فهرست مطالب

Medical Physics - Volume:15 Issue: 3, Summer 2018

Iranian Journal of Medical Physics
Volume:15 Issue: 3, Summer 2018

  • تاریخ انتشار: 1397/04/28
  • تعداد عناوین: 10
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  • Samaneh Babazadeh Toloti, Laleh Rafat Motavalli *, Hashem Miri Hakimabad, Samira Mohammadi-Yeganeh, Eftekhar Rajab-Bolokat Pages 132-139
    Introduction
    The aim of the present study was to assess the radiosensitivity parameters for SK-BR-3 (SKBR3) breast cancer cells that could be implemented in the cutting-edge treatment planning systems (TPS) for accelerated partial-breast irradiation (APBI).
    Materials And Methods
    The cell survival fraction and its relevant radiosensitivity coefficients, namely α and β, in linear-quadratic (LQ) formalism were evaluated for 6 MV X-rays and 60Co γ-rays using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. During the irradiation time, the medium temperature was kept at 4°C to prevent the repair of sublethal radiation damages over the exposure time and keep the survival fractions independent of the dose rate.
    Results
    Fitting the LQ model to experimental data, α, β, and α/β radiosensitivity parameters were obtained as 0.156±0.027 Gy-1, 0.026±0.007 Gy-2,and 6.0 Gy for 6 MV X-rays and 0.162±0.028 Gy-1, 0.028±0.007 Gy-2, and 5.8 Gy for 60Co gamma radiation, respectively. The average relative biological effectiveness (RBE) values were 0.91 and 0.96 for 6 MV X-rays and 60Co γ-rays, respectively. The derived LQ parameters were also compared with those previously obtained from in vitro studies for different breast cancer cell lines using various regimes, such as radiotherapy modality with different dose rates and delivered doses.
    Conclusion
    The results of this study provided essential constant values for α and β parameters. The data could be useful for the improvement of TPS to include the effect of different biological responses to radiation in APBI treatment plans.
    Keywords: Radiotherapy, Relative Biological, Effectiveness, Cell Survival, In Vitro Techniques
  • Mohammad Taghi Bahreyni Toossi, Hamid Gholamhosseinian, Atefeh Vejdani Noghreiyan* Pages 140-145
    Introduction
    In radiation therapy, knowing the dose rates to healthy organs and tumors is beneficial, and thermoluminescent dosimeter (TLD) allows for this possibility. This study was aimed at determining the dose-response differences of TLDs in various types of radiation, energy levels, and dose rate calibrated with other types of radiation beams and energy and dose levels.
    Materials And Methods
    In this study, LiF:Mg,Ti (TLD-100) was used for dosimetry. Photon and electron irradiation was performed by Elekta Precise Linear Accelerator. First, TLDs were calibrated in three different groups of 6 MV photon, 6 MeV electron, and 60Co teletherapy photon beam with 50 cGy dose. Next, each group was irradiated with 6 MV photon, 6 MeV electron, and 60Co teletherapy photon beam separately at three different dose levels of 20, 60, and 100 cGy.
    Results
    TLDs calibrated with electron were significantly different at all dose levels and with all types of radiation from TLDs calibrated with photon or 60Co teletherapy photon beam (P=0.000). P-value of the TLDs calibrated with 6 MV photon versus 60Co was less than 0.94. The maximum standard deviation belonged to 100 cGy irradiation, while the least pertained to 20 cGy irradiation.
    Conclusion
    Calibration of TLDs depends on the type of radiation.
    Keywords: Calibration, Dosimetry, Energy, Irradiation, TLD
  • Deepak Basandrai *, Amarjot Dhami Pages 146-150
    Introduction
    The present study aimed to present a numerical analysis of the penetration depth, specific absorption rate (SAR), and temperature rise in various eye tissues with varying distance between radiation source and exposed human eye tissues (i.e., cornea, posterior chamber, anterior chamber, lens, sclera, vitreous humor, and iris) at frequencies of 900 and1800 MHz.
    Materials And Methods
    A theoretical model was proposed based on the tissue dielectric and thermal properties, Maxwell equations, Joules law of heating, and microscopic form of Ohm's law to find the realistic situation of the cell phone radiation interaction with various human eye tissues.
