Showing papers in "Iranian Journal of Medical Physics in 2015"

The Evaluation of Conventional X-ray Exposure Parameters Including Tube Voltage and Exposure Time in Private and Governmental Hospitals of Lorestan Province, Iran

Abstract: Introduction In radiography, dose and image quality are dependent on radiographic parameters. The problem is caused from incorrect use of radiography equipment and from the radiation exposure to patients much more than required. Therefore, the aim of this study was to implement a quality-control program to detect changes in exposure parameters, which may affect diagnosis or patient radiation dose. Materials and Methods This cross-sectional study was performed on seven stationary X-ray units in sixhospitals of Lorestan province. The measurements were performed, using a factory-calibrated Barracuda dosimeter (model: SE-43137). Results According to the results, the highest output was obtained in A Hospital (M1 device), ranging from 107×10-3 to 147×10-3 mGy/mAs. The evaluation of tube voltage accuracy showed a deviation from the standard value, which ranged between 0.81% (M1 device) and 17.94% (M2 device) at A Hospital. The deviation ranges at other hospitals were as follows: 0.30-27.52% in B Hospital (the highest in this study), 8.11-20.34% in C Hospital, 1.68-2.58% in D Hospital, 0.90-2.42% in E Hospital and 0.10-1.63% in F Hospital. The evaluation of exposure time accuracy showed that E, C, D and A (M2 device) hospitals complied with the requirements (allowing a deviation of ±5%), whereas A (M1 device), F and B hospitals exceeded the permitted limit. Conclusion The results of this study showed that old X-ray equipments with poor or no maintenance are probably the main sources of reducing radiographic image quality and increasing patient radiation dose.

Quality Control of Conventional Radiology Devices in Selected Hospitals of Khuzestan Province, Iran

Abstract: Introduction Quality control techniques used to test the components of the radiological system and verify that the equipment is operating satisfactorily. In this study, quality control (QC) assessment of conventional radiology devices was performed in frequently visited radiology centers of Khuzestan province, Iran. Materials and Methods Fifteen conventional radiology devices were examined, based on the protocol proposed in Report No. 77 by the Institute of Physics and Engineering in Medicine (IPEM). Ten standard QC tests, including voltage accuracy and reproducibility, exposure time accuracy and reproducibility, tube output linearity (time and milliampere), filtration (half-value layer), tube output (70 kV at FSD =100 cm), tube output reproducibility and beam alignment were performed and assessed. All measurements were performed, using Barracuda multi-purpose detector. Results The reproducibility of voltage, exposure time and dose output, as well as output linearity, met the standard criteria in all devices. However, in 60% of the units, the results of the beam alignment test were poor. We also found that 66.7% of the studied units offer services to more than 18,000 patients annually or 50 patients per day. Conclusion Despite the fact that radiological devices in Khuzestan province are relatively old with high workload, the obtained results showed that these devices met the standard criteria. This may be mainly related to proper after-sale services, provided by the companies. Although these services may be expensive for radiology centers, the costs may be significantly reduced if QC is defined as a routine procedure performed by qualified medical physicists or radiation safety officers.

Evaluation of Organ and Effective Doses to Patients Arising From Some Common X-Ray Examinations by PCXMC Program in Sabzevar, Iran

Abstract: Introduction The purpose of this study was to estimate organ and effective doses in patients undergoing some common X-ray examinations in Sabzevar, Iran. The effective dose is one of the best parameters for describing the amount of radiation dose received by a patient undergoing any diagnostic X-ray examination. The public dose from X-ray examinations depends on various factors, and its contribution to the overall public dose from medical applications widely varies in different societies; however, in Iran, limited data is available on this subject. Materials and Methods In the present study, we aimed to estimate organ and effective doses arising from some common X-ray examinations on patients. Organ and effective doses were calculated by employing PCXMC program, based on Monte Carlo method. Results The mean effective doses in this study were compared with similar findings reported in previous research. The applied methods in different studies are the main factors, which influence the effective dose values. Conclusion Radiation doses to radiosensitive organs such as the ovaries, testicles, and thyroid may induce harmful effects, e.g., cancer and genetic effects. Therefore, we should try to maintain the organ doses as low as possible.

Evaluation of the Level of Protection in Radiology Departments of Kermanshah, Iran

Abstract: Introduction Radiation protection is an important safety issue for radiographers and patients. The aim of this study was to assess the observance of radiation protection regulations in radiology departments of Kermanshah University of Medical Sciences, Kermanshah, Iran. Materials and Methods In total, 48 radiographers and 8 radiography rooms were evaluated in three hospitals of Kermanshah, Iran. Additionally, 120 patients were randomly selected in the present study. For data collection, a questionnaire on radiation protection devices, radiographers, and patients was completed. Data were analyzed, using Microsoft Excel. Results Based on the analysis, 56.8% of radiation protection devices were accessible to radiographers. Overall, 81.3% of radiographers stated that they utilized film badges for radiographic procedures, while only 71.7% had used these badges in practice. Additionally, 54.2% of radiographers claimed that they regularly performed medical check-ups; however, based on the documents available at personnel offices, only 43.8% had taken this measure into account. Also, 60.4% of radiographers claimed that they had participated in annual training courses, while based on the records, only 41.7% had participated in such courses. Conclusion The majority of radiographers had no regard for radiation protection principles for either themselves or the patients. Apparently, not only hospital authorities, but also heads of departments ignore radiation protection principles for the patients and radiographers.

