Iranian Journal of Medical Physics
Volume:15 Issue: 4, Autumn 2018

Brain visual evoked potential (VEP) signals are commonly known to be accompanied by high levels of background noise typically from the spontaneous background brain activity of electroencephalography (EEG) signals.
Material and A model based on dyadic filter bank, discrete wavelet transform (DWT), and singular value decomposition (SVD) was developed to analyze the raw data of visual evoked potentials and extract time-locked signals with external visual stimulation. A bio-amplifier (iERG 100P) and data acquisition system (OMB-DAQ-3000) were utilized to record EEG raw data from the human scalp. MATLAB Data Acquisition Toolbox, Wavelet Toolbox, and Simulink model were employed to analyze EEG signals and extract VEP responses. Results were verified in Simulink environment for the real recorded EEG data. The proposed model allowed precise decomposition and classification of VEP signals through the combined operation of DWT and SVD. DWT was successfully used for the decomposition of VEP signals to different frequencies followed by SVD for feature extraction and classification. The visual and quantitative results indicated that the impact of the proposed technique of combining DWT and SVD was promising. Combining the two techniques led to a two-fold increase in the impact of peak signal to noise ratio of all the tested signals compared to using each technique individually.

In recent years, modern microscopic imaging in parallel with digital image processing techniques, have facilitated computerized semen analysis. However, in these methods, distinguishing sperms from other semen particles can be hampered by low contrast of microscopic images and the possibility of neighboring sperms touching each other. This article introduced a new method based on combination of Zernike moments and spatial processing in sperm detection. In the first step, Zernike moments were estimated due to their rotation and noise-resistant nature to mark pixels with some chance of belonging to sperms. In the second step, pruning was executed considering the connectivity of candidates and using morphological processing, to extract sperms. The proposed algorithm was examined on microscopic images exhibiting several sperms with different morphologies. The obtained results showed the ability of the proposed method in sperm detection, such that it could detect 85% of the sperms without any false detection. In a more pragmatic situation, where false detection rate was 5%, the detection rate of the proposed algorithm increased to 94%. Comparing the proposed method with watershed segmentation algorithm (WSA) and morphological contour synthesis (MCS) revealed the superiority of the proposed method to its alternatives in such a way that it detected sperms at least 3% and 13% better than WSA and MCS, respectively, without any false detection. Furthermore, the rate of false detections in the proposed algorithm was at least 4% and 14% better than its alternatives.

Nowadays, X-ray radiographic imaging plays an essential role in disease diagnosis and treatment. In addition to benefits, X-rays have harmful effects for both patients and radiographers. Observing radiation protection principles reduces radiation exposure and the probability of radiation risk. Therefore, we sought to assess the knowledge, attitude, and performance of radiographers in this regard.
Material and This descriptive and analytic study was performed in South Khorasan Province in 2017. Data collection was performed by using a questionnaire containing items on knowledge, attitude, and performance. By using the census sampling method, 100 radiographers and senior radiology students were enrolled. To analyze the data, descriptive statistics were used in SPSS, version 20. The mean scores of knowledge, attitude, and performance were 61.8±13.8, 67.4±21.5, and 50.7±18.4, respectively. Gender had no significant effect on the radiographers' knowledge, attitude, and performance. The level of education was not significantly related to performance, while it had a significant direct association with knowledge and attitudes of the participants. Considering the knowledge, attitude, and performance scores of the radiographers and their willingness to attend retraining courses, we recommend holding such courses. It seems that these courses could be very effective in improving the knowledge, attitude, and performance of radiographers towards the principles of radiation protection.

