Mashhad University of Medical SciencesIranian Journal of Medical Physics2345-36729120120301Evaluation of the Effects of Inhomogeneities on Dose Profiles Using Polymer Gel Dosimeter and Monte Carlo Simulation in Gamma Knife1832110.22038/ijmp.2012.321ENTayeb Allahverdi PourfallahBiochemistry and Biophysics Dept., Faculty of Medicine, Mazandaran University of Medical Sciences, Sari, IranMahmoud AllahverdiMedical Physics Dept., Faculty of Medicine, Tehran University of Medical Sciences, Tehran, IranMohammad Hasan ZahmatkeshNovin Medical Radiation Institute, Tehran, IranJournal Article20120115Introduction <br/>Polymer gel dosimeters offer a practical solution to 3D dose verification for conventional radiotherapy as well as intensity-modulated and stereotactic radiotherapy. In this study, EGSnrc calculated and PAGAT polymer gel dosimeter measured dose profiles from single shot irradiation with 18 mm collimator of Gamma Knife in homogeneous and inhomogeneous phantoms were compared with each other. <br/>Materials and Methods <br/>The head phantom was a custom-built 16 cm diameter plexiglas sphere. Inside the phantom, there were two cubic cutouts for inserting the gel vials and inhomogeneities. Following irradiation with the Gamma Knife unit, the polymer gel dosimeters were scanned with a 1.5 T MRI scanner. For the purpose of simulation the simplified channel of 60Co source of Gamma Knife BEAMnrc and for extracting the 3D dose distribution in the phantom, DOSXYZnrc codes were used. <br/>Results <br/>Within high isodose levels (>80%), there are dose differences higher than 7%, especially between air inserted and PTFE inserted phantoms, which were obtained using both simulation and experiment. This means that these values exceed the acceptance criterion of conformal radiotherapy and stereotactic radiosurgery (i.e., within some isodose levels, less than 93% of prescription dose are delivered to the target). <br/>Conclusion <br/>The discrepancies observed between the results obtained from heterogeneous and homogeneous phantoms suggest that Leksell Gamma Knife planning system (LGP) predictions which assume the target as a homogeneous material must be corrected in order to take care of the air- and bone-tissue inhomogeneities.Mashhad University of Medical SciencesIranian Journal of Medical Physics2345-36729120120301Introducing an Optimized Method for Obtaining X-ray Diffraction Patterns of Biological Tissues91732510.22038/ijmp.2012.325ENAli ChaparianMedical Physic Dept., Shahid Sadoughi University of Medical Sciences, Yazd, Iran0000-0003-2478-3014Mohammad Ali OghabianMedical Physic Dept., Tehran University of Medical Sciences, Tehran, IranVahid ChangiziRadiology Technology Dept., Tehran University of Medical Sciences, Tehran, IranJournal Article20120116Introduction <br/>Individual X-Ray diffraction patterns of biological tissues are obtained via interference of coherent scattering with their electrons. Many scientists have distinguished normal and cancerous breast tissue, bone density, and urinary stone types using the X-Ray diffraction patterns resulting from coherent scattering. The goal of this study was to introduce an optimized method for obtaining X-ray diffraction patterns of different types from biological tissues. <br/>Materials and Methods <br/>A special tool constituting primary and scatter collimators as well as a sample holder was designed and built. All measurements were done using an X-ray tube, the above-mentioned tool, and a semiconductor detector (HPGe). The X-ray diffraction patterns of some tissue-equivalent materials (acrylic, polyethylene, nylon, and calcium carbonate) and biological tissues (adipose, muscle, and bone) were obtained. <br/>Results <br/>The corresponding peak positions for adipose, muscle, bone, acrylic, polyethylene, nylon, and calcium carbonate in corresponding X-ray diffraction patterns are located in 1.1±0.055 nm<sup>-1</sup>, 1.41±0.072, 1.6±0.08 nm<sup>-1</sup>, 0.8±0.04 nm<sup>-1</sup>, 1.03±0.051 