A Study on Transfer Factors of Environmental Radionuclides: Radionuclide Transfer from Soil to Different Varieties of Rice in Gorgan, Iran

Abstract: Introduction Natural and artificial radionuclides are the main sources of human radiation exposure. These radionuclides, which are present in the environment, can enter the food chain. Rice is one of the most important food components in Iran. Radionuclides by transferring from soil to rice and entering the human body can affect human health. Materials and Methods Fourteen samples of different varieties of rice, nine soil samples from rice fields and four samples of consumed water were collected from four villages around Gorgan, Iran. Specific activities of 226Ra, 232Th, 40K and 137Cs were determined in the samples, using gamma ray spectrometry and a high-purity germanium (HPGe) detector. Moreover, transfer factors of radionuclides from soil to rice were determined. Results Specific activities of 226Ra, 232Th, 40K and 137Cs were determined in the soil and rice samples. The annual effective dose due to rice grain consumption in Iranians varied from 20.50±0.74 to 68.40±11.71 µSv/y. Transfer factors from soil to rice for 40K and 226Ra varied from 0.09 to 0.13 and 0.02 to 0.07, respectively. Conclusion The calculated annual effective dose due to rice grain consumption by Iranians was within the average annual global range. Therefore, this study indicated that radionuclide intake due to rice consumption had no consequence for public health. The calculated transfer factors were higher than that reported by the International Atomic Energy Agency (IAEA) in 2010; however, the values were much lower than measurements in Malaysia.

Dose Calculations for Lung Inhomogeneity in High-Energy Photon Beams and Small Beamlets: A Comparison between XiO and TiGRT Treatment Planning Systems and MCNPX Monte Carlo Code

Abstract: Introduction Radiotherapy with small fields is used widely in newly developed techniques. Additionally, dose calculation accuracy of treatment planning systems in small fields plays a crucial role in treatment outcome. In the present study, dose calculation accuracy of two commercial treatment planning systems was evaluated against Monte Carlo method. Materials and Methods Siemens Once or linear accelerator was simulated, using MCNPX Monte Carlo code, according to manufacturer’s instructions. Three analytical algorithms for dose calculation including full scatter convolution (FSC) in TiGRT, along with convolution and superposition in XiO system were evaluated for a small solid liver tumor. This solid tumor with a diameter of 1.8 cm was evaluated in a thorax phantom, and calculations were performed for different field sizes (1×1, 2×2, 3×3 and4×4 cm2). The results obtained in these treatment planning systems were compared with calculations by MC method (regarded as the most reliable method). Results For FSC and convolution algorithm, comparison with MC calculations indicated dose overestimations of up to 120%and 25% inside the lung and tumor, respectively in 1×1 cm2field size, using an 18 MV photon beam. Regarding superposition, a close agreement was seen with MC simulation in all studied field sizes. Conclusion The obtained results showed that FSC and convolution algorithm significantly overestimated doses of the lung and solid tumor; therefore, significant errors could arise in treatment plans of lung region, thus affecting the treatment outcomes. Therefore, use of MC-based methods and super position is recommended for lung treatments, using small fields and beamlets.

A Fuzzy Expert System for Distinguishing between Bacterial and Aseptic Meningitis

Abstract: Introduction Bacterial meningitis is a known infectious disease which occurs at early ages and should be promptly diagnosed and treated. Bacterial and aseptic meningitis are hard to be distinguished. Therefore, physicians should be highly informed and experienced in this area. The main aim of this study was to suggest a system for distinguishing between bacterial and aseptic meningitis, using fuzzy logic. Materials and Methods In the first step, proper attributes were selected using Weka 3.6.7 software. Six attributes were selected using Attribute Evaluator, InfoGainAttributeEval, and Ranker search method items. Then, a fuzzy inference engine was designed using MATLAB software, based on Mamdani’s fuzzy logic method with max-min composition, prod-probor, and centroid defuzzification. The rule base consisted of eight rules, based on the experience of three specialists and information extracted from textbooks. Results Data were extracted from 106 records of patients with meningitis (42 cases with bacterial meningitis) in order to evaluate the proposed system. The system accuracy, specificity, and sensitivity were 89%, 92 %, and 97%, respectively. The area under the ROC curve was 0.93, and Kappa test revealed a good level of agreement (k=0.84, P<0.0005). Conclusion According to the results, the suggested fuzzy system showed a good agreement and high efficiency in terms of distinguishing between bacterial and aseptic meningitis. To avoid unnecessary antibiotic treatments, patient hospitalization, and misdiagnosis of bacterial meningitis, such systems are useful and highly recommended. However, no system has been yet introduced with 100% correct output and further research is required to improve the results.

