Journal of Biomedical Physics & Engineering
Volume:9 Issue: 2, Mar-Apr 2019

This study investigates basic dosimetric properties of unflattened 6 MV photon beam shaped by multileaf collimator and compares them with those of flattened beams. Monte Carlo simulation model using BEAM code was developed for a 6MV photon beam based on Varian Clinic 600 unique performance linac operated with and without a flattening filter in beam line. Dosimetric features including lateral profiles, central axis depth dose, photon and electron spectra were calculated for flattened and unflattened cases, separately. An increase in absolute depth dose with a factor of more than 2.4 was observed for unflattened beam which was dependent on depth. PDDs values were found to be lower for unflattened beam for all field sizes. Significant decrease in calculated mlc leakage was observed when the flattening filter was removed from the beam line. The total scatter factor, SCP was found to show less variation with field sizes for unflattened beam indicating a decrease in head scatter. The beam profiles for unflattened case are found to have lower relative dose value in comparison with flattened beam near the field edge, and it falls off faster with distance. Our study showed that increase in the dose rate and lower peripheral dose could be considered as realistic advantages for unflattened 6MV photon beams.

Craniospinal irradiation (CSI) of medulloblastoma poses technological challenges due to the involvement of large treatment volume. Commonly, the whole treatment length is covered with two different isocentric plans in which the junction is shifted after every five fractions to overcome the possibility of hot and cold spot. This study aims to evaluate dosimetrically and clinically the innovative planning technique for the CSI which doesn’t need re-planning and re-setup of patients after every five fractions. Computed tomography was done for fifteen (ten children and five adults) patients diagnosed with medulloblastoma. Treatment planning for 36 Gray (Gy) in 20 fractions (#) at the rate of 1.8Gy/# was done on the treatment planning system. A single plan for children was created with two bilateral fields of 6 Mega Voltage (MV) energy for cranium and one posterior field of 6 MV for spinal cord (C1-S2). Two plans for adult patients were created, first plan was with two bilateral fields of 6 MV for cranium and two posterior oblique fields of 6 MV for cervical and the part of thoracic spinal cord (up to T8-T9). The second plan was with a single posterior field of 15 MV covering remaining thoracic (T8-T9 to T12), lumbar and sacrum (up to lower border of S2) spine. After careful evaluation of all the plans, treatment was delivered; acute toxicities were recorded. 95% of prescribed dose was received by more than 95% of planning target volume in all the plans with the acceptable hot spot and good homogeneity index. All the patients reported common radiation induced acute toxicities (headache, vomiting, weakness) during radiotherapy. The new planning technique for CSI has acceptable dosimetric and acute clinical possibilities; therefore it can be used for CSI for improved homogeneous dose delivery.

For preclinical evaluations of radiopharmaceuticals, most studies are carried out on mice. Values of electron specific absorbed fractions (SAF) have had vital role in the assessment of absorbed dose. In past studies, electron specific absorbed fractions were given for limited source target pairs using older reports of human organ compositions. Electron specific absorbed fraction values for monoenergetic electrons of energies 15, 50, 100, 500, 1000 and 4000 keV were evaluated for the Digimouse voxel phantom incorporated in Monte Carlo code FLUKA. The organ sources considered in this study were lungs, skeleton, heart, bladder, testis, stomach, spleen, pancreas, liver, kidney, adrenal, eye and brain. The considered target organs were lungs, skeleton, heart, bladder, testis, stomach, spleen, pancreas, liver, kidney, adrenal and brain. Eye and brain were considered as target organs only for eye and brain as source organs. From the latest report (International Commission on Radiological Protection ICRP) publication number 110, organ compositions and densities were adopted. The electron specific absorbed fraction values for self-irradiation decreases with increasing electron energy. The electron specific absorbed fraction values for cross-irradiation are also found to be dependent on the electron energy and the geometries of source and target. Organ masses and electron specific absorbed fraction values are presented in tabular form.  The results of this study will be useful in evaluating the absorbed dose to various organs of mice similar in size to the present study.