In recent years, the number of computed tomography (CT) scans, which is a high-dose technique, has increased significantly. Head and neck CT is performed frequently and thyroid, particularly in children, has always been considered a sensitive organ. In recent years, radiobiologists and health physicists have been more concerned about the safety of lenses of the eyes, as cataract is no longer considered a deterministic effect.
Material and In the present study, incurred doses to the thyroid and lens of the eye of 140 patients who underwent common head and neck CT at five hospitals were measured by thermoluminescent dosimeters (TLD-100). The patients were divided into two age groups of pediatrics and adults. TLD chips were placed on the patient’s skin surface. For each patient, scan parameters, sex and age were recorded. Exposed TLDs were read by a manual TLD reader. The verage absorbed dose of the thyroid, as well as the lenses of the left and right eyes were 5.89±1.74, 15.84±2.81 and 16.25±2.57, respectively, for the pediatric patients and 5.00±1.17, 17.64±1.69 and 24.41±1.89 for adults. Patient-specific organ doses were influenced by the scanned region, scan protocol and patient's age. In the present study, the mean eye dose was much lower than the 500 mGy threshold recommended by International Commission on Radiological Protection (ICRP) for lens of the eye damage, thus, it appears to be clinically safe. While CT scan remains a crucial tool, further dose reduction can be achieved by controlling different factors affecting patient doses.

Craniospinal radiotherapy is a therapeutic technique for central nervous system (CNS) tumors, which requires meticulous attention to technique and dosimetry.Treatment planning system (TPS) is one of the main equipment in radiotherapy; therefore, the evaluation of its accuracy is essential for dose calculation. The present study evaluates the validity of Isogray TPS in craniospinal irradiation techniques.
Material and The computed tomography (CT) images of the brain and spine of the Rando phantom were acquired. Two techniques were designed. In technique 1, the whole CNS was irradiated with 6 MV photon beam. In technique 2, the brain and spine were irradiated with 6 MV photon and 18 MeV electron beam, respectively. The tumor and organs at risk doses were measured by thermoluminescent dosimeter (TLD). In addition, photon and electron dose measurements inside and outside the treatment field were accomplished using TLD, and then compared to the corresponding values calculated by TPS. According to the results, in both electron and photon beams, the differences between the doses calculated by TLD and TPS for the points inside the treatment field were less than 4% for 90% of the measurement points. However, for the points outside the treatment field borders, the differences ranged within 10-40%. These differences were indicative of the sufficient dosimetric accuracy of Isogray TPS. The comparison of dosimetry results with those of TPS results revealed the accuracy of Isogray TPS. In both techniques, the maximum difference between the TLD- and TPS-measured doses was observed in the mandible.

Reduction of peak kilovoltage (kV) setting has been a useful approach to d creating radiation dose; however, it may have varied effects on noise and the accuracy of diagnosis. Thus, we compared image quality between low (80 kV) and standard kilovoltage (100 kV) protocols.
Material and This triple blind non-randomized parallel quasi-experimental study was conducted on 140 cases of questionable pulmonary embolism. Image quality was twice as high as the standard protocol in the 80-kV group (odds ratio=2.08). Main, segmental, and subsegmental arteries showed significantly higher vascular enhancement (P<0.001) in the 80-kV group. Similarly, the mean number of measurable segmental arteries was significantly greater in the 80-kV group relative to the standard group. On the other hand, the mean of image noise was significantly higher in the 80-kV group in comparison with the 100-kV group (mean: 68.4 vs. 43.1; P<0.001). Finally, the mean of radiation dose received in the 80-kV group was significantly lower than that in the 100-kV group (mean: 0.94 vs. 2.43 mSv; P<0.001). Lower radiation dose received and higher image quality, but worse image noise, in the 80-kV group compared to the 100-kV group present acceptable evidence in support of reduction of voltage in cases with the suspicion of pulmonary embolism. In these patients, therefore, it is recommended as a good strategy to be adopted in computed tomography angiography.

