Iranian Journal of Medical Physics
Volume:7 Issue: 27, 2010

Orthogonal radial fields are those in which the central axes are perpendicular to each other. An example of these orthogonal fields is the set of craniospinal orthogonal fields that are used for radiotherapy of medulloblastoma. Craniospinal radial fields consist of two parallel-opposed fields for brain exposure and one or two posterior spinal fields for spinal cord exposure. The main problem in using these combinative fields is the overlap of radial fields, where they adjoin. Therefore, adjusting radial fields in craniospinal radiotherapy is of remarkable significance and can outstandingly affect the reduction of the side effects due to radiotherapy. In doing so, two different setups were used for craniospinal radiotherapy, and by using dosimetry in each adjustment in the junction region between brain and upper spine fields and in organs at risk, the results of the two adjustments were compared. Each one of these two setups was separately performed on a Rando phantom. In the first setup, the arrangement of radial fields was performed without the rotation of the treatment bed and the collimators of the brain fields. In the second setup, the arrangement of radial fields was performed using the rotation of the treatment bed and the collimators of brain fields. For dosimetry, GR-200 TLDs were used. For radiotherapy, a varian linac (2100 C/D Model) was used. The results of dosimetry in the brain CTV, junction of brain and upper spine fields, thyroid and heart in the first setup were equal to 105, 168, 46 and 44 cGy, respectively, and in second setup, 106, 140, 48 and 44 cGy, respectively. Absorbed dose to the testes in both setups was negligible. Discussion and The results of dosimetry in both setups showed that angling the bed and the collimators for the brain fields prevents the overlap of radial fields and reduces the side effects due to radiotherapy.

In Single Photon Emission Computed Tomography (SPECT), the projection data used for image reconstruction are distorted by several factors, including attenuation and scattering of gamma rays, collimator structure, data acquisition method, organ motion, and washout of radiopharmaceuticals. All these make reconstruction of a quantitative SPECT image very difficult. Simulation of a SPECT system is a convenient method to assess the impact of these factors on the image quality. The SIMIND Monte Carlo program was employed to simulate a Siemens E.CAM SPECT system. Verification of the simulation was performed by comparing the performance parameters of the system. The verified system was used for SPECT simulations of homogenous and inhomogeneous voxelized phantoms in conjugation with hardware modifications. The resulting data were compared with those obtained from the simulated system without any modifications. Image quality was assessed by comparing the Structural SIMularity index (SSIM), contrast, and resolution of images. The energy spectra acquired from both simulated and real SPECT systems demonstrated similar energy peak regions. The resulting full-widths-at-half-maximums were 13.92 keV for the simulation and 13.58 keV for experimental data, corresponding to energy resolutions of 9.95% and 9.61%, and with calculated sensitivities of 85.39 and 85.11 cps/MBq, respectively. Better performance parameters were obtained with a hardware-modified system constructed using a 0.944 cm thickness NaI(Tl) crystal covered by a layer of 0.24 cm aluminum, a slat of 4.5 cm Pyrex as a backscattering medium, and a parallel hole collimator of Pb-Sb alloy with 2.405 cm thickness.The modeling of a Siemens E.CAM SPECT system was performed with the SIMIND Monte Carlo code. Results obtained with the code are in good agreement with experimental results. The findings demonstrate that the proposed hardware modifications in the system appear to be suitable for further improvement of the performance parameters of the system, indicating that future investigations can be conducted on using the system for supplementary studies on image improvement in the field of nuclear medicine.

