فهرست مطالب

Medical Physics - Volume:12 Issue: 4, 2016
  • Volume:12 Issue: 4, 2016
  • تاریخ انتشار: 1395/02/01
  • تعداد عناوین: 8
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  • Mohammad Amin Mosleh, Shirazi, Saeed Rahimi, Sareh Karbasi Pages 230-234
    Introduction
    In this study, we aimed to assess the medium-term energy stability of a 6MV Elekta CompactTM linear accelerator. To the best of our knowledge, this is the first published article to evaluate this linear accelerator in terms of energy stability. As well as investigating the stability of the linear accelerator energy over a period of several weeks, the results will be useful for estimation of the required tolerance values for the beam quality factor (BQF) of the PTW QUICKCHECK weblineTM (QCW) daily checking device.
    Materials And Methods
    Over a 13 week period of routine clinical service, 52 daily readings of BQF were taken and then analyzed for a 10×10 cm2 field.
    Results
    No decreasing or increasing trend in BQF was observed over the study period. The mean BQF value was estimated at 5.4483 with a standard deviation (SD) of 0.0459 (0.8%). The mean value was only 0.1% different from the baseline value.
    Conclusion
    The results of this medium-term stability study of the Elekta Compact linear accelerator energy showed that 96.2% of the observed BQF values were within ±1.3% of the baseline value. This can be considered to be within the recommended tolerance for linear accelerator photon beam energy. If an approach of applying ±3 SD is taken, the tolerance level for BQF may be suggested to be set at ±2.5%. However, further research is required to establish a relationship between BQF value and the actual changes in beam energy and penetrative quality.
    Keywords: Radiotherapy, Linear accelerator, Quality control, Photons, Beam, Energy
  • Mohammad Hasan Akhavan Karbasi, Hassan Zarghani, Seyed Ali Akhavan, Nastaran Donyadide, Pejman Shamshiry Pages 235-241
    Introduction
    Xerostomia is one of side-effects of radiotherapy for head and neck cancers. No definitive method has been proposed for the treatment of this condition. However, pilocarpine is considered effective for the management of chronic xerostomia. The purpose of the present study was to assess the preventive effect of pilocarpine.
    Materials And Methods
    This study was performed on 34 patients with head and neck cancers, undergoing radiation therapy (5000 cGy). The patients were randomly divided into two groups. The case group was administered 16 drops of pilocarpine (2%) eye drops per day, while the control group received normal saline; the treatment plan continued for four weeks. Unstimulated whole saliva flow rate was measured at four stages: two weeks before radiotherapy (baseline), the first day of radiotherapy, and two and four weeks after the initiation of radiotherapy.
    Results
    At baseline and the first day of radiotherapy, no significant differences were observed in the amount of saliva between the case and control groups (P
    Conclusion
    According to the findings, pilocarpine was found to be effective for the prevention of xerostomia. Moreover, it could restrain the decline in the amount of saliva and reduce the rate of xerostomia.
    Keywords: Head, Neck Neoplasms, Pilocarpine, Radiotherapy, Saliva, Xerostomia
  • Amir Hakimi, Amir Reza Jalilian, Ali Ghanbarzadeh, Hamed Rezaee Jam Pages 242-250
    Introduction
    Compartmental analysis allows the mathematical separation of tissues and organs to determine activity concentration in each point of interest. Biodistribution studies on humans are costly and complicated, whereas such assessments can be easily performed on rodents.
    In this study, we aimed to develop a pharmacokinetic model of 153Sm-maltolate complex as a novel therapeutic agent and free 153Sm cation in normal rats using compartmental analysis to evaluate the behavior of this complex.
    Materials And Methods
    We developed a physiologically-based pharmacokinetic model for scaling up the activity concentration in each organ with respect to time. In the mathematical model, physiological parameters including organ volume, blood flow rate, and vascular permeability were used. The compartments (organs) were connected anatomically, which allowed the use of scale-up techniques to predict new complex distribution in each body organ.
    Results
    The concentration of 153Sm-maltolate complex and free 153Sm cation in various organs was measured at different time intervals. The time-dependent behavior of the biodistribution of these two radiotracers was modeled, using compartmental analysis; the detected behaviors were drawn as a function of time.
    Conclusion
    The variation in radiopharmaceutical concentration in organs of interest could be described by summing seven to nine exponential terms, which approximated the experimental data with a precision of > 1% in comparison with the original data from animal studies.
    Keywords: Biodistribution, Modeling, Compartmental Analysis, Samarium, 153, Maltolate
  • Hadi Kalani, Alireza Akbarzadeh, Sahar Moghimi Pages 251-261
    Introduction
    we aimed to introduce a 6-universal-prismatic-spherical (UPS) parallel mechanism for the human jaw motion and theoretically evaluate its kinematic problem. We proposed a strategy to provide a fast and accurate solution to the kinematic problem. The proposed strategy could accelerate the process of solution-finding for the direct kinematic problem by reducing the number of required iterations in order to reach the desired accuracy level.
    Materials And Methods
    To overcome the direct kinematic problem, an artificial neural network and third-order Newton-Raphson algorithm were combined to provide an improved hybrid method. In this method, approximate solution was presented for the direct kinematic problem by the neural network. This solution could be considered as the initial guess for the third-order Newton-Raphson algorithm to provide an answer with the desired level of accuracy.
