patients. In this study, six nuclear medicine centres out of total seven centres in Iran were selected and measurements have been done on 330 patients. ED of patients was measured by physicists of the centres for 6 months (May-November 2009) at a 1 m distance from the thyroid of each patient on the first, second and third days after administration by a calibrated survey meter. The maximum and minimum values of ED were 21 (SD = 18) and 11 (SD = 4) μSv h(-1), respectively. Furthermore, the maximum and minimum values of RA during release of patient were 720 and 250 MBq, respectively. According to the study, we recommend a release activity limit of 500 MBq (14 mCi) or a dose rate level of 20 μSv h(-1) at 1 m from the patient to be set instead of a release activity limit of 1100 MBq (30 mCi) as it is now for the country.     

3D calculation of absorbed dose for 131I-targeted radiotherapy: a Monte Carlo study

Various methods, such as those developed by the Medical Internal Radiation Dosimetry (MIRD) Committee of the Society of Nuclear Medicine or employing dose point kernels, have been applied to the radiation dosimetry of (131)I radionuclide therapy. However, studies have not shown a strong relationship between tumour absorbed dose and its overall therapeutic response, probably due in part to inaccuracies in activity and dose estimation. In the current study, the GATE Monte Carlo computer code was used to facilitate voxel-level radiation dosimetry for organ activities measured in an (131)I-treated thyroid cancer patient. This approach allows incorporation of the size, shape and composition of organs (in the current study, in the Zubal anthropomorphic phantom) and intra-organ and intra-tumour inhomogeneities in the activity distributions. The total activities of the tumours and their heterogeneous distributions were measured from the SPECT images to calculate the dose maps. For investigating the effect of activity distribution on dose distribution, a hypothetical homogeneous distribution of the same total activity was considered in the tumours. It was observed that the tumour mean absorbed dose rates per unit cumulated activity were 0.65E-5 and 0.61E-5 mGY MBq(-1) s(-1) for the uniform and non-uniform distributions in the tumour, respectively, which do not differ considerably. However, the dose-volume histograms (DVH) show that the tumour non-uniform activity distribution decreases the absorbed dose to portions of the tumour volume. In such a case, it can be misleading to quote the mean or maximum absorbed dose, because overall response is likely limited by the tumour volume that receives low (i.e. non-cytocidal) doses. Three-dimensional radiation dosimetry, and calculation of tumour DVHs, may lead to the derivation of clinically reliable dose-response relationships and therefore may ultimately improve treatment planning as well as response assessment for radionuclide therapy.     

Mode I stress intensity factors and weight functions for short plates under different boundary conditions

Stress intensity factors and weight functions are available in literature predominantly for cracked components under stress boundary conditions. In order to provide weight function solutions including displacement boundary conditions, rectangular plates with different length-to-width ratios are studied using the boundary collocation method. The results are reported in the form of figures and tables. The influence of Poisson’s ratio is discussed in detail. It can be concluded from the numerical data and theoretical considerations that the mode I stress intensity factors and weight functions are independent of Poisson’s ratio ν for mixed boundary conditions at the plate ends, but depend on ν in case of pure displacement conditions.     

Simplified model for the fatigue growth analysis of surface cracks in round bars under mode I

The fatigue growth of an edge flaw in a round bar under cyclic tension or bending loading is examined, using a two-parameter numerical model. First, it is shown that the crack front evolution is defined by a very small number of parameters, which varies during crack growth. Approximated solutions for both the crack propagation path and the stress intensity factor are derived, and the fatigue predictions using this simple analytical method are finally compared with the numerical results.     

Senescence of spatial chromatic contrast sensitivity. I. Detection under conditions controlling for optical factors

Chromatic contrast thresholds for spatially varying patterns of various spatial frequencies (0.5, 1, 2, and 4 cycles per degree) were measured for ten older (65-77 yr of age) and ten younger (18-30 yr of age) observers. The stimuli were Gabor patches modulated along S-varying or (L - M)-varying chromatic axes. Thresholds were determined for two sets of stimuli. For one set of stimuli, the mean chromaticity and luminance were equated at the cornea for all observers. The second set of stimuli was corrected for ocular media density differences to equate stimulation of each of the three cone types at the retina for each individual. Chromatic contrast thresholds were higher for older observers for all stimuli tested. The magnitude of this difference showed little dependence on spatial frequency. When stimuli were equated at the cornea, this difference was greater for S-varying stimuli. When stimuli were equated at the retina, the age-related difference in thresholds for S-varying stimuli was reduced. Both optical and neural factors contribute to these age-related losses in spatial chromatic contrast sensitivity.     

Hydrodynamic effects responsible for the modification of polysaccharides in an aqueous solution under laser irradiation

An attempt to determine factors responsible for the degradation of polysaccharide molecules in aqueous solutions under the action of laser radiation was undertaken. For this purpose, free-falling drops of water containing polysaccharides were irradiated by a laser beam and the corresponding hydrodynamical model was constructed. Laser irradiation of a drop of an aqueous solution of polysaccharides leads to the formation of oligosaccharides which can be applied in medicine.     

立体定向放射治疗计划输出剂量的验证

本文简单介绍对加速器的立体定向治疗计划的输出剂量进行的验证测量，其测量结果和治疗计划预制输出剂量在-1．1％内吻合。并利用胶片法测量了立体定向治疗计划的输出剂量的分布，其测量结果与治疗计划输出剂量分布的80％等剂量曲线面积重合率为94％，得到较满意的结果。     

立体定向放射治疗计划输出剂量的验证

本文简单介绍对加速器的立体定向治疗计划的输出剂量进行的验证测量,其测量结果和治疗计划预制输出剂量在-1 1%内吻合。并利用胶片法测量了立体定向治疗计划的输出剂量的分布,其测量结果与治疗计划输出剂量分布的80%等剂量曲线面积重合率为94%,得到较满意的结果。     

A re-evaluation of the occupancy factors for effective dose estimate in tropical environment

In the estimation of the effective dose to the public, outdoor and indoor occupancy factors have been an important parameter. These factors vary, depending on the prevailing environmental condition in a particular location. The factors have been estimated for the rural and urban areas in Nigeria. An outdoor factor of 0.3 and 0.22 have been estimated for rural and urban dwellers, respectively. The rural outdoor factor is 50% above the value recommended as the world average by the UNSCEAR. The urban outdoor factor is 10% higher than this value. The total outdoor gamma dose rate in the air due to (40)K, (238)U and (232)Th in the soil for some rural population in the southern part of Nigeria is 29.50 +/- 3.80 nGy h(-1) and the average outdoor effective dose has been estimated to be 54.28 +/- 6.95 microSv y(-1) using the present occupancy factor.     

Quantitative risk analysis for toxic chemicals in the environment

An overview and basic framework is presented for quantification of human health risks associated with toxic chemicals in the environment. The presentation is designed for program managers who require an introduction to the principles of risk analysis and an understanding of the current state-of-the-art. The basic terminology is explained, the methodological components are reviewed, and a series of procedures is discussed for estimating ambient concentrations, effect potency, and human exposure and risk levels for a chemical substance. Practical considerations are discussed, including the uncertainties introduced by data gaps and modelling assumptions. Finally, a simple numerical illustration of the calculation procedures is presented.