Iranian Journal of Medical Physics
Volume:16 Issue: 4, Jul-Agust 2019

Ionizing radiation is widely used in industry and medicine; however, it causes a significant health hazard by making microscopic damage to living tissue. Various biological parameters, including cell survival fraction and relative biological effectiveness, are taken into account to assess the severity and extent of biological damages. Microdosimetry suffers from various shortcomings and limitations, but the development of some powerful simulation software has paved the way to resolve these problems in recent years. In this study, the authors were looked for two keywords (Geant4 and radiobiology) in the title, abstracts, and keywords of Scopus and PubMed database articles. More than 100 articles were found. The researchers extracted the articles that were devoted to the construction of different geometries for DNA, nucleus, and cells as simulate the parameters, such as relative biological effectiveness, SF, linear energy transfer, and single-strand breaks/double-strand breaks in the present study. Geant4 is one of the software commonly used to simulate biological factors. It has many properties, such as the ability to follow up physical processes in very low energy, open source code, and flexibility in complex geometries. In this paper, we reviewed some of the radiobiological parameters simulated with Geant4.

The effects of the low dose of ionizing radiation are not thoroughly evident due to an unavoidable increase of occupational exposure and the widespread application of ionizing radiation in medical and industrial fields. The aim of this study was to investigate immune system responses following the low doses of ionizing radiation. BALB/c mice were exposed to Whole Body Irradiation of 20, 50, and 100 mGy through a 60Co source. Lymphocytes extraction were operated 24 h after irradiation. Afterwards, gene expression analysis was performed with relative quantitative Real-Time polymerase chain reaction to IL-4, IFN-γ, and TGF-β expression levels. Moreover, IFN-γ/IL-4 ratio was computed, and the independent sample t-test was performed for the statistical analysis. Whereas IL-4, IFN-γ, and TGF-β expression levels decrease after the radiation of the low doses of gamma rays, the IFN-γ/IL-4 ratio increased significantly after irradiation of 20 mGy (P-Value<0.05). However, this ratio did not vary following the gamma irradiation of 50 and 100 mGy. The positive effects of the low dose of ionizing radiation can be observed through significant alterations in gene expression and the activation of protection mechanisms. This process was caused by the modulation of cellular immune responses after the exposure to 20 mGy. Although the irradiation of higher doses (50 and 100 mGy) induced alterations in the IFN- γ/IL-4 ratio was insignificant. These findings did not confirm the linear no-threshold model theory, and demonstrated that the low dose of ionizing radiation could be the cause of the hormesis phenomenon.

Planning target volume (PTV) is generated from internal treatment volume (ITV) using four-dimensional computed tomography (4D-CT) for enhanced therapeutic gain in the stereotactic body radiotherapy for lung lesions (SBRT-Lung). This study aimed to propose a strategy to generate ITV on multiple-phase 3D-CT and enhance therapeutic gain in SBRT-Lung.
This study was conducted on 6 peripherally located and 5 centrally located lung lesions suitable for SBRT. The PTV was delineated based on 3D-CT datasets acquired at three different phases of respiratory motion. The prescribed dose of 50 Gy in 5 fractions was delivered using RapidArc technique. The therapeutic-gain was compared based on tumor control probability (TCP) and normal tissue complication probability (NTCP) against a multicenter trial, which uses single-phase 3D-CT for PTV delineation. The TCP and NTCP were calculated by Poisson’s linear-quadratic and Lyman-Kutcher-Burman models, respectively.
Regarding the multicentre trial, the PTVs were maximally reduced to 42% and 57% among the 6 peripherally and 5 centrally located lung lesions, respectively. In peripheral lung lesions, TCP was significantly enhanced to 0.6% for long-term (>5years) local control (P<0.05), and NTCP was significantly reduced in pneumonitis (Grade≥II) of lung (0.2%; P<0.05). In central lung lesions, TCP was insignificantly enhanced; however, NTCPs were maximally reduced for cartilage necrosis in trachea (35%) and myelitis in spinal cord (19%).
The proposed strategy reduced the complications for normal tissues and enhanced therapeutic gain. The successful clinical outcomes validated our hypothesis in short-term (6-12 months), and we are currently testing the long-term efficacy.