 Carious lesions are formed by a complex process of chemical interaction between dental enamel and its environment. They can cause cavities and pain, and are expensive to fix. It is hard to characterize in vivo as a result of environment factors and remineralization by ions in the oral cavity.  The development of a technique that gives early diagnosis which is non-invasive, is of crucial importance for publichealth. Raman spectroscopy is a technique that can fulfil these requirements. The main goal of this work was to use Raman spectroscopy to differentiate between normal and carious human teethinvivo. The samples used in this study were collected by traditional human teeth.  An in vivo Raman spectroscopy system andspecialized fiber optic probe has been designed to obtain spectra from tissue. Theseprobes are filtered to reduce the background signal from the fiber optics and the collection fiberutilizes beam steering to optimize the collection effectiv.  In order to detect any demineralization and carious versus sound pit and fissure enamel, the spectral data sets are analyzed by the proposed scheme to demonstrate the utility of generalized 2D correlation spectra. Potential applications of this 2D correlation approach are then explored. The Raman spectra in the normal tissue showed thepresence of vibrational bands in 437.87 cm-1, 581.89 cm-1, 953.89 cm-1 and 1054.73 cm-1 with smaller intensity than in the carious spectra. Image construction from the peak intensity produced chemical maps of apatite concentration. Such two-dimensional correlation spectra emphasize spectral features not readily observable in conventional one-dimensional spectra.No correlation is observed in mode-to-mode intensity fluctuations indicating that the changes inmode intensities are completely independent. Theoreticalcalculations provide convincing evidence that the fluctuationsare not the result of diffusion, orientation or local electromagnetic field gradients but rather are the result of subtle variations ofthe excited-state lifetime, energy and geometry of the molecule and producing a signature response for carious detection.

Given the importance of scattered and low doses in secondary cancer caused by radiation treatment, the point dose of critical organs, which were not subjected to radiation treatment in breast cancer radiotherapy, was measured. The purpose of this study is to evaluate the peripheral dose in two techniques of breast cancer radiotherapy with two energies.  Eight different plans in two techniques (conventional and conformal) and two photon energies (6 and 15 MeV) were applied to Rando Alderson Phantom’s DICOM images. Nine organs were contoured in the treatment planning system and specified on the phantom. To measure the photon dose, forty-eight thermoluminescence dosimeters (MTS700) were positioned in special places on the above nine organs and plans were applied to Rando phantom with Elekta presice linac. To obtain approximately the same dose distribution in the clinical organ volume, a wedge was used on planes with an energy of 6 MeV photon.          Point doses in critical organs with 8 different plans demonstrated that scattering in low-energy photon is greater than high-energy photon. In contrast, neutron contamination in high-energy photon is not negligible. Using the wedge and shield impose greater scattering and neutron contamination on patients with low-and high-energy photon, respectively.     Deciding on techniques and energies required for preparing an acceptable treatment plan in terms of scattering and neutron contamination is a key issue that may affect the probability of secondary cancer in a patient.

One of the leading causes of death is brain tumors. Accurate tumor classification leads to appropriate decision making and providing the most efficient treatment to the patients. This study aims to optimize brain tumor MR images classification accuracy using optimal threshold, PCA and training Adaptive Neuro Fuzzy Inference System (ANFIS) with different repetitions. The procedure used in this study consists of five steps: (1) T1, T2 weighted images collection, (2) tumor separation with different threshold levels, (3) feature extraction, (4) presence and absence of feature reduction applying principal component analysis (PCA) and (5) ANFIS classification with 0, 20 and 200 training repetitions. ANFIS accuracy was 40%, 80% and 97% for all features and 97%, 98.5% and 100% for the 6 selected features by PCA in 0, 20 and 200 training repetitions, respectively. The findings of the present study demonstrated that accuracy can be raised up to 100% by using an optimized threshold method, PCA and increasing training repetitions.

Numerous unique characteristics of the nanosized gold, including high atomic number, low toxicity, and high biocompatibility make it one of the most appropriate nanostructures to boost radiotherapy efficacy. Many in-vivo and in-vitro investigations have indicated that gold nanoparticles (AuNPs) can significantly increase tumor injuries in low kilovoltage radiotherapy. While deep-lying tumors require much higher energy levels with greater penetration power, and investigations carried out in megavoltage energy range show contradictory results. In this study, we quantitatively assess and compare dose enhancement factors (DEFs) obtained through AuNPs under radiation of Cobalt-60 source (1.25MeV) versus Iridium-192 source (0.380 KeV) using MAGAT gel dosimeter. MAGAT polymer gel in both pure and combined with 0.2 mM AuNPs was synthesized. In order to quantify the effect of energy on DEF, irradiation was carried out by Co-60 external radiotherapy and Ir-192 internal radiotherapy. Finally, readings of irradiated and non-irradiated gels were performed by MR imaging. The radiation-induced R2 (1/T2) changes of the gel tubes doped with AuNPs compared to control samples, upon irradiation of beams released by Ir-192 source showed a significant dose enhancement (15.31% ±0.30) relative to the Co-60 external radiotherapy (5.85% ±0.14). This preliminary study suggests the feasibility of using AuNPs in radiation therapy (RT), especially in low-energy sources of brachytherapy. In addition, MAGAT polymer gel, as a powerful dosimeter, could be used for 3D visualization of radiation dose distribution of AuNPs in radiotherapy.