Appropriate definition of the distance measure between diffusion tensors has a deep impact on Diffusion Tensor Image (DTI) segmentation results. The geodesic metric is the best distance measure since it yields high-quality segmentation results. However, the important problem with the geodesic metric is a high computational cost of the algorithms based on it. The main goal of this paper is to assess the possible substitution of the geodesic metric with the Log-Euclidean one to reduce the computational cost of a statistical surface evolution algorithm. We incorporated the Log-Euclidean metric in the statistical surface evolution algorithm framework. To achieve this goal, the statistics and gradients of diffusion tensor images were defined using the Log-Euclidean metric. Numerical implementation of the segmentation algorithm was performed in the MATLAB software using the finite difference techniques. In the statistical surface evolution framework, the Log-Euclidean metric was able to discriminate the torus and helix patterns in synthesis datasets and rat spinal cords in biological phantom datasets from the background better than the Euclidean and J-divergence metrics. In addition, similar results were obtained with the geodesic metric. However, the main advantage of the Log-Euclidean metric over the geodesic metric was the dramatic reduction of computational cost of the segmentation algorithm, at least by 70 times.Discussion and The qualitative and quantitative results have shown that the Log-Euclidean metric is a good substitute for the geodesic metric when using a statistical surface evolution algorithm in DTIs segmentation.

Secondary radiation such as photoelectrons, Auger electrons and characteristic radiations cause a local boost in dose for a tumor when irradiated with an external X-ray beam after being loaded with elements capable of activating the tumor, e.g.; I and Gd.In this investigation, the MCNPX code was used for simulation and calculation of dose enhancement factor for a tumor loaded with activating elements. The designed model comprised the X-ray source, phantom (target tissue and loaded tumor with activating agent), detector, interactions modeling and results. The source was defined as monochromatic and plane surface situated at 50 cm (z = 50). Phantom geometry was a 10 × 10 × 10 cm3 cube centered at (0, 0, 0) with a 2.2 × 2.2 × 2.2 cm3 cubic tumor with a center located at 3 cm depth inside the phantomDose enhancement factor and optimum energy in radiotherapy are evaluated using the photon activation therapy method. Result show that the dose enhancement factor increases with activating concentration in the tumor. The maximum dose enhancement factor for iodine in the tumor occurs for photons in the energy range of 50-60 keV. Dose uniformity is less for lower energy photons within the activated region inside the tumor. Results indicate that the dose enhancement factor varies linearly with the activating concentration agent.Discussion and In this study, the obtained results point out a considerable enhancement in dose in the presence of activating agents in the tumor regions.

Recent industrial developments in human societies have caused rapid advancements in technologies of production and distribution of electricity, which in turn result in enhancement of power networks and utilization of high voltages. These networks and the high voltages in transfer lines cause the exposure to electric and magnetic fields. In this study, the situation regarding the magnetic fields from high-voltage (230 kV) substations in Tehran was investigated. In this study, 8 high-voltage (230 kV) substations were selected (Shous, Shahid Firouzi, Ozgol, Kan, Tehranpars, Azadegan, Ghorkhane and Besat substations). The premises of each substation was divided into some stations and measurements were done in each one. Measurements were done according to the IEEE std 644-1994 Standard in a way that the device, specifically its probe, was kept at a height of 1 meter above the ground surface. Then, we tried to examine the probable effects of exposure to magnetic fields through the Essex questionnaire, with Cronbach coefficient of 94%, completed by the employees of the substations. These questionnaires were completed by substation operators as an exposed group (36 persons) and the employees of the office section of the Tehran regional electric company as a witness group (32 persons). The measured density in none of the stations exceeded the standard limits of the International Commission on Non-Ionizing Radiation Protection. With regard to the questionnaire results about mental and neurological, cardiac and respiratory, and gastrointestinal and auditory disorders, we observed significant differences between witness and exposed groups, however, regarding skin allergies, there was no significant difference. Among all control rooms, the highest measured magnetic field was 6.9 mG in the Ozgol Substation Control Room and the lowest was 2 mG in the post of Shahid Firouzi. The control room of Ozgol substation is located on the second floor and bus-bars are located at a short distance from the eastern window, so the highest recorded magnetic field was measured in that control room. Among all switchgear parts, the highest field of 91.5 mG was measured in the Kan substation. In spite of accordance of the magnetic fields with the standards (based on measurements), it can be seen that exposure to magnetic fields at high-voltage (230 kV) substations causes the intensification of neurological and mental, cardiac and respiratory, gastrointestinal and auditory disorders but it has no effect on skin allergies