According to the literature, optical coherence tomography (OCT) can be used measure radiation absorbed dose. This study was carried out to design a computed tomography system for the calculation of absorbed dose and optimization of dose delivery in radiotherapy using gel dosimeters.
Material and An advanced charge-coupled device based OCT system was developed in laboratory with the capability for high resolution three-dimensional (3D) radiation dosimetry using gel dosimeters. The OCT system was compared to magnetic resonance imaging (MRI) as a standard system to investigate its accuracy. Additionally, a number of parameters were checked for assessing the performance of the system. Developing an advanced OCT system, the calibration curve was drawn for OCT and MRI and the received dose values were compared. The amounts of dose obtained from OCT and MRI were 1.98 and 2 Gy respectively with a relative difference of 2%. The quality of treatment can be improved using OCT system in radiotherapy dosimetry.

Environmental and occupational human exposure from neutron source can lead to the serious biologic effects. The aim of this study is to evaluate the cancer incidence risk for various human organs at different neutron dose levels due to exposure from an Americium-241/Beryllium (Am-241/Be), a standard neutron source for calibration purposes.
Material and We measured ambient dose equivalent H*(10) at different distances from Am-241/Be mixed neutron source by Berthold LB 6411 detector and determined cancer incidence risk for different organs of both male and female subjects at different neutron exposure levels by BEIR VII model. Exposure age had a reverse impact on cancer incidence risk of different organs. We found that as H*(10) increases, cancer incidence risk increments as well. Colon (for men) and bladder (for women) had the highest sensitivity to neutron exposure, while prostate and uterus showed the lowest risk of cancer incidence among male and female subjects, respectively. Older exposed persons are at a lower risk of cancer incidence. The risk of cancer incidence for various organs is considerably associated with gender, such that radiation sensitivity of female organs was higher at all the measured neutron dose levels.

Introduction: Silicone gel breast implants are used for breast reconstruction post mastectomy. In the event of cancer recurrence, the radiation oncologists are forced to irradiate through the prosthesis device. Due to prosthesis higher atomic number dose perturbations occur during treatment. This study determined the influence of silicone gel thickness on the photon beam distribution. A Varian linear accelerator, water phantom (dimensions 30 × 30 × 30 cm3), silicone gel breast prosthesis and Omni-Pro Accept software were used in the study. With the gantry positioned at at a source-to-surface distance (SSD) of 100 cm, the collimators were adjusted to a field size of 10 × 10 cm2 and the 6 MeV photon beam was used. Omni-Pro Accept software was used to plot the percentage depth dose curves and the beam profiles. The results obtained with a Monte Carlo Nuclear Particle (MCNP) Code were validated with the measurement data. The beam profile and percentage depth dose curves were also measured for silicone gel thicknesses (4, 6, 8, 10, 12, 14 and 16 cm) and width 16.5 cm aligned 1 cm below the surface of the water. The measured and calculated percentage depth dose (PDD) ratio was 0.03. The measured and calculated beam profiles were 0.5% and 0.9% respectively. For the silicone gel prosthesis, the depth dose values at 0.5 cm below the prosthesis were 2.8%. Dose perturbations below the breast prosthesis are insignificant, breast prosthesis are safe in the event of carcinoma recurrences.

Electrochemotherapy (ECT) is a cancer treatment modality to permeabilize cell membrane facilitating the non-permeant molecules to gain access to the cytosol of cells. Nevertheless, environmental electromagnetic fields (EMFs) may disturb the efficiency of ECT. The present study aimed to investigate the effect of EMFs 900 MHz pulse-modulated by 217 Hz extremely low-frequency fields on the efficiency of ECT The 4T-1 cells were exposed to 900 MHz radiofrequency (RF) modulated by 217 Hz fields at the power densities of 17, 162, and 349 µW/cm2 (related to antenna input powers of 3, 4, and 5 W at a distance of 15 cm) by a GSM900 MHz simulator. After exposure, the cells were divided into several groups, receiving no treatment, chemotherapy, electric pulse, and ECT. The cell viability was evaluated by MTT assay after 24 h. The results demonstrated that 900 MHz RF pulse-modulated by 217 Hz EMF at 349 µW/cm2 increased the viability of the cells treated with EPs with the amplitude of 70 V/cm and frequency of 5 kHz (16%), ECT with 70 V/cm at 5 kHz (20%), and ECT with 60 V/cm at 5 kHz (16%), compared to their counterpart treatment group with no exposure. However, the fields had no significant effect on the efficacy of chemotherapy. As the findings of the current study indicated, environmental pulsed-modulated RF fields exerted an adverse influence on some antitumor therapies. Therefore, such effects should be taken into consideration in determining the optimal protocols of treatment.