Magnetic resonance imaging (MRI) contrast agents have an important role to differentiate healthy and diseased tissues. Access and design new contrast agents for the optimal use of MRI are necessary. This study aims to evaluate iron oxide–4A nanocomposite ability to act as a magnetic resonance imaging contrast agent. Iron oxide–4A nanocomposite (F4A) was synthesized. MTT assay was used to consider the nanocomposite safety for cell culture. The T1 and T2 relaxation times were measured using a 1.5 Tesla clinical MRI scanner. Then the corresponding relaxivities were determined. The average particle diameter of the nanocomposite was 50 to 100 nm based on scanning electron microscope (SEM) image. A linear relationship between relaxation rates and the Fe concentration of the nanocomposite was obtained. The T1 and T2 relaxivities of the nanocomposite were calculated 5.413 and 1092.1 mM-1.s-1, respectively which led to the T2/T1 relaxivity ratioof 201.75. The high T2/T1 relaxivity ratio of the iron oxide–4A nanocomposite confirms it’s potential to act as a T2 contrast agent.

The current study investigated the combination of high Z atoms (iodine-, platinium-based drugs) with using low energy irradiation (120kvp) in Anaplastic Thyroid cancer cells. For this purpose, eight groups were designed: control (CNT), different concentrations of Iodine contrast media (ICM),  irradiation with various doses, Cis-platin (CDDP) with different concentrations, (ICM + CDDP), (ICM + RAD), (CDDP + RAD) and (ICM + CDDP + RAD). The viability was measured by MTT and Colony assay. In MTT assay, the viability of 8305c cells RAD (2 Gy)+ICM (10mg/mL) group was significantly lower than those treated with RAD or ICM alone. CDDP +ICM+RAD group significantly decreased the viability. In colony assay, cells in ICM + RAD (2 Gy) group reduced the number of colonies more significant than RAD group. The difference of colony forming ability between CDDP and CDDP + RAD (2 Gy) was significant. The difference of ICM + CDDP + RAD (2 Gy) and CDDP +RAD (2Gy) group was significant. All data were statistically analysed using one-way analysis of variance (ANOVA) followed by Chafe’s multi-comparisons tests. All data were presented as mean ± standard deviation (SD) and analysed using statistical package for social sciences (SPSS 16). Significance was considered to be p<0.05. In MTT assay, the viability of 8305c cells RAD (2 Gy) + ICM (10mg/mL) group was significantly lower than those treated with RAD or ICM alone. CDDP + ICM + RAD group significantly decreased the viability. In colony assay, cells in ICM + RAD (2 Gy) group reduced the number of colonies more significantly than RAD group. The difference of colony forming ability between CDDP and CDDP + RAD (2 Gy) was significant. The difference of ICM + CDDP + RAD (2 Gy) and CDDP + RAD (2 Gy) group was significant. Exposure of ATC to ICM in the presence of CDDP increases tissue X-rays absorbance by Auger electrons and photo electrons leading to more fatal effects against the tumour

Previous studies have shown that exposure to electromagnetic fields produced by magnetic resonance imaging or mobile phones can lead to increased microleakage of dental amalgam. The aim of the present study was to investigate the effect of electromagnetic field of a commercial dental light cure device and a common GSM mobile phone on microleakage of amalgam restorations. Identical class V cavities were prepared on the buccal surfaces of 60 non-carious extracted human teeth. The samples were randomly divided into 4 groups of 20 samples each. The samples in the first group were not exposed to electromagnetic fields, while the second and the third groups were exposed to electromagnetic fields produced by a commercial light cure device, or mobile phone radiation (60 min), respectively. The fourth group was exposed to electromagnetic radiations emitted by both mobile phone for 60 min and light cure device. Then, teeth samples were scored for microleakage according to a standard dye penetration protocol by examination under a stereomicroscope. The mean score of microleakage in the fourth group (light cure + mobile phone) was significantly higher than that of the control group (P =0.030). Moreover, the scores of microleakage in this group were significantly higher than that of the second group (light cure only) (P= 0.043). Exposure of amalgam restorations to electromagnetic fields produced by both light cure devices and mobile phones can synergistically increase the microleakage of amalgam restorations.