This study covered the assessment of the natural radioactivity levels and heavy metalsconcentration in dust samples collected from selected schools in the holy Governorate of Karbala. The purpose of thisstudy was to assess the radiological health and safety impact of dust pollution on the children going to school. Sodium Iodide system (NaI [TI])from BICRON and the Atomic Absorption Spectrometer from SHIMADZU were used to measure the natural radioactivity in terms of 238U, 232Th, and 40K, as well as the concentrations of some heavy metals in the dust samples. The specific activity of 238U, Th232, and 40K in dust samples were 5.59± 0.1679 to 71.91±1.6561 Bq/kg, 1.36±0.0963 to 43.35±1.0434 Bq/kg, 66.94±1.638 to 417.91±13.721 Bq/kg, respectively. The external and internal hazard indices were 0.047 ± 0.001 to 0.449±0.011 and 0.062±0.00169 to 0.643±0.01583   respectively. The absorbeddose rate and radium equivalent values ranged from 8.21±0.215 to 76.83±1.968nGy/h and 17.45±0.458to 166.08±4.205 Bq/kg, respectively. The concentration of lead was within the range of 8.839-2.689 mg kg-1 and the concentration of Cd ranged from 0.141 mg kg-1 to less than the lower limit of detection of the Atomic Absorption Spectrometer. The absorbed dose rate, effective dose (indoor and outdoor), hazard indices, and radium equivalent values were within the range of values indicated in the UNSCEAR 2008 report. The levels of lead and cadmium concentration detected in some schools were due to dust pollution in the Schools environment.

The accuracy of dose calculation algorithm (DCA) is highly considered in the radiotherapy sequences. This study aims at assessing the accuracy of five dose calculation algorithms in tissue inhomogeneity corrections, based on the International Atomic Energy Agency TEC-DOC 1583.
A heterogeneous phantom was scanned using computed tomography and tests were planned on three-dimensional treatment planning systems (3D TPSs) based on IAEA TEC-DOC 1583.Doseswere measured for 6- and 18-MV photon beams with ion chambers and then the deviation between measured and calculated TPS doses were reported. The evaluated five DCAs include Monte Carlo (MC) algorithm employed by Monaco, pencil beam convolution (PBC) and anisotropic analytical algorithms (AAA) employed by Eclipse and Superposition (SP), and Clarkson algorithms employed by PCRT3D TPSs.
In Clarkson algorithm, low and high energy photons indicated 7.1% and 14.8% deviations out of agreement criteria, respectively. The SP, AAA, and PBC algorithms indicated 0.9%, 7.4%, and 13.8% for low energy photon and 9.5%, 21.3%, and 23.2% for high energy photon deviations out of agreement criteria, respectively. However, MC algorithm showed 1.8% and less than 1% deviations at high and low energy photons, respectively.
The DCAs had different levels of accuracy in TPSs. Some simple DCAs, such as Clarkson, showed large deviations in some cases. Therefore, the transition to more advanced algorithms, such as MC would be desirable, particularly for the calculation in the presence of inhomogeneity or high energy beams.

The introduction of digital radiography has led to a significant problem in terms of dose creep. To address this problem, manufacturers have established a set of exposure indicators (EI) as a feedback mechanism to safeguard against overexposure. The EI is the measure of incident exposure to the detector that is directly proportional to the signal-to-noise ratio and can be related to image quality. The aim of this study was to evaluate the influence of EI on image quality and radiation dose for the posterior anterior (PA) chest radiography.
This study was conducted in three phases, namely pre-optimization, experimental, and post-optimization. A total of 60 patients that could fulfill the inclusion and exclusion criteria for the PA chest radiography were recruited. The radiographic technical parameters, dose area product, and EI were recorded. Radiographs were printed and evaluated by two recruited radiologists using the modified evaluation criteria established by the Commission of European Communities in 1996.
Statistical analysis using Spearman’s Rho Correlation showed an insignificant relationship between EI and image quality for the PA chest radiography (P>0.05). Conversely, there was a significant relationship between EI and radiation dose (P<0.05).
TheEI can be used as an indirect measure of image quality and radiation dose. The EI does not directly determine image quality since the radiographic technique and parameters used can affect image quality. Although EI can be used as a measure of radiation dose, it cannot provide an accurate measurement of the radiation received by the patient.