Phantom studies facilitate the implementation of radiation dose surveillance as a function of radiographic technical parameters for minimizing patient radiation dose. The evidence of such investigations can then be used to evaluate technical parameters used in the radiographic procedures to reduce radiation dose without compromising the image quality.
Material and This experimental study was carried out using an anthropomorphic phantom and the Leeds test object. Computed radiographic system was utilized and the images were printed for objective evaluation. Dose-area-product (DAP) readings were obtained using a DAP meter for the technical parameters employed for the radiographic procedures. The use of 0.2 mm additional copper filtration resulted in the lowest radiation doses for all four radiographic procedures (i.e. posteroanterior chest, anteroposterior abdomen and lumbar sacral spine projections). The highest tube potential appropriate to the body part being imaged, patient size, image receptor response and required information resulted in the minimum radiation dose to the patient without compromising the image quality. The focus to film distance utilized for the radiographic procedure must be in accordance with the focus to grid distance specified by the manufacturer when using the bucky to eliminate grid “cut-off.” The optimization of image quality and radiation dose can be accomplished by using a phantom and selecting the imaging parameters that yield an acceptable image quality with the lowest entrance surface dose while considering the adjustment for patient size.

Endovenous laser treatment (ELT) is a new treatment method for the reflux of the great saphenous vein. A successful ELT is dependent on the selection of optimum parameters required to achieve optimal vein damage while avoiding side effects including skin burns. The mathematical modeling of ELT can be used to understand the process of ELT. This study was conducted to examine the effect of laser pullback speed and the distance between the vein and skin on the performance of ELT.
Material and The finite element method was used to develop optical-thermal damage models and simulate the process of ELT process. Firstly, light distribution was modeled using the diffusion approximation of the transport theory. On the second step, temperature rise was determined by solving the bioheat equation. Considering the temperature field, the extension of laser-induced tissue damage was estimated using Arrhenius model. Regarding the results, pullback speed and the distance between the vein and the skin distance can affect the process of ELT. Moreover, the pullback speed of 1 mm/s, 2 mm/s, and 4mm/s were suitable for the treatment of varicose veins located in a depth of 15 mm, 10 mm, and 5 mm, respectively. In the ELT method, the pullback speed should be determined considering the geometry of the varicose vein segments, especially the distance between the skin and vein.

After the lead poisoning outbreak came to light in Zamfara State, Nigeria, people living near gold mines were worried about environmental safety, especially drinking water quality. This study examined the gross alpha and gross beta activity concentrations in groundwater in different locations of Anka, Zamfara State, Nigeria, to measure the possible radiation dose and potential health effects.
Material and In this study, 32 water samples were collected from hand dug wells and boreholes in Anka, Nigeria, through stratified random sampling method. The ISO 9696 and ISO 9697 methods were adapted using Eurysis system-multiple-channel-gas-filled proportional counter to measure gross alpha and gross beta activity concentration. The ranges of alpha and beta activity concentration in groundwater of the area were 0.114 to 3.698 Bq/l and 0.071 to 4.823 Bq/l with the geometric means of 0.961 Bq/l and 2.134 Bq/l, respectively. These amounts were higher than the reference limits of 0.5 Bq/l and 1 Bq/l for gross alpha and beta activity concentrations, respectively. Additionally, the total annual effective dose equivalent was more than that (0.1 mSv/y) of recommended by World Health Organization (WHO). The mean concentrations of alpha and beta activities in the samples were above the limits recommended by WHO. These excessive radiations might negatively affect the environment and inhabitants.