The maintenance of postural control is a key component in dynamic physical activity, especially during muscle fatigue and against external forces. Despite many studies in this field, there is no consensus regarding the effects of plantar flexor muscles fatigue on postural control during different postural tasks. To evaluate the effects of plantar flexor muscles fatigue on postural control during quiet stance and external perturbation in healthy subjects. Twenty four healthy individuals (20-35 years) participated this interventional study. The foot center of pressure data was measured using a single force platform, and then the postural control parameters, including the center of pressure displacement and velocity in the anterior-posterior and medial-lateral direction and also path length calculated under two conditions; quiet and perturbed stance, before and after plantar flexor muscles fatigue. The statistical analysis demonstrated that mean displacement and velocity of the center of pressure in the anterior-posterior direction and also path length increased after the fatigue protocol in the perturbed condition. However, fatigue had no significant effects on postural control parameters in the quiet standing condition. These results indicated that the effects of muscle fatigue on postural control depend on the difficulty of the task and the relevance of proprioceptive information. The postural control system appears to use distinct control strategies in different situations such as quiet and perturbed stance conditions, and these strategies may be differentially altered by fatigue. In conclusion, due to the potential risk of loss of balance, it is important to take the role of plantar flexor muscle fatigue into account during more difficult postural tasks.

Electromyography (EMG) signal processing and Muscle Onset Latency (MOL) are widely used in rehabilitation sciences and nerve conduction studies. The majority of existing software packages provided for estimating MOL via analyzing EMG signal are computerized, desktop based and not portable; therefore, experiments and signal analyzes using them should be completed locally. Moreover, a desktop or laptop is required to complete experiments using these packages, which costs. Develop a non-expensive and portable Android application (app) for estimating MOL via analyzing surface EMG. A multi-layer architecture model was designed for implementing the MOL estimation app. Several Android-based algorithms for analyzing a recorded EMG signal and estimating MOL was implemented. A graphical user interface (GUI) that simplifies analyzing a given EMG signal using the presented app was developed too. Evaluation results of the developed app using 10 EMG signals showed promising performance; the MOL values estimated using the presented app are statistically equal to those estimated using a commercial Windows-based surface EMG analysis software (MegaWin 3.0). For the majority of cases relative error <10%. MOL values estimated by these two systems are linearly related, the correlation coefficient value ~ 0.93. These evaluations revealed that the presented app performed as well as MegaWin 3.0 software in estimating MOL. Recent advances in smart portable devices such as mobile phones have shown the great capability of facilitating and decreasing the cost of analyzing biomedical signals, particularly in academic environments. Here, we developed an Android app for estimating MOL via analyzing the surface EMG signal. Performance is promising to use the app for teaching or research purposes.

Nowadays, more than 10,000 different types of medical devices can be found in hospitals.These devices used in medical centers and hospitals for monitoring and treatment of patients require periodic safety and performance checking in order to have confidence in their functioning and operation. Physicians need better accurate medical measurements in order to better diagnose diseases, monitor patients and deliver treatments, in this way failure to ensure appropriate measurements will certainly have diverse effects. Safety and performance testing of medical devices in the medical sector is a one of the key factor in improving public health. Acquiring results of some investigations indicate a need for new and severe regulations on periodic performance verifications and medical equipment quality control program especially in highrisks instruments.The metrological reliability of four high risk medical devices, Electrosurgical unit, Defibrillator, Syringe pump and Infant incubator in use some hospitals (privates and publics) in one of the province of Iran according to international and national standards was evaluated. Quantitative analysis of Some parameters that impact the safety and performance showed the amount of the obtained results in some equipment are in critical range and have higher values than standard limitations. General electrical safety evaluations for measuring the patient leakage currents and patient auxiliary currents carried out for all of groups,in some cases the amount of leakage currents were over the standard limitations.Acquiring results indicate a need for new and severe regulations on periodic performance verifications and medical equipment quality control program especially in high risk instruments. It is also necessary provide training courses for operating staff in the field of meterology in medicine and what’s the critical parameters and how they can get good accuracy results equipment.