فهرست مطالب

Medical Physics - Volume:13 Issue: 3, Summer 2016

Iranian Journal of Medical Physics
Volume:13 Issue: 3, Summer 2016

  • تاریخ انتشار: 1395/07/09
  • تعداد عناوین: 8
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  • Bagher Farhood, Mohammad Taghi Bahreyni Toossi *, Shokouhozaman Soleymanifard Pages 146-153
    Introduction
    Wedge modifiers are commonly applied in external beam radiotherapy to change the dose distribution corresponding to the body contour and to obtain a uniform dose distribution within the target volume. Since the radiation dose delivered to the target must be within ±5% of the prescribed dose, accurate dose calculation by a treatment planning system (TPS) is important. The objective of the present study was to quantify the dose calculation accuracy of TiGRT TPS for physical wedged fields in radiotherapy.
    Materials And Methods
    A Semiflex™ ionization chamber was used for dose measurements in a water phantom; TiGRT TPS was also applied for dose calculations. The central axis (i.e., high dose-small dose gradient), build-up (i.e., high dose-large dose gradient), off-axis (i.e., high dose-small dose gradient), and out-of-field (i.e., low dose-small dose gradient) regions were evaluated in this study. Finally, the confidence limit values were obtained to quantify the dose calculation accuracy of TPS in these regions.
    Results
    The confidence limit values for the central axis, build-up, off-axis, and out-of-field regions were 1.01, 8.62, 1.79, and 55.24, respectively. Furthermore, the results showed that TiGRT TPS underestimated the dose of build-up and out-of-field regions for most points.
    Conclusion
    According to the results of the present study, it can be concluded that the dose calculation accuracy of TiGRT TPS for physical wedged fields in the central axis, build-up, and off-axis regions is adequate, while it is insufficient for out-of-field regions.
    Keywords: Accuracy, Dose, Radiotherapy, Treatment Planning, Wedge
  • Lida Gholamkar, Mahdi Sadeghi, Ali Asghar Mowlavi *, Mitra Athari Pages 154-162
    Introduction
    One of the best methods in the diagnosis and control of breast cancer is mammography. The importance of mammography is directly related to its value in the detection of breast cancer in the early stages, which leads to a more effective treatment. The purpose of this article was to calculate the X-ray spectrum in a mammography system with Monte Carlo codes, including MCNPX and MCNP5.
    Materials And Methods
    The device, simulated using the MCNP code, was Planmed Nuance digital mammography device (Planmed Oy, Finland), equipped with an amorphous selenium detector. Different anode/filter materials, such as molybdenum-rhodium (Mo-Rh), molybdenum-molybdenum (Mo-Mo), tungsten-tin (W-Sn), tungsten-silver (W-Ag), tungsten-palladium (W-Pd), tungsten-aluminum (W-Al), tungsten-molybdenum (W-Mo), molybdenum-aluminum (Mo-Al), tungsten-rhodium (W-Rh), rhodium-aluminum (Rh-Al), and rhodium-rhodium (Rh-Rh), were simulated in this study. The voltage range of the X-ray tube was between 24 and 34 kV with a 2 kV interval.
    Results
    The charts of changing photon flux versus energy were plotted for different types of anode-filter combinations. The comparison with the findings reported by others indicated acceptable consistency. Also, the X-ray spectra, obtained from MCNP5 and MCNPX codes for W-Ag and W-Rh combinations, were compared. We compared the present results with the reported data of MCNP4C and IPEM report No. 78 for Mo-Mo, Mo-Rh, and W-Al combinations.
    Conclusion
    The MCNPX calculation outcomes showed acceptable results in a low-energy X-ray beam range (10-35 keV). The obtained simulated spectra for different anode/filter combinations were in good conformity with the finding of previous research.
    Keywords: Anodes, Filters, Full, field digital mammography system, MCNP code, Monte Carlo Method, X-ray spectrum
  • Atefeh Goshvarpour, Ataollah Abbasi *, Ateke Goshvarpour, Sabalan Daneshvar Pages 163-173
    Introduction
    To extract and combine information from different modalities, fusion techniques are commonly applied to promote system performance. In this study, we aimed to examine the effectiveness of fusion techniques in emotion recognition.