Low-pass filters eliminate noise, and accordingly improve the quality of filtered back-projection (FBP) in the reconstruction of single photon emission computed tomography (SPECT) images. This study aimed at selection of an optimum low-pass filter for FBP reconstruction of SPECT images of small structures.
Spheres A, B, and C (16 mm, 12 mm, and 11 mm in diameter, respectively) attached to capillary stems were filled with technetium-99m solution (activity concentration 300 kBq/mL). They were then mounted inside a Jaszczak Phantom forming a V-shaped structure. The phantom was then filled with distilled water. Two-dimensional (2D) projections were acquired on 128 128 pixels using a Siemens E-Cam dual-head gamma camera. The Parzen, Shepp-Logan, Low Pass Cosine filters (cut-off frequencies: 0.2-0.9), and Butterworth filter (order: 1-9; cut-off frequencies: 0.3-0.9) were employed during FBP reconstruction. The line command of ImageJ software was used to draw the point spread functions of acquired 2D transaxial central slices and for the measurement of their full-width at half-maximum (FWHM).
The FWHM of 2D central image slices of spheres A, B, and C reconstructed using a Butterworth filter measured 20, 20, and 10 pixels, respectively. In comparison, the reconstructed images using the Parzen, Low Pass Cosine, and Shepp-Logan filters measured to 27, 25 and, 22 pixels for sphere A, 24, 22, 20 pixels for B, and 22, 20, 18 pixels for C, respectively.
The low-pass filters successfully suppressed noise during the FBP reconstruction of SPECT images of small structures. Accordingly, the Butterworth is a suitable choice.

Although travertine is now widely used as a building material, the effects of its radiological hazards to public health should be a matter of concern. Therefore, this study aimed to determine its radiological parameters with regard to human health. In this research 10 travertine samples were collected from exploitation zone in Haji Abad Mine in Mahallat, Iran. Specific radionuclide activities were determined by gamma spectrometry using a high purity germanium detector. In addition, radiological parameters, such as radium equivalent, air doses, internal and external risk factors (Hin, Hex), yearly gonadal dose equivalent (AGDE), and additional cancer risk (ELCR) throughout life were calculated. The specific activities of 226Ra, 232Th, and 40K radionuclides ranged within 3.08-9.16, 1.22-6.45, and 20.15-91.04 Bq/kg, respectively. The obtained means of internal and external annual effective dose of samples were 0.03 and 0.007 mSv/y. External and internal hazard indices for samples were within the range of 0.003-0.01 and 0.01-0.03, respectively. The results of this study show that the amount of radionuclides in travertine rocks is very small compared to its global average in soil and rock. Therefore, it is suggested to use travertine as a building material, which is not a threat to public health.

Skin cancer has been increased day by day, but it can be cured if it diagnosed early. After reviewing the scientific literature about 980 nm diode laser, and its multiple advantages on skin diseases. We studied in this paper the effectiveness of this type of laser on the progression of skin cancer among hamsters which were exposed to carcinogen on the back. The carcinogenic solution of 9, 10-dime thy 1-1, 2-benzanthracene was applied to the hamsters' skin on the back. A 980 nm Diode laser light with irradiation power of 0.5w and 1.0w and an exposure time of 100 sec were used in order to prevent the harmful thermal effect on surrounding tissue as studied in previous paper [1]. According to the results, only one group of hamsters which was not consistently irradiated by laser gave rise to melanoma tumor. The other groups that were exposed to diode 980nm laser irradiation at different powers (i.e., 0.5w and 1.0w) and an exposure time of 100 sec showed no growth of skin cancer during the experiment. The 980 nm Diode laser has an effect on delaying the onset of cancer and has had a role in the reduction of skin cancer lesions. However, further studies are required to test its inhibitory activities against carcinogenesis.