Design of Light Multi-layered Shields for Use in Diagnostic Radiology and Nuclear Medicine via MCNP5 Monte Carlo Code

Abstract: Introduction Lead-based shields are the most widely used attenuators in X-ray and gamma ray fields. The heavy weight, toxicity and corrosion of lead have led researchers towards the development of non-lead shields. Materials and Methods The purpose of this study was to design multi-layered shields for protection against X-rays and gamma rays in diagnostic radiology and nuclear medicine. In this study, cubic slabs composed of several materials with high atomic numbers, i.e., lead, barium, bismuth, gadolinium, tin and tungsten, were simulated, using MCNP5 Monte Carlo code. Cubic slabs (30×30×0.05 cm3) were simulated at a 50 cm distance from the point photon source. The X-ray spectra of 80 kVp and 120 kVp were obtained, using IPEM Report 78. The photon flux following the use of each shield was obtained inside cubic tally cells (1×1×0.5 cm3) at a 5 cm distance from the shields. The photon attenuation properties of multi-layered shields (i.e., two, three, four and five layers), composed of non-lead radiation materials, were also obtained via Monte Carlo simulations. Results Among different shield designs proposed in this study, the three-layered shield, composed of tungsten, bismuth and gadolinium, showed the most significant attenuation properties in radiology, with acceptable shielding at 140 keV energy in nuclear medicine. Conclusion According to the results, materials with k-edges equal to energies common to diagnostic radiology can be proper substitutes for lead shields.

Medium-Term Stability of the Photon Beam Energy of An Elekta CompactTM Linear Accelerator Based on Daily Measurements of Beam Quality Factor

Abstract: Introduction In this study, we aimed to assess the medium-term energy stability of a 6MV Elekta CompactTM linear accelerator. To the best of our knowledge, this is the first published article to evaluate this linear accelerator in terms of energy stability. As well as investigating the stability of the linear accelerator energy over a period of several weeks, the results will be useful for estimation of the required tolerance values for the beam quality factor (BQF) of the PTW QUICKCHECK weblineTM (QCW) daily checking device. Materials and Methods Over a 13 week period of routine clinical service, 52 daily readings of BQF were taken and then analyzed for a 10×10 cm2 field. Results No decreasing or increasing trend in BQF was observed over the study period. The mean BQF value was estimated at 5.4483 with a standard deviation (SD) of 0.0459 (0.8%). The mean value was only 0.1% different from the baseline value. Conclusion The results of this medium-term stability study of the Elekta Compact linear accelerator energy showed that 96.2% of the observed BQF values were within ±1.3% of the baseline value. This can be considered to be within the recommended tolerance for linear accelerator photon beam energy. If an approach of applying ±3 SD is taken, the tolerance level for BQF may be suggested to be set at ±2.5%. However, further research is required to establish a relationship between BQF value and the actual changes in beam energy and penetrative quality.

Determination of Radionuclide Concentrations in Tea Samples Cultivated in Guilan Province, Iran

Abstract: Introduction Foodstuffs are known to contain natural and artificial radionuclides. Determination of radionuclide concentration is of great significance for the protection of human health. The main objective of the present study was the quantification of radionuclides in tea samples, cultivated in Guilan Province in North of Iran. Materials and Methods The activity concentrations of 226Ra, 232Th, 40K, and 137Cs in 18 tea samples were measured, using a gamma spectrometry system. In addition, radium equivalent index (Raeq) and radiation hazard index (HI) were calculated. ANOVA test was used for the statistical analysis of the data Results The concentration of 137Cs was below the minimum detectable activity (MDA). The concentrations of 226Ra and 232Th ranged from < MDA to 0.042 and < MDA to 0.037 Bq/kg respectively. The mean concentration of 40K was 410±15 Bq/kg. Based on the findings, the concentration of 40K was significantly higher than other radionuclides (P<0.01). Also, the mean Raeq value was estimated at 31.8±1.2 Bq/kg, and HI in the samples ranged from 0.075 to 0.093. Conclusion According to the findings, the activity level of radionuclides in tea samples was found to be within the acceptable range and therefore, non-threatening to public health.

Design and Simulation of Photoneutron Source by MCNPX Monte Carlo Code for Boron Neutron Capture Therapy

Abstract: Introduction Electron linear accelerator (LINAC) can be used for neutron production in Boron Neutron Capture Therapy (BNCT). BNCT is an external radiotherapeutic method for the treatment of some cancers. In this study, Varian 2300 C/D LINAC was simulated as an electron accelerator-based photoneutron source to provide a suitable neutron flux for BNCT. Materials and Methods Photoneutron sources were simulated, using MCNPX Monte Carlo code. In this study, a 20 MeV LINAC was utilized for electron-photon reactions. After the evaluation of cross-sections and threshold energies, lead (Pb), uranium (U) and beryllium deuteride (BeD2)were selected as photoneutron sources. Results According to the simulation results, optimized photoneutron sources with a compact volume and photoneutron yields of 107, 108 and 109 (n.cm-2.s-1) were obtained for Pb, U and BeD2 composites. Also, photoneutrons increased by using enriched U (10-60%) as an electron accelerator-based photoneutron source. Conclusion Optimized photoneutron sources were obtained with compact sizes of 107, 108 and 109 (n.cm-2.s-1), respectively. These fluxs can be applied for BNCT by decelerating fast neutrons and using a suitable beam-shaping assembly, surrounding electron-photon and photoneutron sources.