    Results
    According to the results, the anterior chamber had the highest temperature rise, compared to the vitreous, sclera, lens, cornea, and posterior chamber. By assuming the distance of 5 cm and exposure time of 30 min, the maximum rise in temperature for the anterior chamber was estimated to be 1.2°C and 2.2°C for 900 and 1,800 MHz frequencies, respectively.
    Conclusion
    As the findings indicated, the anterior chamber had the maximum rise in temperature, compared to other investigated tissues. This could be due to the disposal of excess heat by the perfusion of the blood in the vitreous, posterior chamber, sclera, and lens tissues and the cooling effects produced due to convection/conduction in the cornea tissue. However, the anterior chamber tissue had no such mechanism for heat disposal.
    Keywords: Human Eye, Temperature Elevation, Radiation Effects
  • Homa Hassankarimi, Ebrahim Jafarzadehpur *, Alireza Mohamadi, Seyed Mohammad Reza Noori Pages 151-160
    Introduction
    to identify the pattern-reversal visual evoked potential (PRVEP) waveform descriptor by evaluating discrete wavelet transform (DWT) in order to optimize stimulus in the diagnosis of anisometropia amblyopia.
    Materials And Methods
    The PRVEP testing was performedfor 31 normal individuals and 35 patients with amblyopia. The stimuli were consisted of spatial frequencies of 1, 2, and 4 cycles per degree (cpd) and contrast levels of 100%, 50%, 25%, and 5%. The results were analyzed in the dimensions of time and time-frequency. DWT descriptor were extracted at level 7 (7P descriptor) for Haar, Daubechies 2, Daubechies 4, Symlet 5, Biorthogonal 3.5, Biorthogonal 4.4, and Coiflet 5 wavelets for 12 stimuli and compared between the two groups. The correlation between different spatial frequencies at the same contrast level and the similarities between reconstructed signals and original waveforms were evaluated.
    Results
    There were a significant reduction in P100 amplitude and a significant elevation in latency among the patient group. In the patients with amblyopia, 7P descriptor decreased in all analysis except for the frequency of 4 cpd and the contrast of 5% using bior4.4. No significant correlation was observed between different frequencies at a special contrast; however, there was a significant correlation between reconstructed signals and the original ones.
    Conclusion
    The 7P descriptor could be used to distinguish between normal and abnormal signals in anisometropia amblyopia. Considering the results, DWT with coif5, db4, bior4.4, and bior3.5 wavelets can be utilized as a good indicator for selecting optimum stimulus.
    Keywords: Anisometropia, Amblyopia, Wavelet Analysis, Dimension of Time
  • Armin Imanparast, Neda Attaran, Ameneh Sazgarnia * Pages 161-168
    Introduction
    Hollow gold nanoshells (HAuNS) are one of the most attractive nanostructures for biomedical applications due to their interesting physicochemical properties. This study sought to evaluate the plasmonic photothermal effect of HAuNS irradiated with incoherent light on melanoma cell line.
    Materials And Methods
    After the synthesis of nanostructures, the temperature changes of HAuNS and polyethylene glycol stabilized HAuNS (HAuNS-PEG) were evaluated at different irradiation dose levels. After determining the potential cytotoxicity of the agents, the DFW cells were irradiated by incoherent light with and without the nanostructures at different exposure doses with two spectral bands of 670±25 nm and 730±25 nm. Finally, the rate of the cell survival was determined by 1-Methyltetrazole-5-Thiol assay 24 h after irradiating.
    Results
    The HAuNS, HAuNS-PEG, and light exposure did not have any significant effect on the cell survival, individually. Stabilizing with PEG led to an increase in size and decreased their polydispersity index, zeta potential, and conductivity. The slopes of temperature and cell death caused by 730 nm were greater than 670 nm when the cells were irradiated in the presence of nanostructures. These changes became more significant with increasing the dose of exposure and HAuNS (or HAuNS-PEG) concentration. The lowest cell survival occurred in the concentration of 250 μg/ml of nanostructures and an exposure dose of 9 min (P
    Conclusion
    the HAuNS-PEG significantly reduced its conductivity that leads to decreased plasmonic photothermal effect. Additionally, using an incoherent light with more spectral overlap for irradiating the nanostructures increased its thermal effects.