Gamma Knife is an instrument specially designed for treating brain disorders. In Gamma Knife, there are 201 narrow beams of cobalt-60 sources that intersect at an isocenter point to treat brain tumors. The tumor is placed at the isocenter and is treated by the emitted gamma rays. Therefore, there is a high dose at this point and a low dose is delivered to the normal tissue surrounding the tumor. In the current work, the MCNP simulation code was used to simulate the Gamma Knife. The calculated values were compared to the experimental ones and previous works. Dose distribution was compared for different collimators in a water phantom and the Zubal brain-equivalent phantom. The dose profiles were obtained along the x, y and z axes. The evaluation of the developed code was performed using experimental data and we found a good agreement between our simulation and experimental data. Our results showed that the skull bone has a high contribution to both scatter and absorbed dose. In other words, inserting the exact material of brain and other organs of the head in digital phantom improves the quality of treatment planning. This work is regarding the measurement of absorbed dose and improving the treatment planning procedure in Gamma-Knife radiosurgery in the brain.

Today, facial bio-potential signals are employed in many human-machine interface applications for enhancing and empowering the rehabilitation process. The main point to achieve that goal is to record appropriate bioelectric signals from the human face by placing and configuring electrodes over it in the right way. In this paper, heuristic geometrical position and configuration of the electrodes has been proposed for improving the quality of the acquired signals and consequently enhancing the performance of the facial gesture classifier. Investigation and evaluation of the electrode's proper geometrical position and configuration can be performed using two clinical and modeling. In the clinical method, the electrodes are placed in predefined positions and the elicited signals from them are then processed. The performance of the method is evaluated based on the results obtained. On the other hand, in the modeling approach, the quality of the recorded signals and their information content are evaluated only by modeling and simulation. In this paper, both methods have been utilized together. First, suitable electrode positions and configuration were proposed and evaluated by modeling and simulation. Then, the experiment was performed with a predefined protocol on 7 healthy subjects to validate the simulation results. Here, the recorded signals were passed through parallel butterworth filter banks to obtain facial EMG, EOG and EEG signals and the RMS features of each 256 msec time slot were extracted. By using the power of Subtractive Fuzzy C-Mean (SFCM), 8 different facial gestures (including smiling, frowning, pulling up left and right lip corners, left/right/up and down movements of the eyes) were discriminated. According to the three-channel electrode configuration derived from modeling of the dipoles effects on the surface electrodes and by employing the SFCM classifier, an average 94.5% discrimination ratio was obtained. The results can validate our hypothesis and the simulation results too.Discussion and Based on the obtained results, it is clear that our proposed electrode configuration and placement is an efficient method which can be used for further applications such as designing and implementing a robust human-machine interface.

GafChromic EBT films are one of the self-developing and modern films commercially available for dosimetric verification of treatment planning systems (TPSs). Their high spatial resolution, low energy dependence and near-tissue equivalence make them suitable for verification of dose distributions in radiation therapy. This study was designed to evaluate the dosimetric parameters of the RtDosePlan TPS such as PDD curves, lateral beam profiles, and isodose curves measured in a water phantom using EBT Radiochromic film and EGSnrc Monte Carlo (MC) simulation.Methods and Materials: A Microtek color scanner was used as the film scanning system, where the response in the red color channel was extracted and used for the analyses. A calibration curve was measured using pieces of irradiated films to specific doses. The film was mounted inside the phantom parallel to the beam's central axis and was irradiated in a standard setup (SSD = 80 cm, FS = 10×10 cm2) with a 60Co machine. The BEAMnrc and the DOSXYZnrc codes were used to simulate the Co-60 machine and extracting the voxel-based phantom. The phantom's acquired CT data were transferred to the TPS using DICOM files. Distance-To-Agreement (DTA) and Dose Difference (DD) among the TPS predictions, measurements and MC calculations were all within the acceptance criteria (DD=3%, DTA=3 mm). This study shows that EBT film is an appropriate tool for verification of 2D dose distribution predicted by a TPS system. In addition, it is concluded that MC simulation with the BEAMnrc code has a suitable potential for verifying dose distributions.