Two Dimensional Mathematical Model of Tumor Angiogenesis: Coupling of Avascular Growth and Vascularization

Abstract: Introduction As a tumor grows, the demand for oxygen and nutrients increases and it grows further if acquires the ability to induce angiogenesis. In this study, we aimed to present a two-dimensional continuous mathematical model for avascular tumor growth, coupled with a discrete model of angiogenesis. Materials and Methods In the avascular growth model, tumor is considered as a single mass, which uptakes oxygen through diffusion and invades the extracellular matrix (ECM). After the tumor reaches its maximum size in the avascular growth phase, tumor cells may be in three different states (proliferative, quiescent and apoptotic), depending on oxygen availability. Quiescent cells are assumed to secrete tumor angiogenic factors, which diffuse into the surrounding tissue until reaching endothelial cells. The mathematical model for tumor angiogenesis is consisted of a five-point finite difference scheme to simulate the progression of endothelial cells in ECM and their penetration into the tumor. Results The morphology of produced networks was investigated, based on various ECM degradation patterns. The generated capillary networks involved the rules of microvascular branching and anastomosis. Model predictions were in qualitative agreement with experimental observations and might have implications as a supplementary model to facilitate mathematical analyses for anti-cancer therapies. Conclusion Our numerical simulations could facilitate the qualitative comparison between three layers of tumor cells, their TAF-producing abilities and subsequent penetration of micro-vessels in order to determine the dynamics of microvascular branching and anastomosis in ECM and three different parts of the tumor.

Improvement of Breast Cancer Detection Using Non-subsampled Contourlet Transform and Super-Resolution Technique in Mammographic Images

Abstract: Introduction Breast cancer is one of the most life-threatening conditions among women. Early detection of this disease is the only way to reduce the associated mortality rate. Mammography is a standard method for the early detection of breast cancer. Today, considering the importance of breast cancer detection, computer-aided detection techniques have been employed to increase the quality of mammographic images and help physicians reduce false positive rate (FPR). Materials and Methods In this study, a method was proposed for improving the quality of mammographic images to help radiologists establish a prompt and accurate diagnosis. The proposed approach included three major parts including pre-processing, feature extraction, and classification. In the pre-processing stage, the region of interest was determined and the image quality was improved by non-subsampled contourlet transform and super-resolution algorithm. In the feature extraction stage, some features of image components were extracted and skewness of each feature was calculated. Finally, a support vector machine was utilized to classify the features and determine the probability of benignity or malignancy of the disease. Results Based on the obtained results using Mammographic Image Analysis Society (MIAS) database, the mean accuracy was estimated at 87.26% and maximum accuracy was 96.29%. Also, the mean and minimum FPRs were estimated at 9.55% and 2.87%, respectively. Conclusion The results obtained using MIAS database indicated the superiority of the proposed method to other techniques. The reduced FPR in the proposed method was a significant finding in the present article.

Material-specific Conversion Factors for Different Solid Phantoms Used in the Dosimetry of Different Brachytherapy Sources

Abstract: Introduction Based on Task Group No. 43 (TG-43U1) recommendations, water phantom is proposed as a reference phantom for the dosimetry of brachytherapy sources. The experimental determination of TG-43 parameters is usually performed in water-equivalent solid phantoms. The purpose of this study was to determine the conversion factors for equalizing solid phantoms to water. Materials and Methods TG-43 parameters of low- and high-energy brachytherapy sources (i.e., Pd-103, I-125 and Cs-137) were obtained in different phantoms, using Monte Carlo simulations. The brachytherapy sources were simulated at the center of different phantoms including water, solid water, poly(methyl methacrylate), polystyrene and polyethylene. Dosimetric parameters such as dose rate constant, radial dose function and anisotropy function of each source were compared in different phantoms. Then, conversion factors were obtained to make phantom parameters equivalent to those of water. Results Polynomial coefficients of conversion factors were obtained for all sources to quantitatively compare g(r) values in different phantom materials and the radial dose function in water. Conclusion Polynomial coefficients of conversion factors were obtained for all sources to quantitatively compare g(r) values in different phantom materials and the radial dose function in water.

A Novel Spot-Enhancement Anisotropic Diffusion Method for the Improvement of Segmentation in Two-dimensional Gel Electrophoresis Images, Based on the Watershed Transform Algorithm

Abstract: Introduction Two-dimensional gel electrophoresis (2DGE) is a powerful technique in proteomics for protein separation. In this technique, spot segmentation is an essential stage, which can be challenging due to problems such as overlapping spots, streaks, artifacts and noise. Watershed transform is one of the common methods for image segmentation. Nevertheless, in 2DGE image segmentation, the noise and artifacts of images cause over-segmentation in the watershed algorithm. Materials and Methods In this study, we proposed a novel spot-enhancement anisotropic diffusion (SEAD) method, based on multi-scale second-order derivatives and eigensystemto enhance the spots and remove noise and artifacts. The proposed SEAD algorithm was plugged to a watershed transform in order to improve the performance of watershed segmentation algorithm. Results The performance of the proposed SEAD method was evaluated on synthetic and real 2DGE images. The proposed algorithm was compared with other segmentation methodsin terms of different criteria including efficiency, precision and true positive rate. The performance of the methods were evaluated in the presence of noise and the results were evaluated by t-test. According to the count of detected spots, precision and efficiency of the proposed method were 0.82 and 0.67 respectively. The precision and efficiency values of the comparative methods were as follows: 0.65 and 0.42 for MCW algorithm, 0.40 and 0.37 for BWT method, 0.74 and 0.53 for the method proposed by Kostopoulou and 0.76 and 0.55 for the method proposed by Mylona. Conclusion The comparison of the proposed method with four other conventional methods revealed the superiority and effectiveness of the proposed SEAD method.