    Materials And Methods
    Electrocardiogram (ECG) and galvanic skin responses (GSR) of 11 healthy female students (mean age: 22.73±1.68 years) were collected while the subjects were listening to emotional music clips. For multi-resolution analysis of signals, wavelet transform (Coiflets 5 at level 14) was used. Moreover, a novel feature-level fusion method was employed, in which low-frequency sub-band coefficients of GSR signals and high-frequency sub-band coefficients of ECG signals were fused to reconstruct a new feature. To reduce the dimensionality of the feature vector, the absolute value of some statistical indices was calculated and considered as input of PNN classifier. To describe emotions, two-dimensional models (four quadrants of valence and arousal dimensions), valence-based emotional states, and emotional arousal were applied.
    Results
    The highest recognition rates were obtained from sigma=0.01. Mean classification rate of 100% was achieved through applying the proposed fusion methodology. However, the accuracy rates of 97.90% and 97.20% were attained for GSR and ECG signals, respectively.
    Conclusion
    Compared to the previously published articles in the field of emotion recognition using musical stimuli, promising results were obtained through application of the proposed methodology.
    Keywords: Electrocardiogram, Emotion, Galvanic Skin Responses, Neural Networks, Wavelet Analyses
  • Reza Pourimani *, Hamid Reza Azimi Pages 174-182
    Introduction
    Iron ore is one of the most important natural raw materials that is widely used for manufacturing iron and steel. This type of ore contains various amounts of radionuclides; thus, exposing workers handling their extraction, transportation, and processing to radiation.
    Materials And Methods
    In this study, 12 ore samples (each mass weighing about 2 kg) were collected from the iron ore mining areas of Arak region, Iran. The specific activities of 226Ra, 232Th, and 40K were determined usinggamma-ray spectrometry method employing high-purity germanium (HPGe) detector.
    Results
    The specific activities of 226Ra, 232Th, and 40K in samples were 9.39-271.70 Bq/kg, -3 Sv/y) suggested in International Commission of Radiological Protection (ICRP) Publication 82.
    Conclusion
    The gamma ray spectrometric analysis showed that the specific activities of natural radionuclides in samples, except for limonite ore, were within the worldwide range. The effective dose received by workers was much lower than the maximum acceptable value (1000 μSv/y); therefore, the level of radiations in this mine had no adverse consequences for public health.
    Keywords: Dose assessment, Iron ore, Natural radiation, Radionuclide
  • Seyed Ali Shafiei * Pages 183-192
    Introduction
    Many features, emerging from mathematical techniques, have been used in the analysis of brain signals. In this study, the physical quantity of “moment of inertia” (MOI) was introduced as a feature to enhance high-frequency waves (HFWs) in electroencephalography (EEG).
    Materials And Methods
    In this research, the recorded EEGs from F3, F4, and Cz points in 20 males were used. A total of 30 noiseless epochs (4 sec with a 1 sec overlap) were selected for each eyes-open and eyes-closed state from each brain signal. After averaging the relative power spectrum (RPS) of 30 epochs and obtaining an RPS with low fluctuation, the MOIs of the power spectrum and each EEG band were calculated.
    Results
    The MOI enhanced the HFWs of brain signals; therefore, HFW fluctuations in the power spectrum of MOI were more evaluable and observable than those of RPS. Paired t-test showed no significant difference in the asymmetry of MOI between the eyes-open and eyes-closed states (P=0.227), while the MOIs of alpha and beta bands between these two states were significantly different [F(1, 38)=11.8; P=0.001 and F(1, 38)=12.9; P=0.001, respectively].
    Conclusion
    This study demonstrated that the MOI of different frequency bands might be used as a feature for some patients who are different from healthy subjects in terms of high-frequency bands or performance of two hemispheres. Therefore, in order to ensure the applicability of the obtained results, evaluation of MOI for EEG of some disorders, such as attention-deficit hyperactivity disorder, alcoholism, and autism is suggested in future studies.
    Keywords: Beta Rhythm, Brain Waves, Digital Signal Processing, Asymmetry
  • Sayyede Batoul Shokouhian, Alireza Karimian*, Mohammad Mohammad, Zadeh, Hamid Reza Salighe, Rad Pages 193-202
    Introduction
    Radiofrequency planar microcoils are used to increase the resolution of magnetic resonance images of small samples. In this study, we aimed to design and fabricate a spiral planar microcoil constructed on a double-sided printed circuit board (PCB). It has four rings with an internal diameter of 241 microns tuned and matched at 63.8 MHz.
