During proton beam radiotherapy, discrete secondary prompt gamma rays are induced by inelastic nuclear reactions between protons and nuclei in the human body. In recent years, the Geant4 Monte Carlo toolkit has played an important role in the development of a device for real time dose range verification purposes using prompt gamma radiation. Unfortunately the default physics models in Geant4 do not reliably replicate the measured prompt gamma emission. Determining a suitable physics model for low energy proton inelastic interactions will boost the accuracy of prompt gamma simulations. Among the built-in physics models, we found that the precompound model with a modified initial exciton state of 2 (1 particle, 1 hole) produced more accurate discrete gamma lines from the most important elements found within the body such as 16O, 12C and 14N when comparing them with the available gamma production cross section data. Using the modified physics model, we investigated the prompt gamma spectra produced in a water phantom by a 200 MeV pencil beam of protons. The spectra were attained using a LaBr3 detector with a time-of-flight (TOF) window and BGO active shield to reduce the secondary neutron and gamma background. The simulations show that a 2 ns TOF window could reduce 99% of the secondary neutron flux hitting the detector. The results show that using both timing and active shielding can remove up to 85% of the background radiation which includes a 33% reduction by BGO subtraction.
This study aims to review the existing literature on diagnostic reference levels (DRLs) in paediatric computed tomography (CT) procedures and the methodologies for establishing them. A comprehensive literature search was done in the popular databases such as PubMed and Google Scholar under the key words ‘p(a)ediatric DRL’, ‘dose reference level’, ‘diagnostic reference level’ and ‘DRL’. Twenty-three articles originating from 15 countries were included. Differences were found in the methods used to establish paediatric CT DRLs across the world, including test subjects, reference phantom size, anatomical regions, modes of data collection and stratification techniques. The majority of the studies were based on retrospective patient surveys. The head, chest and abdomen were the common regions. The volume computed tomography dose index (CTDIvol) and dose–length product (DLP) were the dosimetric quantities chosen in the majority of publications. However, the size-specific dose estimate was a growing trend in the DRL concept of CT. A 16 cm diameter phantom was used by most of the publications when defining DRLs for head, chest and abdomen. The majority of the DRLs were given based on patient age, and the common age categories for head, chest and abdomen regions were 0–1, 1–5, 5–10 and 10–15 years. The DRL ranges for the head region were 18–68 mGy (CTDIvol) and 260–1608 mGy cm (DLP). For chest and abdomen regions the variations were 1.0–15.6 mGy, 10–496 mGy cm and 1.8–23 mGy, 65–807 mGy cm, respectively. All these DRLs were established for children aged 0–18 years. The wide range of DRL distributions in chest and abdomen regions can be attributed to the use of two different reference phantom sizes (16 and 32 cm), failure to follow a common methodology and inadequate dose optimisation actions. Therefore, an internationally accepted protocol should be followed when establishing DRLs. Moreover, these DRL variations suggest the importance of establish a national DRL for each country considering advanced techniques and dose reduction methodologies.
The actual dose received during a computed tomography (CT) examination depends on both the patient size and the radiation output of the scanner. To represent the actual patient morphometry, a new radiation dose metric named size-specific dose estimates (SSDEs) was developed by the American Association of Physicists in Medicine in 2011. The purpose of this article is to review the SSDE concept and the factors influencing it. Moreover, the appropriate methodology of SSDE determination and the application of SSDE as a diagnostic reference-level quantity is critically analyzed based on the data available in the literature. It is expected that this review could potentially increase awareness among CT users of the effective utilization of SSDE as a tool to aid in the optimization of radiation dose in CT.
Determination of age is really important and sometimes it is a difficult task in medicolegal practices. Aim of this study was to confirm whether the status of the fusion at xiphisternal joint can be used to estimate the age. Total of 275, who underwent computed tomography (CT) thoracic examination, were selected as the study sample. RadiAnt Digital Imaging and Communications in Medicine (DICOM) viewer was used to observe the fusion state. There was a negative correlation between fusion category and age in males (r = -0.325, p < 0.001), no significant correlation in females (r = 0.094, p = 0.346) and, a negatively significant correlation (r = -0.165, p = 0.006) in both sexes. There was a statistically significant difference in age between different fusion categories, χ2 (2) = 63.61, p < 0.001 in males, χ2 (2) = 31.98, p < 0.001 in females and, χ2 = 97.76, p < 0.001 in both sexes. There was a strong negative correlation between non-fusion age and distance of joint space in males (r = -0.479, p = 0.006), in females (r = -0.963, p < 0.001) and, in both sexes (r = -0.758, p < 0.001).
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