Assessment of Effective Dose Equivalent from Internal Exposure to 222Rn in Ramsar City

Abstract: Introduction In this study, effective dose equivalent for the public due to internal exposure to 222radon (222Rn) was evaluated in three regions of Ramsar, a northern coastal city in Iran. Materials and Methods Measurements were carried out using a radon monitoring device. Outdoor and indoor radon concentrations were measured within 24 hours with an integration interval of 3 hours. Regions were selected with respect to our previous study on areas of Ramsar with high levels of environmental background radiation. Results This study showed that indoor 222Rn concentration reached to 465 Bq/m3 in one of the selected regions (Talesh Mahalleh) in early morning (5-8 a.m.). Our study also showed that the average effective dose equivalents (due to both indoor and outdoor exposures) in the selected regions (Talesh Mahalleh, Sadat Mahalleh, and Chaparsar) were 9.5±2.8, 5.1±2.1, and 3.2±1.2 mSv/y, respectively. Conclusion It is clear that the annual effective dose from internal exposure to 222Rn in areas of Ramsar with high levels of natural radiation was significantly higher than the maximum annual effective dose permissible for public.

Step-and-Shoot versus Compensator-based IMRT: Calculation and Comparison of Integral Dose in Non-tumoral and Target Organs in Prostate Cancer

Abstract: Introduction Intensity-Modulated Radiotherapy (IMRT) is becoming an increasingly routine treatment method. IMRT can be delivered by use of conventional Multileaf Collimators (MLCs) and/or physical compensators. One of the most important factors in selecting an appropriate IMRT technique is integral dose. Integral dose is equal to the mean energy deposited in the total irradiated volume of the patient. The aim of the present study was to calculate and compare the integral dose in normal and target organs in two different procedures of IMRT: Step-and-Shoot (SAS) and compensator-based IMRT. Materials and Methods In this comparative study, five patients with prostate cancer were selected. Module Integrated Radiotherapy System was applied, using three energy ranges. In both treatment planning methods, the integral dose dramatically decreased by increasing energy. Results Comparison of two treatment methods showed that on average, the integral dose of body in SAS radiation therapy was about 1.62% lower than that reported in compensator-based IMRT. In planning target volume, rectum, bladder, and left and right femoral heads, the integral doses for SAS method were 1.01%, 1.02%, 1.11%, 1.47%, and 1.40% lower than compensator-based IMRT, respectively. Conclusion Considering the treatment conditions, the definition of dose volume constraints for healthy tissues, and the equal volume of organs in both treatment methods, SAS radiation therapy by providing a lower integral dose seems to be more advantageous and efficient for prostate cancer treatment, compared to compensator-based IMRT.

Calculation of the Dose of Samarium-153-Ethylene Diamine Tetramethylene Phosphonate (153Sm-EDTMP) as a Radiopharmaceutical for Pain Relief of bone Metastasis

Abstract: Introduction One of the important applications of nuclear physics in medicine is the use of radioactive elements as radiopharmaceuticals. Metastatic bone disease is the most common form of malignant bone tumors. Samarium-153-ethylene diamine tetramethylene phosphonate (153Sm-EDTMP) as a radiopharmaceutical is used for pain palliation. This radiopharmaceutical usually emits beta particles, which have a high uptake in bone tissues. The purpose of this study was to calculate the radiation dose distribution of 153Sm-EDTMP in bone and other tissues, using MCNPX Monte Carlo code in the particle transport model. Materials and Methods Dose delivery to the bone was simulated by seeking radiopharmaceuticals on the bone surface. The phantom model had a simple cylindrical geometry and included bone, bone marrow, and soft tissue. Results The simulation results showed that a significant amount of radiation dose was delivered to the bone by the use of this radiopharmaceutical. Conclusion Thebone acted as a fine protective shield against rays for the bone marrow. Therefore, the trivial absorbed dose by the bone marrow caused less damage to bone-making cells. Also, the high absorbed dose of the bone could destroy cancer cells and relieve the pain in the bone.

Experimental Evaluation of Depth Dose by Exit Surface Diode Dosimeters for Off-Axis Wedged Fields in Radiation Therapy

Abstract: Introduction Evaluation of the delivered dose of externally wedged photon beams by external diode dosimeters during the treatment process requires the estimation of exit surface dose correction factors in various wedge angles and field sizes. Materials and Methods A system of absorbed dose evaluation, using p-type diode dosimeters placed on the exit surface of a phantom, was characterized for externally wedged photons with the maximum square field size. The values of wedge correction factor on the exit surface of the polystyrene phantom were determined for 60Co and 6 MV photons. Then, the wedge correction factors were estimated at desirable depths. Results Based on the findings, the deviation of off-axis wedge correction factors of the exit surface wedged fields from the central axis factor may be as large as ±10% at the evaluated depths. The results showed that the absorbed dose at each depth of patient tissue could be estimated by applying an accurate exit wedge correction factor for that particular depth, with negligible probable errors (below 1.5%). Conclusion In case positioning a diode dosimeter on the patient’s entrance surface of a phantom of patients is troublesome, the diode dosimeter can be placed on the exit surface in order to evaluate the absorbed dose for externally wedged photons. Based on the findings, exit dose correction factors for wedged beams cannot be discarded; in fact, these factors are variable at different directions of externally wedged beams.