    Keywords: Polyethyleneglycol, Nanoshell, Photothermal Therapy, Incoherent Light
  • Zahra Kavousi, Alireza Karimian*, Iraj Jabbari Pages 169-175
    Introduction
    Crosstalk is a leakage of X-ray or light produced in a matrix of X-ray detectors or array of photodiodes in one element to other elements affecting on image contrast and spatial resolution. In this study, we assessed X-ray crosstalk in a computed tomography (CT) scanner with small detector elements to estimate the effect of various parameters such as X-ray tube voltage, detector element sizes, scintillator material, impurities in the scintillator material, and the material of detector separators on X-ray crosstalk.
    Materials And Methods
    This study was performed using Monte Carlo simulation. In the first step, X-ray tube and its energy spectrum at the energies of 80, 100, 120, and 140 keV were simulated and validated by using SpekCalc and t-test. Then, other important parts of CT scanner, namely filters, detectors, and grids were simulated. X-ray crosstalk between CT detectors was calculated in air and in the presence of water phantom (as a simulator of human body) to compare the effect of scattered photons. Finally, the influence of some important parameters on X-ray crosstalk was evaluated.
    Results
    In CT scanner with small elements, when using phantom, crosstalk increases by 16-50%. Using the lowest possible energies of X-ray, decreases the crosstalk up to 43% of its initial amount. Furthermore coating a 10 or 20 µm layer of tungsten or lead on the detector separators, decreases the X-ray crosstalk significantly.
    Conclusion
    Choosing the proper high voltage, detectors’ material and its dimensions, scintillator impurities and septa material can decrease X-ray crosstalk.
    Keywords: Computed tomography, Detector, Monte Carlo Method, Phantom
  • Hamed Masoumi, Hadi Hasanzadeh*, Majid Jadidi, Majid Mirmohammadkhani, Ahmad Bitarafan-Rajabi, Ali Abedelahi, Alireza Emadi, Mitra Bokharaeian, Fatemeh Shabani, Shima Moshfegh, Danial Seifi, Tahereh Khani, Mohammad Pursamimi, Athar Ehtiati, Mohammad Hosein Vali, Abbas Ziari Pages 176-182
    Introduction
    Radiation exposure during radiological examination is a health concern, of which radiology professionals should be cognizant. We sought to evaluate the radiation protection knowledge, attitudes, and practice (KAP) amongst radiology staff of hospitals across 10 provinces of Iran.
    Materials And Methods
    For evaluating the level of radiation protection KAP, 553 radiology staff were enrolled. A 32-item questionnaire was designed to assess radiation protection KAP, the validity which was confirmed by members of the Medical Physics and Biostatistics departments. The questionnaire evaluated the respondent's knowledge, practice, and attitudes towards the basic principles of radiation protection, the necessity of using protective equipment, and their performance in the implementation of radiation protection recommendations.
    Results
    We found no significant difference in the level of radiation protection KAP between male and female radiology staff and among those with different educational levels and ages (P>0.05). However, there was a significant association between radiation protection KAP and working experience, hospital size, and hospital type (P0.05).
    Conclusion
    Our results showed that the level of radiation protection KAP among radiology staff is inadequate. This might be due to the lack of ongoing training courses concerning protection against ionizing radiation. Thus, sustained training of radiation protection principles can promote KAP among the staff of radiology departments, and in turn, reduce public dose from medical diagnostic modalities.
    Keywords: Knowledge Attitude, Professional Practice, Radiation Protection, Medical Staff
  • Seyed Alireza Mousavi Shirazi * Pages 183-191
    Introduction
    The present study was conducted with the aim of designing a liver phantom for dosimetry. To benchmark the results obtained by the developed liver phantom, another method was applied for the dosimetry of a real liver tissue using imaging.