    Results
    The results showed that the proposed combination could help find a approximate solution and reduce the execution time for the direct kinematic problem, The results showed that muscular actuations showed periodic behaviors, and the maximum length variation of temporalis muscle was larger than that of masseter and pterygoid muscles. By reducing the processing time for solving the direct kinematic problem, more time could be devoted to control calculations.. In this method, for relatively high levels of accuracy, the number of iterations and computational time decreased by 90% and 34%, respectively, compared to the conventional Newton method.
    Conclusion
    The present analysis could allow researchers to characterize and study the mastication process by specifying different chewing patterns (e.g., muscle displacements).
    Keywords: Kinematic Problem, Mastication Robot, Neural Networks, Newton, Raphson Method
  • Alireza Mohammadkarim, Hasan Ali Nedaie, Mahmoud Allahverdi, Mahbod Esfehani, Alireza Shirazi, Ghazale Geraily Pages 262-270
    Introduction
    Evaluation of the delivered dose of externally wedged photon beams by external diode dosimeters during the treatment process requires the estimation of exit surface dose correction factors in various wedge angles and field sizes.
    Materials And Methods
    A system of absorbed dose evaluation, using p-type diode dosimeters placed on the exit surface of a phantom, was characterized for externally wedged photons with the maximum square field size. The values of wedge correction factor on the exit surface of the polystyrene phantom were determined for 60Co and 6 MV photons. Then, the wedge correction factors were estimated at desirable depths.
    Results
    Based on the findings, the deviation of off-axis wedge correction factors of the exit surface wedged fields from the central axis factor may be as large as ±10% at the evaluated depths. The results showed that the absorbed dose at each depth of patient tissue could be estimated by applying an accurate exit wedge correction factor for that particular depth, with negligible probable errors (below 1.5%).
    Conclusion
    In case positioning a diode dosimeter on the patient’s entrance surface of a phantom of patients is troublesome, the diode dosimeter can be placed on the exit surface in order to evaluate the absorbed dose for externally wedged photons. Based on the findings, exit dose correction factors for wedged beams cannot be discarded; in fact, these factors are variable at different directions of externally wedged beams.
    Keywords: Absorbed Dose, Diode Dosimeter, Wedge, Field Size, Radiation Therapy
  • Zahra Poursharif, Ali Ebrahiminia, Mohsen Asadinezhad, Abolfazl Nickfarjam, Abolghasem Haeri, Karim Khoshgard Pages 271-277
    Introduction
    Foodstuffs are known to contain natural and artificial radionuclides. Determination of radionuclide concentration is of great significance for the protection of human health. The main objective of the present study was the quantification of radionuclides in tea samples, cultivated in Guilan Province in North of Iran.
    Materials And Methods
    The activity concentrations of 226Ra, 232Th, 40K, and 137Cs in 18 tea samples were measured, using a gamma spectrometry system. In addition, radium equivalent index (Raeq) and radiation hazard index (HI) were calculated. ANOVA test was used for the statistical analysis of the data
    Results
    The concentration of 137Cs was below the minimum detectable activity (MDA). The concentrations of 226Ra and 232Th ranged from
    Conclusion
    According to the findings, the activity level of radionuclides in tea samples was found to be within the acceptable range and therefore, non-threatening to public health.
    Keywords: Radionuclide, Tea, Gamma Spectrometry
  • Fatemeh Razghandi, Reza Izadi, Ali Mowlavi Pages 278-283
    Introduction
    One of the important applications of nuclear physics in medicine is the use of radioactive elements as radiopharmaceuticals. Metastatic bone disease is the most common form of malignant bone tumors. Samarium-153-ethylene diamine tetramethylene phosphonate (153Sm-EDTMP) as a radiopharmaceutical is used for pain palliation. This radiopharmaceutical usually emits beta particles, which have a high uptake in bone tissues. The purpose of this study was to calculate the radiation dose distribution of 153Sm-EDTMP in bone and other tissues, using MCNPX Monte Carlo code in the particle transport model.
    Materials And Methods
    Dose delivery to the bone was simulated by seeking radiopharmaceuticals on the bone surface. The phantom model had a simple cylindrical geometry and included bone, bone marrow, and soft tissue.
    Results
    The simulation results showed that a significant amount of radiation dose was delivered to the bone by the use of this radiopharmaceutical.
    Conclusion
    Thebone acted as a fine protective shield against rays for the bone marrow. Therefore, the trivial absorbed dose by the bone marrow caused less damage to bone-making cells. Also, the high absorbed dose of the bone could destroy cancer cells and relieve the pain in the bone.
    Keywords: Dose Distribution, MCNPX Code, 153Sm, EDTMP
  • Hasan Zarghani, Mohammad Taghi Bahreyni Toossi Pages 284-291
    Introduction
    The purpose of this study was to estimate organ and effective doses in patients undergoing some common X-ray examinations in Sabzevar, Iran. The effective dose is one of the best parameters for describing the amount of radiation dose received by a patient undergoing any diagnostic X-ray examination. The public dose from X-ray examinations depends on various factors, and its contribution to the overall public dose from medical applications widely varies in different societies; however, in Iran, limited data is available on this subject.
    Materials And Methods
    In the present study, we aimed to estimate organ and effective doses arising from some common X-ray examinations on patients. Organ and effective doses were calculated by employing PCXMC program, based on Monte Carlo method.
    Results
    The mean effective doses in this study were compared with similar findings reported in previous research. The applied methods in different studies are the main factors, which influence the effective dose values.
    Conclusion
    Radiation doses to radiosensitive organs such as the ovaries, testicles, and thyroid may induce harmful effects, e.g., cancer and genetic effects. Therefore, we should try to maintain the organ doses as low as possible.
    Keywords: Effective dose, Organ dose, PCXMC program, Radiography, Radiation Effects