Induction of Localized Hyperthermia by Millisecond Laser Pulses in the Presence of Gold-Gold Sulphide Nanoparticles in a Phantom

Abstract: Introduction Application of near-infrared absorbing nanostructures can induce hyperthermia, in addition to providing more efficient photothermal effects. Gold-gold sulfide (GGS) is considered as one of these nanostructures. This study was performed on a tissue-equivalent optical-thermal phantom to determine the temperature profile in the presence and absence of GGS and millisecond pulses of a near-infrared laser. Moreover, the feasibility of hyperthermia induction was investigated in a simulated tumor. Materials and Methods A tumor with its surrounding tissues was simulated in a phantom made of Agarose and Intralipid. The tumor was irradiated by 30 laser pulses with durations of 30, 100, and 400 ms and fluences of 40 and 60 J/cm2. Temperature variations in the phantom with and without GGS were recorded, using fast-response sensors of a digital thermometer, placed at different distances from the central axis at three depths. The temperature rise was recorded by varying duration and fluence of the laser pulses. Results The rise in temperature was recorded by increasing laser fluence and number of pulses for three durations. The temperature profile was obtained at each depth. The presence of GGS resulted in a significant increase in temperature in all cases (P<0.035). Also, the laser temperature had a slower reduction in the presence of GGS, compared to its absence after turning the laser off (P<0.001). Conclusion The millisecond laser pulses could induce hyperthermia in a relatively large target tissue volume. GGS as a simple and cost-effective synthesized nanostructure could induce localized hyperthermia in the desired region during near-infrared laser irradiation.

Assessment of the Preventive Effect of Pilocarpine on Radiotherapy-Induced Xerostomia in Patients with Head and Neck Cancers

Abstract: Introduction Xerostomia is one of side-effects of radiotherapy for head and neck cancers. No definitive method has been proposed for the treatment of this condition. However, pilocarpine is considered effective for the management of chronic xerostomia. The purpose of the present study was to assess the preventive effect of pilocarpine. Materials and Methods This study was performed on 34 patients with head and neck cancers, undergoing radiation therapy (5000 cGy). The patients were randomly divided into two groups. The case group was administered 16 drops of pilocarpine (2%) eye drops per day, while the control group received normal saline; the treatment plan continued for four weeks. Unstimulated whole saliva flow rate was measured at four stages: two weeks before radiotherapy (baseline), the first day of radiotherapy, and two and four weeks after the initiation of radiotherapy. Results At baseline and the first day of radiotherapy, no significant differences were observed in the amount of saliva between the case and control groups (PConclusion According to the findings, pilocarpine was found to be effective for the prevention of xerostomia. Moreover, it could restrain the decline in the amount of saliva and reduce the rate of xerostomia.

Different Aspects of Ultra-weak Photon Emissions: A Review Article

Abstract: All biological samples emit ultra-low intensity light without any external stimulation. Recently, scientific communities have paid particular attention to this phenomenon, known as ultra-weak photon emission (UPE). UPE has been introduced in the literature as an alternative for biophoton, low-level chemiluminescence and ultra-weak bioluminescence, while it differs from ordinary bioluminescence, fluorescence and phosphorescence. Some UPE parameters including spectrum and intensity have been already recognized, while other features such as the main origin(s), statistical distribution and fractality of UPE are partially understood. Ultra-weak photon detection has a broad range of potential applications in different industries such as agriculture and medicine. The correlation between UPE and physiological state of a system facilitates the use of UPE as a completely non-invasive diagnostic method in cases such as cancer detection. In this review article, we aimed to provide useful information on specific characteristics, possible origin(s) and potential applications of UPE. Moreover, we introduced some physical models for UPE and presented several controversial hypotheses in this context.

A Survey on the Possibility of Utilizing gamma H2AX as a Biodosimeter in Radiation Workers

Abstract: Introduction DNA damage is among the main consequences of radiation. Of many different classes of DNA damage, double-strand breaks are the most deleterious. Development of a sensitive biodosimetry method, which utilizes a detection material with a similar construction to the body, seems essential for monitoring radiation workers. In this study, histone H2AX protein was examined as a potential biodosimeter in radiation workers. Moreover, the presence of this protein after in vitro irradiation of blood samples was assessed simultaneously. Materials and Methods Blood samples from 46 radiation workers were analyzed in Golestan province, Iran. Meanwhile, two groups of blood samples (five blood samples in each group) were irradiated in vitro by doses of 1 to 0.2 Gy and 0.09 to 0.01 Gy from a 60Co source, respectively. gH2AX level in lymphocytes was measured, using Western blot technique. ANOVA and Tukey’s tests were performed, using SPSS version 16. The significance level was considered to be 0.05. Results The results of Western blotting for the identification of gH2AX protein in radiation workers were negative. However, gH2AX level in lymphocytes of two in vitro irradiated groups showed a significant correlation with the radiation dose (P<0.0001). Conclusion The results showed that gH2AX was a good indicator for acute or local exposure to ionizing radiation, while in chronically exposed individuals, including radiation workers, this protein was useless at least in autoradiography detection method. Regarding the presence of gH2AX protein in blood samples, which were irradiated in vitro at low doses, it can be concluded that this protein has powerful repair mechanisms.

