Calculation of fluence and absorbed dose in head tissues due to different photon energies

Calculations of fluence and absorbed dose in head tissues due to different photon energies were carried out using the MCNPX code, to simulate two models of a patient's head: one spherical and another more realistic ellipsoidal.Both head models had concentric shells to describe the scalp skin, the cranium and the brain. The tumor was located at the center of the head and it was a 1 cm-radius sphere. The MCNPX code was run for different energies.Results showed that the fluence decreases as the photons pass through the different head tissues.It can be observed that, although the fluence into the tumor is different for both head models, absorbed dose is the same.     

Calculation algorithm of three-dimensional absorbed dose distribution due to in vivo administration of nuclides for radiotherapy]

In the in vivo administration of radionuclides for radiotherapy including radioimmunotherapy, an algorithm is proposed for the purpose of calculating three-dimensional absorbed dose distributions of tumors and adjacent tissues, and neighboring organs. The absorbed dose distribution due to the algorithm is given by convolution of the three-dimensional dose matrix for a unit cubic voxel containing unit cumulated activity, with the three-dimensional matrix of the cumulated activity distribution given by the same voxel size above. The dose calculation algorithm does not depend upon the source size, the source shape, and the nonuniform and irregular activity distribution. In addition, it can exceedingly decrease computation time compared to other calculation algorithms. Computer simulations were performed using the MIRD thyroid phantom for 32P, 90Y, 131I, 186Re, and 188Re that appear promising for radioimmunotherapy, and their results verified the validity of the proposed calculation algorithm and high accuracy of the calculations.     

Effective dose from radiopharmaceuticals.

The effective dose, as defined by the International Commission on Radiological Protection (ICRP 1991), provides a possibility of expressing the radiation risk to patients undergoing different radiodiagnostic procedures by means of a single figure. This has been obtained by introducing organ or tissue weighting factors reflecting the radiation sensitivity of the organs. Such weighting factors were first published by the ICRP in publication 26 (1977), and have now been revised in publication 60 (1991). The effective dose for almost all radiopharmaceuticals in clinical use has been recalculated using the new weighting factors from ICRP 60 (1991) and compared with results from former calculations. A slight decrease in the numerical value for the effective dose has been observed, on average 11%. However, this does not correspond to a decrease in the estimated risk from the irradiation, since this has been re-evaluated and found to be higher than earlier believed (NAS 1990; ICRP 1991).     

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.     

Uncertainties in internal dose calculations for radiopharmaceuticals.

This paper presents a systematic analysis of the inherent uncertainty in internal dose calculations for radiopharmaceuticals. A generic equation for internal dose is presented, and the uncertainty in each of the individual terms is analyzed, with the relative uncertainty of all terms compared. The combined uncertainties in most radiopharmaceutical dose estimates will be typically at least a factor of 2 and may be considerably greater. In therapy applications, if patient-individualized absorbed doses are calculated, with attention being paid to accurate data gathering and analysis and measurement of individual organ volumes, many of the model-based uncertainties can be removed, and the total uncertainty in an individual dose estimate can be reduced to a value of perhaps +/-10%-20%. Radiation dose estimates for different diagnostic radiopharmaceuticals should be appreciated and considered, but small differences in dose estimates between radiopharmaceuticals should not be given too much importance when one is choosing radiopharmaceuticals for general clinical use. Diagnostic accuracy, ease of use, image quality, patient comfort, and other similar factors should predominate in the evaluation, with radiation dose being another issue considered while balancing risks and benefits appropriately.     

贴壁细胞β射线内照射吸收剂量的计算

目的：寻求贴壁细胞β射线内照射吸收剂量的计算公式。方法：根据辐射吸收剂量定义和MIRD方案进行推导。从悬浮细胞培养模式入手,考虑到贴壁细胞培养的特殊性,以及其受照射的方向,依据累积放射性活度、β射线能量、培养液质量计算辐吸收剂量。结果：得到悬浮细胞、贴壁细胞β射线内照射吸收剂量的计算公式。并进行计算验证。结论：该公式使用简便,可靠性强,准确性好,便于实际应用。     

Estimating the absorbed dose to critical organs during dual X-ray absorptiometry.

OBJECTIVE: The purpose of this study is to estimate a patient's organ dose (effective dose) during performance of dual X-ray absorptiometry by using the correlations derived from the surface dose and the depth doses in an anthropomorphic phantom. MATERIALS AND METHODS: An anthropomorphic phantom was designed and TLDs (Thermoluminescent Dosimeters) were placed at the surface and these were also inserted at different depths of the thyroid and uterus of the anthropomorphic phantom. The absorbed doses were measured on the phantom for the spine and femur scan modes. The correlation coefficients and regression functions between the absorbed surface dose and the depth dose were determined. The derived correlation was then applied for 40 women patients to estimate the depth doses to the thyroid and uterus. RESULTS: There was a correlation between the surface dose and depth dose of the thyroid and uterus in both scan modes. For the women's dosimetry, the average surface doses of the thyroid and uterus were 1.88 microGy and 1.81 microGy, respectively. Also, the scan center dose in the women was 5.70 microGy. There was correlation between the thyroid and uterus surface doses, and the scan center dose. CONCLUSION: We concluded that the effective dose to the patient's critical organs during dual X-ray absorptiometry can be estimated by the correlation derived from phantom dosimetry.     

