Iranian Journal of Medical Physics
Volume:13 Issue: 4, Autumn 2015

One of the central questions in radiological protection is the magnitude of the risks from low doses of radiation, related to the justification and optimization of the diagnostic medical exposures. Therefore, the aim of this study was to estimate the cancer incidence and mortality risks in children of different ages, sizes, and ethnicities undergoing computed tomography examinations.
In this study, the risk estimations were performed, using the organ dose data of 16 pediatric voxel phantoms obtained in our previous publications. In addition, we employed the risk models recommended by the committee of biological effects of ionizing radiation for all solid cancers, leukemia, and cancers of several specific sites. Linear interpolation was also applied for the risk estimations of different ages.
According to the results of this study, there are significant differences between the cancer risks for some organs even in the phantoms of the same age. Therefore, it was concluded that using the reference data for all children with anatomical discrepancies would lead to under- or overestimation of the risk values. In addition, only the amount of dose cannot be the appropriate representative of the risk, and parameters like size, age, and gender might have direct impacts on cancer incidence and mortality risks.
The findings of the current study are useful to update the information about the individual and the long-term collective public health risks.

Quantitative susceptibility mapping (QSM) is a new contrast mechanism in magnetic resonance imaging (MRI). The images produced by the QSM enable researchers and clinicians to easily localize specific structures of the brain, such as deep brain nuclei. These nuclei are targets in many clinical applications and therefore their easy localization is a must. In this study, we aimed to implement two QSM estimation algorithms, threshold-based k-space division (TKD) and morphology enabled dipole inversion (MEDI) in presurgical planning.
In this study, susceptibility weighted imaging (SWI) was performed on six patients referred to our center for presurgical planning purposes. The susceptibility values, as well as the contrast-to-noise ratio of few brain regions were estimated. To identify the algorithm, which was best applicable to clinics, a comparison of the two methods was performed.
QSM images were produced; however, the results did not show any significant differences between the susceptibility values of the two methods. The contrast-to-noise ratio for the susceptibility values of the subthalamic nucleus and substantia nigra brain regions were significantly superior using the MEDI approach over TKD, suggesting improved localization of brain regions using the former method.
This study suggests that to identify specific brain regions, such as deep brain nuclei, a QSM contrast would be more beneficial than the conventional MRI contrasts. This study compared MEDI and TKD methods for quantification of brain susceptibility maps, and results showed that the MEDI method resulted in higher-quality images.

Accurate estimation of the skin-absorbed dose in external radiation therapy is essential to estimating the probability of secondary carcinogenesis induction
Electron contamination in prostate radiotherapy was investigated using the Monte Carlo (MC) code calculation. In addition, field size dependence of the skin dose was assessed. Excess cancer risk induced by electron contamination was determined for the skin, surface dose, and prostate dose-volume histogram (DVH) using MC calculation and analytical methods.
MC calculations indicated that up to 80% of total electron contamination fluence was produced in the linear accelerator. At 5 mm below the skin surface, surface dose was estimated at 6%, 13%, 27%, and 38% for 5×5 cm2, 10×10 cm2, 20×20 cm2, and 40×40 cm2 field sizes, respectively. Relative dose at Dmax was calculated at 0.92% and 5.42% of the maximum dose for 5×5 cm2 and 40×40 cm2 field sizes, respectively. Excess absolute skin cancer risk was obtained at 2.96×10-4 (PY) -1 for total 72 Gy. Differences in prostate and skin DVHs were 1.01% and 1.38%, respectively.
According to the results of this study, non-negligible doses are absorbed from contaminant electrons by the skin, which is associated with an excess risk of cancer induction.

Globally, the need for radiotherapy as a part of cancer management increases every year. Thus, the shielding for megavoltage radiotherapy rooms is of great importance.
In the present study, 14 types of developed high-density concrete with densities ranging from 2.45 to 5.11 were simulated by using Monte Carlo method. The linear attenuation coefficient and the tenth value layer were also calculated. These dosimetric parameters were investigated for megavoltage photon beam spectra for various energies (4, 6, 10, 15, and 18 MeV) of the Varian linac and 60Co gamma rays. The results of simulation were compared with the available published results.
The results showed that the attenuation of high-energy photons is primarily administered by the atomic number and density of the concrete. Moreover, the variation of attenuation coefficient with density was not completely linear.
It was concluded that the attenuation of high-energy photons not only depends on the density of concrete, but also on the atomic number of its composing elements. dependent on density of concrete but also on atomic number of composing elements.