Dose Measurements of Parotid Glands and Spinal Cord in Conventional Treatment of Nasopharyngeal Carcinoma Using RANDO Phantom and Thermoluminescent Dosimeters

Abstract: Introduction Radiotherapy is regarded as the first treatment of choice for nasopharyngeal carcinoma. Despite the advantages of radiotherapy, patients may suffer from a wide range of side-effects due to the presence of many sensitive normal tissues in these regions. If the absorbed dose exceeds the tolerance level in parotid glands and the spinal cord, myelopathy, Lhermitte's sign and xerostomia cannot be avoided. Materials and Methods The head and neck of a RANDO phantom (reference man), which was regarded as a hypothetical patient with nasopharyngeal carcinoma was evaluated. The full course of treatment consisted of three phases. At the beginning of each phase, an oncologist marked conventional fields on the RANDO phantom using a simulator. For measuring the absorbed dose, Thermoluminescent Dosimeters(TLD) chips (TLD-100) were utilized.The absorbed dose by TLDs was read by Harshaw 3500 TLD reader. Results The total absorbed dose was calculated by measuring the absorbed dose in each phase, multiplied by the fraction numbers of each phase; the obtained values were summed up. The results showed that the received doses by spinal cord ranged from 15.24 to 54.56 Gy. Also, the absorbed dose of parotid glands was approximately 39.23 Gy. Conclusion Considering the minimum tolerance dose the absorbed doses in the spinal cord and parotid glands were above the tolerance level. The incidence rate of xerostomia and myelopathy were higher in patients, treated by conventional methods.

A Hybrid Neural Network Approach for Kinematic Modeling of a Novel 6-UPS Parallel Human-Like Mastication Robot

Abstract: Introduction we aimed to introduce a 6-universal-prismatic-spherical (UPS) parallel mechanism for the human jaw motion and theoretically evaluate its kinematic problem. We proposed a strategy to provide a fast and accurate solution to the kinematic problem. The proposed strategy could accelerate the process of solution-finding for the direct kinematic problem by reducing the number of required iterations in order to reach the desired accuracy level. Materials and Methods To overcome the direct kinematic problem, an artificial neural network and third-order Newton-Raphson algorithm were combined to provide an improved hybrid method. In this method, approximate solution was presented for the direct kinematic problem by the neural network. This solution could be considered as the initial guess for the third-order Newton-Raphson algorithm to provide an answer with the desired level of accuracy. Results The results showed that the proposed combination could help find a approximate solution and reduce the execution time for the direct kinematic problem, The results showed that muscular actuations showed periodic behaviors, and the maximum length variation of temporalis muscle was larger than that of masseter and pterygoid muscles. By reducing the processing time for solving the direct kinematic problem, more time could be devoted to control calculations.. In this method, for relatively high levels of accuracy, the number of iterations and computational time decreased by 90% and 34%, respectively, compared to the conventional Newton method. Conclusion The present analysis could allow researchers to characterize and study the mastication process by specifying different chewing patterns (e.g., muscle displacements).

Assessment of Patients’ Entrance Skin Dose from Diagnostic X-ray Examinations at Public Hospitals of Akwa Ibom State, Nigeria

Abstract: Introduction High doses of ionizing radiation can lead to adverse health outcomes such as cancer induction in humans. Although the consequences are less evident at very low radiation doses, the associated risks are of societal importance. This study aimed at assessing entrance skin doses (ESDs) in patients undergoing selected diagnostic X-ray examinations at public hospitals of Akwa Ibom State, Nigeria. Materials and Methods In total, six examinations were performed on 720 patients in this study. CALDose_X5 software program was used in estimating ESDs based on patients’ information and technical exposure parameters. Results The estimated ESDs ranged from 0.59 to 0.61 mGy for PA and RLAT projections of the thorax, respectively. ESDs for the AP and RLAT projections of the cranium were 1.65 and 1.48 mGy, respectively. Also, ESD values for the AP view of the abdomen and pelvis were 1.89 and 1.88 mGy, respectively. The mean effective dose was within the range of 0.021-0.075 mGy for the thorax (mean= 0.037), 0.008-0.045 mGy for the cranium (mean= 0.016), 0.215-0.225 mGy for the abdomen (mean= 0.219) and 0.101-0.119 mGy for the pelvis (mean= 0.112). Conclusion The obtained results were comparable to the international reference dose levels, except for the PA projection of the thorax. Therefore, quality assurance programs are required in diagnostic X-ray units of Nigeria hospitals. The obtained findings add to the available data and can help authorities establish reference dose levels for diagnostic radiography in Nigeria.