    Materials And Methods
    To achieve the maximum signal-to- noise ratio (SNR) and quality factor of the coil, its geometry was optimized based on parameters such as width (w) and thickness (h) of the copper rings, the distance between the rings, inner radius of the microcoil (Ri), and the number (N) of coil rings by using COMSOL, ADS, and MATLAB software packages.
    Results
    Our findings indicated that the Q factor and SNR of the coil at resonance frequency of 63.8 MHz are 63.149 and 168.23, respectively, which are higher than the equivalent features of the pervious coils. In addition, to evaluate the function of matching and tuning circuit, reflection coefficient factor (S11) of the coil was experimentally measured to be -48 dB at resonance frequency of 63.8 MHz, which is consistent with the simulated value.
    Conclusion
    In this study, a new microcoil was designed and fabricated to produce images of very small samples and volumes in microliter dimensions. The results showed that this new microcoil has superior capability in imaging very small samples compared to the conventional coils applied in magnetic resonance imaging devices.
    Keywords: Nuclear magnetic resonance, Radiofrequency microcoil, Signal to noise ratio
  • Seyed Milad Vahabi *, Mojtaba Shamsaei Zafarghandi Pages 203-210
    Introduction
    Dose calculation of tumor and surrounding tissues is essential during prostate brachytherapy. Three radioisotopes, namely, 125I, 103Pd, and 131Cs, are extensively used in this method. In this study, we aimed to calculate the received doses by the prostate and critical organs using the aforementioned radioactive seeds and to investigate the effect of scattering contribution for the legs on dose calculations.
    Materials And Methods
    The doses to organs of interest were calculated using MCNPX code and ORNL (Oak Ridge National Laboratory) phantom.
    Results
    Doses to the prostate as a source of radiation for 125I, 103Pd, and 131Cs were approximately 108.9, 97.7, and 81.5 Gy, respectively. Bladder, sigmoid colon, and testes received higher doses than other organs due to proximity to the prostate. Differences between the doses when tallying with the legs intact and with the legs voided were significant for testes, sigmoid colon contents, and sigmoid colon wall because of their proximity to the prostate. There was also a good consistency between our results and the data published by Montefiore Medical Center and Albert Einstein College of Medicine for the prostate.
    Conclusion
    Scattering from leg region had a significant effect on doses to testes, sigmoid colon contents, and sigmoid colon wall in the pelvic region, and prostate and the other organs were unaffected. Brachytherapy treatment plans using 131Cs seeds allow for better sparing of critical tissues, with a comparable number of, or fewer, seeds required, compared to 125I seeds.
    Keywords: Brachytherapy, Monte Carlo, Prostate, Scattering, Phantom
  • Alireza Vejdani, Noghreiyan, Atiyeh Ebrahimi, Khankook* Pages 211-217
    Introduction
    Accurate estimation of the absorbed dose in radiosensitive organs, located away from the target volume during radiotherapy, is one of the main reasons for the development of reference phantoms. The International Commission on Radiological Protection (ICRP) reference phantoms can provide a more realistic view of the human anatomy in comparison with the previously used mathematical phantoms. However, the ICRP reference phantoms seem to have certain limitations, resulting in the inaccurate eye simulation due to the absence of super-high-resolution CT scan images.
    Materials And Methods
    In this study, we developed a modified version of the ICRP reference phantom by inserting a realistic eye phantom into the voxelized phantom. In addition, by using the developed model, the absorbed dose received by sensitive organs (e.g., thyroid, brain, and different parts of the eye) during radiotherapy of a common ocular surface tumor was determined. The results were compared with those obtained by the modified phantom developed by the University of Florida-Oak Ridge National Laboratory (UF-ORNL).
    Results
    Based on the results, the relative difference between the equivalent doses calculated by the developed phantom and UF-ORNL phantom was nearly 75-95% and 3% for thyroid and eye substructures, respectively.
    Conclusion
    Despite of many advantageous of voxel phantoms, they have considerable limitation in providing accurate model of the eye. In the present study, a detailed stylized model was developed and incorporated into the Adult Male (AM) reference and UF-ORNL phantoms. These phantoms were then used for the dosimetric calculations during eyelid cancer therapy.
    Keywords: Dosimetry, Eye, Mathematical model, Radiotherapy