Peculiarities of Using Lymphocyte Test to Predict the Severity of Acute Radiation Injury

One of the methods of biological dosimetry is the use of information on the concentration of lymphocytes in the peripheral blood of victims in the first days after irradiation. The aim of the study was to validate the lymphocyte test method for predicting the severity of acute radiation injury, taking into account the dose rate factor. Materials and research methods. The method of investigation was a correlational analysis of clinical, dosimetric and laboratory data of the victims of the accident at the Chernobyl nuclear power plant in 1986 (n=65) and in radiation accidents with gamma-neutron irradiation (n=19). The data were taken from the database of acute radiation injuries in humans of A.I. Burnazyan Federal Medical Biophysical Center of the Federal Medical and Biological Agency of Russia. Results of the study and their analysis. The results of correlation analysis indicated that average lymphocyte concentration in the range of 0.4-0.8×109/l on day 3-6 post-irradiation with dose rates greater than 2 Gy/h resulted in an average dose estimate which was 40.0% higher than that for dose rates of less than 2 Gy/h. Absolute error of dose estimation is (±1.0-1.5) Gy. For lymphocyte concentrations higher than 0.8×109/l the prognosis is uncertain: the range of dose assessment variability is 1-4 Gy. At a lymphocyte concentration of less than 0.4×109/l the average dose estimate is more than 4.0 Gy, corresponding to a severe or extremely severe degree of acute radiation disease. The predicted degree of severity of radiation injuries in the presence of the neutron component of radiation is lower in comparison with the predictions based on the data on the victims of the Chernobyl accident. It is concluded that the identified dependencies can be used for medical triage of the victims at advanced stages of medical evacuation. For the purpose of correct routing of medical evacuation to specialized centers, it is advisable to allocate 4 treatment-evacuation groups.

SIZE-SPECIFIC DOSE ESTIMATES FOR PEDIATRIC NON-CONTRAST HEAD CT SCANS: A RETROSPECTIVE PATIENT STUDY IN TUNJA, COLOMBIA

This investigation is aimed to study the feasibility of size-specific dose estimate (SSDE) to patient dosimetry in pediatric head CT scans and to establish typical values in a hospital in Tunja, Colombia. The volumetric computed tomography index (CTDIvol) and the dose-length product of 468 pediatric patients from newborn to 15-year-olds, who underwent non-contrast head CT scans, were collected retrospectively. For 186 cases only, SSDE was estimated using patient attenuated-based size metrics and CTDIvol,16-to-SSDE conversion factors reported in AAPM report 293. Results showed that SSDE is an accurate metric that can be used to establish typical dose values from pediatric head CT scans. Median SSDE values of 33.5, 31.6, 36.2 and 57.9 mGy were established as typical dose values for the 0–<3 months, 3 months–<1 y, 1–<6 y and ≥6 y, respectively, to further assist the optimization process at the hospital. Further studies with more robust data of patients and hospitals should be conducted to establish local and national dose reference levels from pediatric CT scans in Colombia.

A simple manual method to estimate water-equivalent diameter for calculating size-specific dose estimate in chest computed tomography

Objectives: The American Association of Physicists in Medicine (AAPM) Task Groups (TG) 204 and 220 introduced a method to estimate patient dose by introducing the Size-Specific Dose Estimate (SSDE). They provided patient size-specific conversion factors that could be applied to volumetric CT Dose Index CTDIvol to estimate patient dose in terms of SSDE based on either effective diameter (Deff) or water equivalent diameter (Dw). Our study presented an alternative method to manually estimate SSDE for the everyday clinical routine chest CT that can be readily used and does not require sophisticated computer programming. Methods: For 16 adult patients undergoing chest CT, the method employed an average relative electron density (ρelung = 0.3) for the lung tissue and a ρetissue of 1.0 for the other tissues to scale the lateral thickness and compute the effective lateral thickness on the patient’s axial image. The proposed method estimated a “corrected” Deff (Deffcorr) to replace Dw and compared results with TG220 and a second method proposed by Huda et al, for the same set of CT studies. Results: The results showed comparable behavior for all methods. There is overall agreement especially between this study and TG220. Largest differences were +13.3% and+15.9% from TG220 and Huda values, respectively. Patient size correlation showed strong correlation with the TG220 and Huda et al methods. Conclusions: A simple, quick manual method to estimate CT patient radiation dose in terms of SSDE was proposed as an alternative where sophisticated computer programming is not available. It can be readily used during any clinical chest CT scanning. Advances in knowledge: The paper is novel as it presents simple, quick manual method to estimate CT patient radiation dose in chest imaging. The process can be used as alternative in cases no sophisticated computer programming is available.

DEVELOPMENT OF A SPECIALISED TAPE MEASURE TO ESTIMATE THE SIZE-SPECIFIC DOSE ESTIMATE

The risk in computed tomography (CT) examinations is radiation exposure. We aimed to develop a specialised tape measure for determining the size-specific dose estimate (SSDE) for patients undergoing CT scans. The scanning parameters used were those of the abdominal protocol in our institute. With this method, the SSDE220 and standard deviations obtained from CT images for the liver, pelvic and lung areas, corresponded closely to the SSDEtape and standard deviations obtained using the tape measure. We thus devised a new idea that allows the estimation of the SSDE220 using a specialised tape measure before the CT examination, allowing for an informed explanation of the radiation dose to the patient. Although the tape measure developed in this study is specific to one particular CT instrument, the method could be adapted to a wide range of radiography applications.