Calculation of Positron Distribution in the Presence of a Uniform Magnetic Field for the Improvement of Positron Emission Tomography (PET) Imaging Using GEANT4 Toolkit

Abstract: Introduction Range and diffusion of positron-emitting radiopharmaceuticals are important parameters for image resolution in positron emission tomography (PET). In this study, GEANT4 toolkit was applied to study positron diffusion in soft tissues with and without a magnetic field for six commonly used isotopes in PET imaging including 11C, 13N, 15O, 18F, 68Ga, and 82Rb. Materials and Methods GEANT4 toolkit was used to simulate the transport and interactions of positrons. Calculations were performed for the soft tissue phantom (8 mm ×8 mm × 8 mm). Positrons were emitted isotropically from the center of the phantom. By the application of a magnetic field perpendicular to the path of positrons, lateral scattering of positrons could be prevented due to Lorentz force. When the positron energy was below the cut-off threshold (0.001 MeV), the simulation was terminated. Results The findings showed that the presence of a magnetic field increased the rate of positron annihilation. At magnetic field strengths of 3, 7, and 10 Tesla, 18F with the lowest decay energy showed improvements in the ratio of full width at half maximum (FWHM) resolution to the peak of curve by 3.64%, 3.89%, and 5.96%, respectively. In addition, at magnetic field strengths of 3, 7 and 10 Tesla, 82Rb with the highest decay energy showed improvements in resolution by 33%, 85%, and 99%, respectively. Conclusion Application of a magnetic field perpendicular to the positron diffusion plane prevented the scattering of positrons, and consequently, improved the intrinsic spatial resolution of PET imaging, caused by positron range effects.

Evaluation of Personal Shields Used in Selected Radiology Departments

Abstract: Introduction The purpose of this study was to evaluate personal shields in radiation departments of hospitals affiliated to Mashhad University of Medical Sciences. Materials and Methods First, the information related to 109 personal shields was recorded and evaluated by imaging equipment. Afterwards, the equivalent lead thickness (ELT) of 62 personal shields was assessed, using dosimeter and standard lead layers at 100 kVp. Results In this study, 109 personal shields were assessed in terms of tears, holes and cracks. The results showed that 18 shields were damaged. Moreover, ELT was evaluated in 62 shields. As the results indicated, ELT was unacceptable in 8 personal shields and lower than expected in 9 shields. Conclusion According to the results, 16.5% of personal shields had defects (tears, holes and cracks) and 13% of them were unacceptable in terms of ELT and needed to be replaced. Therefore, regular quality control of personal shields and evaluation of new shields are necessary at any radiation department.

Preliminary Dosimetry Study of 67Ga-AATS for Human Based on Biodistribution Data in Rats

Abstract: Introduction Gallium-67 (67Ga) has been used as a radionuclide for imaging a variety of solid tumors since 1969. Since then use of various gallium-based radiotracers has been reported. Recently, 67Ga-labeled acetylacetate bis(thiosemicarbazones) (67Ga-AATS) complex with significant tumor accumulation and fast blood clearance has been employed. Materials and Methods In this study, the absorbed dose of 67Ga-AATS in each human organ was evaluated and compared with 67Ga-citrate as the most commonly used form of 67Ga in nuclear medicine. 67Ga was produced via 68Zn(p,2n)67Ga reaction at 30 MeV cyclotron. Moreover, 67Ga-AATS was produced by adding 50 µl of AATS to absolute ethanol (1 mg/ml) in a gallium-containing vial at 80-90 °C. The absorbed dose of each human organ was calculated, using RADAR method, based on biodistribution data in Wistar rats. Results According to the results, 67Ga-AATS was produced with radionuclidic and radiochemical purity higher than 99% and 93%, respectively. The highest absorbed dose was reported in the bone surface (0.401 mGy/MBq), whereas the whole-body absorbed dose was 0.092 mGy/MBq. Conclusion The absorbed dose of each human organ was comparable with the absorbed dose received by each organ after 67Ga-citrate injection. Considering this interesting finding and the significant tumor uptake, it seems that 67Ga-AATS can be used as an appropriate SPECT tracer.

Secondary Particles Produced by Hadron Therapy

Abstract: Introduction Use of hadron therapy as an advanced radiotherapy technique is increasing. In this method, secondary particles are produced through primary beam interactions with the beam-transport system and the patient’s body. In this study, Monte Carlo simulations were employed to determine the dose of produced secondary particles, particularly neutrons during treatment. Materials and Methods In this study, secondary particles, produced by proton and ion beams, were simulated for a cancer treatment plan. In particular, we evaluated the distribution of secondary neutrons, produced by a 400 MeV/u carbon beam on an electronic crate, which was exposed to radiation field under radioactive conditions. The level of major secondary particles, particularly neutrons, irradiating the target, was evaluated, using FLUKA Monte Carlo code. Results The fluences and radiation doses were applied to determine the shielding efficiency of devices and the probability of radiation damage to nearby electronic systems. According to the results, by using maximum-energy carbon ions (400 MeV/u), electronic devices are exposed to a dose rate of 0.05 µSv/s and an integrated dose of about 34 mSv, each year. Conclusion The simulation results could provide significant information about radiation assessment; they could also be a major help for clinical facilities to meet shielding requirements. Moreover, such simulations are essential for determining the radiation level, which is responsible for radiation-induced damages.