Electronic portal imaging devices (EPIDs) provide two- and three-dimensional planar and volumetric cone beam images to improve the accuracy of radiation treatment delivery. Periodic quality assurance (QA) of EPIDs is essential for dosimetric verification in radiotherapy. In this study, a QA program was implemented to evaluate the function of the EPID to be confident in applying corrections for the uncertainty of patient set-up.
Material and Firstly, the safety features were verified, and the uniformity of EPID response was evaluated using flat panel detector. Additionally, the contrast and spatial resolutions of the EPID were assessed using detail counting of the Los Vegas phantom images by visualization method and measuring the modulation transfer function using edge technique, respectively. Moreover, a combination of smoothing methods was used for optimal use of edge detection algorithm for the noisy portal images. Finally, the location of the central ray on the EPID surface at different gantry angles was determined to evaluate the mechanical stability of the supporting arm. The safety interlocks were found to be functional.The EPID response variation was less than 3% according to the results obtained from the detector. The contrast resolution met the recommended tolerance; however, the visualization method was widely observer-dependent. The value of f50 for spatial resolution was 0.401±0.005 lp/mm for the photon energy of 6 MV. The supporting arm deviation was within ±1 mm. The periodic QA of image guidance system gave confidence to apply the corrections for set-up in clinic.

Megavoltage X-ray beams are used to treat cervix cancer due to their skin-sparing effect. Preferably, the radiation surface doses should be negligible; however, it increases due to electron contamination produced by various field parameters. Therefore, it is essential to provide proper knowledge about the effect of different field parameters on radiation doses. This study sought to find out the effect of various physical parameters on the surface doses. The effects of field size, source-to-surface distance, and open or acrylic block tray fields on surface doses were determined. Metal-Oxide-Semiconductor-Field-Effect-Transistor based dosimetric system was used for dose measurements for 6 MV photon beam. The directly measured radiation surface doses on pelvic phantom were compared to surface dose values computed by treatment planning system in the similar field parameters. The measured results for the percentage depth dose (PDD0) in field size of 10x10 cm2 were 13.32%, 12.95% and 13.87% for open field and 36.87%, 36.31% and 35.88% for acrylic block tray field. In addition, the computed doses were 7.83%, 7.73% and 7.65% for open field and 16.33%, 16.12% and 15.88% for acrylic block tray field at 80 cm, 100 cm, and 120 cm SSDs, respectively. The surface dose increases along with the size of the field and decreases with increasing SSD. The surface doses in acrylic block tray fields were significantly higher than the open ones. The treatment planning system computed a lesser radiation doses in same field parameters.

The most important limitation of 5-aminolevulinic acid (5-ALA)-induced photodynamic therapy (PDT) is the efficacy of the cells in converting 5-ALA to protoporphyrin IX. The present study aimed to investigate the effectiveness of silver nanoparticles (AgNPs) with the photosensitivity at the surface plasmon resonance wavelength on 5-ALA-mediated PDT.
Material and First of all, the toxicity of 5-ALA, AgNPs, and combined 5-ALA and AgNPs was evaluated on DFW cell line derived from melanoma. After choosing the optimal concentration, both pulsed and continuous light irradiations were conducted at different doses using a light‑emitting diode source in the groups receiving 5-ALA, AgNPs, as well as 5-ALA and AgNPs combination, and the controls. The cell survival was evaluated 24 h after irradiation using MTT assay. According to the results, light exposure did not significantly change cell survival in the absence or presence of AgNPs. However, light exposure in the presence of 5-ALA and AgNPs/5-ALA combination caused a significant reduction in the cell survival. The necessary light exposure to induce 50% cell death (ED50) in the presence of 5-ALA was 1280 mJ/cm2; however, this value was 280 mJ /cm2 in the presence of combined AgNPs and 5-ALA. As the findings indicated, PDT had a higher efficacy in the presence of combined 5-ALA and AgNPs than in the sole 5-ALA presence. Nonetheless, further studies are required to evaluate the definitive mechanism of these findings.