An absorbed dose conversion factor due to the x-ray spectrum compare with the method by the half-value layer

When the absorbed dose conversion factor of the x-rays is looked for, generally it is being done how to measure the effective energy (keV) from the half-value layer. But, spectrum measurement is necessary to evaluate quality of x-ray precisely. So, 2.94% of the maximum differences were in the water, soft tissue, and 20.93% of the maximum differences were in search of absorbed dose conversion factor due to the half-value layer and the spectrum as a compared result by cortical bone. And, when a x-ray tube voltage rose, this difference showed a tendency of spreading out. A cause was because the rates of the photon of the higher energy than the energy measured with effective energy increased by a x-ray tube voltage's rising. The ratio of the mass energy absorption coefficient which faces air like cortical bone should be careful because an error by the absorbed dose conversion factor grows big when a absorbed dose conversion factor is measured by the big absorption medium, though it is as the difference in absorbed dose conversion factor is compared with an error by the dosimeter and there is no problem in the water, soft tissue.     

Dosimetry of swallowed non absorbed99mTc radiopharmaceuticals in pediatric patients

A calculation is presented which derives the absorbed dose experienced by pediatric patients of different ages who swallow a non absorbable^99mTc compound. All previous models assume sudden movement of radionuclide from one compartment of the gastrointestinal tract to another. The present model is novel in considering continuous distal motion through the gut and so more closely approximates the physiologic situation. Published S values are used to derive absorbed doses. The resulting calculated absorbed doses are comparable to, or lower than, those previously published and these differences are most marked in the large gut, which remains the critical organ.     

Dosimetry of swallowed non absorbed 99mTc radiopharmaceuticals in pediatric patients

A calculation is presented which derives the absorbed dose experienced by pediatric patients of different ages who swallow a non absorbable 99mTc compound. All previous models assume sudden movement of radionuclide from one compartment of the gastrointestinal tract to another. The present model is novel in considering continuous distal motion through the gut and so more closely approximates the physiologic situation. Published S values are used to derive absorbed doses. The resulting calculated absorbed doses are comparable to, or lower than, those previously published and these differences are most marked in the large gut, which remains the critical organ.     

Factors influencing the absorbed dose in intraoral radiography

OBJECTIVES: The aim of the present study was to find out whether it was more effective to achieve a dose reduction in intraoral radiography with an increase in the tube potential setting (and a decrease of milliampere seconds) by an additional attenuation of the X-ray beam behind the film plane or by the use of digital radiography. A second aim was to find out if there were differences between the integral doses determined by two different detectors and two different phantoms. METHODS: The X-ray attenuation in this in vitro study was carried out using additional lead foils from the dental film packet fixed behind the film plane and with a metal film holder. The dose measurements were performed with two semiconductor detectors (Quart, Diados). Patient simulation was achieved by the Alderson phantom or by the use of a filter (6Al+0.8Cu). The absorbed doses were calculated by integrating an exponential function between the entrance dose and the body exit dose. In addition, organ doses were measured and the effective dose was determined according to the Implementation of the 1990 Recommendations of the ICRP (ICRP-60). RESULTS: The increase in tube potential levels did not provide a substantial reduction of the absorbed dose (90 kVp instead of 60 kVp: reduction to 92.4%), only a reduction of the entrance dose (by 30% to 35% at 90 kVp compared with 60 kVp). The use of three lead foils behind the film plane instead of one resulted in a 14.0% reduction of the absorbed dose (60 kVp); the use of a metal film holder resulted in a 27.8% reduction (60 kVp). When tube potential settings were increased, the dose reduction decreased. The absorbed dose was reduced to 52% when a storage phosphor plate was used instead of a film (60 kVp). It was possible to determine the amount of dose reduction with both the calculated absorbed dose and the effective doses. The integral doses obtained from the Alderson phantom showed values 5% higher than those obtained by the filter (r(2)=96.7%). For the comparison of the integral doses, the measurements performed with Quart had values higher by a factor of 1.139 than those performed with Diados. CONCLUSIONS: Instead of increasing the tube voltage or using additional lead foils or metal film holders, a substantial dose reduction is provided by digital radiography or more sensitive films while a low tube potential level is maintained and the milliampere seconds setting is reduced.     

An integrated approach to biodistribution radiation absorbed dose estimates

An integrated approach to existing methods of extracting biodistribution data, pharmacokinetics and radiation absorbed dose estimates from serial scintigraphic images is described. This approach employs a single computer-generated user interface to reformat planar scans into a standard file type, align conjugate (anterior and posterior) images, draw regions of interest (ROIs) over selected organs and lesions and generate count data for anterior and posterior views and calculated geometric means. Using standard correction methods, the fraction injected activity is obtained for all ROIs and total body. This methodology has been applied to the analysis of indium-III-labelled breast-cancer-directed antibodies and technetium-90m-labelled CEA-specific antibody fragments in non-small-cell lung cancer. It is anticipated that this approach will be useful for evaluating the dosimetry of other radiolabelled monoclonal antibodies, as well as other radiopharmaceuticals.