Breast cancer is the second cause of mortality among women. Early detection of it can enhance the chance of survival. Screening systems such as mammography cannot perfectly differentiate between patients and healthy individuals. Computer-aided diagnosis can help physicians make a more accurate diagnosis.
Regarding the importance of separating normal and abnormal cases in screening systems, a hierarchical classification system is defined in this paper. The proposed system is including two Adaptive Boosting (AdaBoost) classifiers, the first classifier separates the candidate images into two groups of normal and abnormal. The second classifier is applied on the abnormal group of the previous stage and divides them into benign and malignant categories. The proposed algorithm is evaluated by applying it on publicly available Mammographic Image Analysis Society (MIAS) dataset. 288 images of the database are used, including 208 normal and 80 abnormal images. 47 images of the abnormal images showed benign lesion and 33 of them had malignant lesion.
Applying the proposed algorithm on MIAS database indicates its advantage compared to previous methods. A major improvement occurred in the first classification stage. Specificity, sensitivity, and accuracy of the first classifier are obtained as 100%, 95.83%, and 97.91%, respectively. These values are calculated as 75% in the second stage
A hierarchical classification method for breast cancer detection is developed in this paper. Regarding the importance of separating normal and abnormal cases in screening systems, the first classifier is devoted to separate normal and tumorous cases. Experimental results on available database shown that the performance of this step is adequately high (100% specificity). The second layer is designed to detect tumor type. The accuracy in the second layer is obtained 75%.

Artificial and natural radionuclides are found in diverse environmental compartments, such as water, soil, rocks, vegetables, animals, and human body tissues. As such, humans and environments are at constant exposure of these radiation types. In this research investigated specific activities of radionuclide and dose assessment of some species of mushrooms.
In this study, natural and artificial radioactivity concentrations were determined in Agaricus bispora (nourished mushrooms), Cantharellus cibarius, Coprinus micaceus (wild fungi species) and their composts through gamma-ray spectrometryusinga high-purity germanium (HPGe) detector with 30% relative efficiency.
Radioactivity concentrations of 238U and 232Th in edible mushroom samples were lower than the minimum detectable activity (MDA). For 40K and 137Cs, these concentrations were within the ranges of 1895.24-1920.24and Results of this study showed that the radioactivity concentrations of edible mushrooms are close to or lower than MDA. In addition, radioactivity concentrations of the composts were indicative of the low pollution of the studied regions by radiocesium. Annual consumption rate threshold was calculated as 26.7 kg in dry weight (fresh weight: 267 kg). Therefore, it could be concluded that consumption of these mushrooms is associated with no health consequences for consumers.

Patient set-up optimization is required in radiotherapy to fill the accuracy gap between personalized treatment planning and uncertainties in the irradiation set-up. In this study, we aimed to develop a new method based on neural network to estimate patient geometrical setup using 4-dimensional (4D) XCAT anthropomorphic phantom.
To access 4D modeling of motion of dynamic organs, a phantom employs non-uniform rational B-splines (NURBS)-based Cardiac-Torso method with spline-based model to generate 4D computed tomography (CT) images. First, to generate all the possible roto-translation positions, the 4D CT images were imported to Medical Image Data Examiner (AMIDE). Then, for automatic, real time verification of geometrical setup, an artificial neural network (ANN) was proposed to estimate patient displacement, using training sets. Moreover, three external motion markers were synchronized with a patient couch position as reference points. In addition, the technique was validated through simulated activities by using reference 4D CT data acquired from five patients.
The results indicated that patient geometrical set-up is highly depended on the comprehensiveness of training set. By using ANN model, the average patient setup error in XCAT phantom was reduced from 17.26 mm to 0.50 mm. In addition, in the five real patients, these average errors were decreased from 18.26 mm to 1.48 mm various breathing phases ranging from inhalation to exhalation were taken into account for patient setup. Uncertainty error assessment and different setup errors were obtained from each respiration phase.
This study proposed a new method for alignment of patient setup error using ANN model. Additionally, our correlation model (ANN) could estimate true patient position with less error.

H istone deacetylase inhibitors (HDIs), as radiation sensitizing agents, are considered as a novel class of anti-cancer factors, which are studied in various tumor cell-lines. Valproic acid (VPA) is an HDI, which is effectively used in the treatment of epilepsy, migraines, and some particular types of depression. In this study, we evaluated the effects of VPA and ionizing radiation separately, as well as combined, with the alterations of histone H2AX phosphorylation (γH2AX) at Ser139, a marker of DNA damage and its repair, on MCF-7 breast cancer cell line.
Three groups of cells were selected, including 1) pretreated with VPA for 48 h followed by irradiation, 2) VPA only, and 3) irradiation only. The levels of γH2AX expression were evaluated using Western blot.
The results of our study showed that VPA signifi­cantly enhanced the expression of γH2AX, when applied 48 h prior to irradiation compared to the IR or VPA only treated cells. We also concluded that VPA pre-treatment delayed γH2AX dephosphorylation and dispersal for up to 12 h after irradiation, while γH2AX dephosphorylation disappeared in just 2 h when using irradiation alone and without VPA pre-treatment.
Our findings are consistent with the general consensus that VPA efficiently sensitizes cancer cells to the effects of ionizing radiation and prevents DNA double-strand break repair, which leads to enhanced breast cancer cell death.