فهرست مطالب

Medical Physics - Volume:12 Issue: 2, Spring 2015

Iranian Journal of Medical Physics
Volume:12 Issue: 2, Spring 2015

  • تاریخ انتشار: 1394/03/15
  • تعداد عناوین: 8
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  • Abdolkazem Ansarinejad, Anna Ferrari Pages 70-77
    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.
    Keywords: Hadron Therapy, Charged Particles, Simulation, Monte Carlo method
  • Mohammad Taghi Bahreyni Toossi, Eftekhar Rajab Bolookat, Raham Salek, Mohsen Layegh Pages 78-84
    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.
    Keywords: Nasopharyngeal Carcinoma, Radiotherapy, RANDO Phantom, Thermoluminescent Dosimetry
  • Mehrdad Gholami, Fataneh Nemati, Vahid Karami Pages 85-92
    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.
    Keywords: Quality Control, X-ray Output, kVp Accuracy
  • Esen Nsikan U., Obed, R. I. Pages 93-100
    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.
    Keywords: Entrance Skin Dose, diagnostic X-ray Examination, Akwa Ibom
  • Behrouz Rasuli, Ali Mahmoud- Pashazadeh, Mohammad Javad Tahmasebi Birgani, Mohammad Ghorbani, Mozafar Naserpour, Jafar Fatahi-Asl Pages 101-108
    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
    Thereproducibility 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.
    Keywords: Radiation Protection, Quality Control, Diagnostic X-ray, Radiography, Radiology Device
  • Sedigheh Sina, Fatemeh Lotfalizadeh, Mehrnoosh Karimipourfard, Neda Zaker, Bentolhoda Amanat, Mehdi Zehtabian, Ali. S. Meigooni Pages 109-120
    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.
    Keywords: Brachytherapy, Dosimetry, Phantom
  • Hassan Yousefnia, Samaneh Zolghadri, Amir Reza Jalilian Pages 121-128
    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.
    Keywords: Gallium, 67, Radiation Dose, Dosimetry
  • Mona Zolfaghari, Mahmood Sedaghatizadeh Pages 129-136
    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.
    Keywords: LINAC, BNCT, Fast Neutrons