    Materials And Methods
    For the purpose of the study, a real liver tissue was converted into a phantom based on thegram-molecular weight of the components of human liver tissue, mass percentage, and density, and then simulated by MCNPX code for dosimetry. The real liver tissue was contoured using the computed tomography DICOM images of the abdomen region. Subsequently, the accurate geometry of the segmented liver tissue was generated and simulated by MATLAB software and MCNPX code for dosimetric purposes. Then, the obtained data were transferred into the MCNPX code.
    Results
    Equivalent dose was measured in total and for each component of the liver phantom and separated liver tissue. The results obtained from these two simulations were compared with each other to validate the efficiency of the phantom and evaluated the differences.
    Conclusion
    The comparison of the equivalent doses obtained from the prepared equivalent liver phantom and the real liver tissue revealed the applicability of the liver phantom as a virtual liver for dosimetry.
    Keywords: Computed tomography, Dosimetry, Imaging, Liver, Phantom
  • Reza Pourimani *, Tayebeh Davoodmaghami Pages 192-199
    Introduction
    Nuclear radiation is potentially harmful to humans and soil contamination with radionuclides is the main source of human radiation exposure. These radionuclides can., enter to human body through the food chain. In this study, 34 soil samples were collected from between Arak city and Shazand Power Plant over 20 km length and analyzed.
    Materials And Methods
    The specific activities of 226Ra, 232Th, 40K, and 137Cs were measured in soil samples, using gamma-ray spectrometry and a high-purity germanium (HPGe) detector. For all the samples, we calculated radiological hazards such as radium equivalent (Raeq), dose rate in air (D), internal and external hazard indices (Hin, Hex), annual gonadal dose equivalent (AGDE), and excess lifetime cancer risk.
    Results
    The specific activities of 226Ra, 232Th, 40K, and 137Cs in the soil samples varied from 18.92 to 43.11, 25.31 to 54.27, 230.17 to 728.25, and from in and Hex wereless than unity. Excess lifetime cancer risk of the samples ranged from 0.21×10-3 to 0.31×10-3, which are close to the mean world value (0.29×10-3) butlower than the acceptable value (10-3).
    Conclusion
    The radiological parameters estimated from the specific activities of the radionuclides in soil were within the acceptable range, and therefore, radiation exposure poses no significant risks to the resident population in the vicinity of the power plant.
    Keywords: Dose Rate, Gamma Ray Spectrometry Radionuclides, Soil
  • Deepak Shrotriya *, Ram Shbad Yadav, R. N.L. Srivastava, Teerth Raj Verma Pages 200-205
    Introduction
    The present study is aimed to design and develop a tissue-equivalent pelvic phantom, mimicking the Indian female pelvic dimensions by means of locally available and cost-effective tissue substitutes having equivalent radiological properties.
    Materials And Methods
    For the purpose of the study, the real female pelvic bones were embedded for preparation. Paraffin wax, Aloe-vera powder, purified borax, and sodium benzoate, were used to obtain the proper density and effective atomic number. A hollow three-dimensional outer surface and the internal organs moulds were fabricated using gypsona bandage. The internal organs moulds were filled with semi-solid paraffin wax mixture, stabilized, and then embedded with pelvic bones and internal organs at the right anatomical positions. The surface mould, along with the bones and internal organs, were stabilized in their position in the final form, and verified with computed tomography (CT).
    Results
    The physical dimensions of the given female pelvic phantom were comparable with the mean dimensions of the Indian female pelvis. Furthermore this tissue-equivalent phantom was radiologically equivalent to the Indian human female pelvis in all respects. The CT numbers of the uterus, bladder, rectum, muscles, fats, bone, and cavities were 39.9, 30.5, 24.7, 34.6, -86.8, 578.6, and -220.9 HU, respectively. Furthermore, the relative electron densities of the muscle, fat and bones were 1.035, 0.913, and 0.779 in the phantom.
    Conclusion
    The dimensions and physico-radiological properties of the tissue substitutes provided a good inhomogeneous female pelvic phantom differing in dimensions with imported pelvic phantoms. Therefore, this phantom can be used for radiological dosimetric applications.
    Keywords: Phantom, Hounsfield Unit, Pelvis, Physico-Radiological Properties