nm<sup>-1</sup>, 1.22±0.061 nm<sup>-1</sup>, and 1.7 ± 0.085 nm<sup>-1</sup>, respectively. <br/>Conclusion <br/>The X-ray diffraction patterns obtained in this study were in good agreement relative to previous measurements in terms of peak position. This study introduces a useful setup for extraction of X-ray diffraction patterns from different biological tissues.Mashhad University of Medical SciencesIranian Journal of Medical Physics2345-36729120120301Applicator Attenuation Effect on Dose Calculations of Esophageal High-Dose Rate Brachytherapy Using EDR2 Film192432610.22038/ijmp.2012.326ENSeyed Mohsen Hosseini DaghighRadiation Medicine Department, Shahid Beheshti University, Tehran, IranSeied Rabi MahdaviMedical Physics Department, Tehran University of Medical Science, Tehran, IranSeyed Mahmoud AghamiriRadiation Medicine Department, Shahid Beheshti University, Tehran, IranRamin JaberiImam Khomeini Hospital, Tehran University of Medical Science, Tehran, IranHamid Reza BaghaniRadiation Medicine Department, Shahid Beheshti University, Tehran, IranRamezan EidiRadiation Medicine Department, Shahid Beheshti University, Tehran, IranElham BoroghaniPhysics Department, Gilan University, Rasht, IranJournal Article20110827Introduction <br/>Interaluminal brachytherapy is one of the important methods of esophageal cancer treatment. The effect of applicator attenuation is not considered in dose calculation method released by AAPM-TG43. In this study, the effect of High-Dose Rate (HDR) brachytherapy esophageal applicator on dose distribution was surveyed in HDR brachytherapy. <br/>Materials and Methods <br/>A cylindrical PMMA phantom was built in order to be inserted by various sizes of esophageal applicators. EDR2 films were placed at 33 mm from Ir-192 source and irradiated with 1.5 Gy after planning using treatment planning system for all applicators. <br/>Results <br/>The results of film dosimetry in reference point for 6, 8, 10, and 20 mm applicators were 1.54, 1.53, 1.48, and 1.50 Gy, respectively. The difference between practical and treatment planning system results was 0.023 Gy (<2.7%), on average. <br/>Conclusion <br/>Due to the similar practical results for different esophageal applicators, it can be concluded that attenuation properties of applicator wall doesn't have a significant difference with water and therefore the Flexiplan treatment planning system accuracy is further confirmed.Mashhad University of Medical SciencesIranian Journal of Medical Physics2345-36729120120301Repeatability of Detecting Visual Cortex Activity in Functional Magnetic Resonance Imaging253232710.22038/ijmp.2012.327ENMahboubeh Ma'soumbeigiMedical Physics Department, Tehran University of Medical Sciences, Tehran, IranAli MirzajaniOptometry Department, Rehabilitation Faculty, Tehran University of Medical Sciences, Tehran, Iran.
Medical Physics Department, Tehran University of Medical Sciences, Tehran, IranJournal Article20111218Introduction <br/>As functional magnetic resonance imaging (fMRI) is too expensive and time consuming, its frequent implementation is difficult. The aim of this study is to evaluate repeatability of detecting visual cortex activity in fMRI. <br/>Materials and Methods <br/>In this study, 15 normal volunteers (10 female, 5 male; Mean age±SD: 24.7±3.8 years) attended. Functional magnetic resonance images were obtained during a visual task of sine-wave with spatial frequency of 1.84 cpd and temporal frequency of 8 Hz in three scan runs. Two runs of functional images were provided consecutively in a session, and the third run was provided 1-6 weeks later. The activation map was created using the data obtained from the block-designed fMRI study. Voxels whose Z value was above a threshold of 2.3, at a significance level p=0.05, were considered activated. After image processing, the blood oxygen level dependent (BOLD) signal changes and the number of activated voxels in response to visual stimuli were compared in different runs. <br/>Results <br/>The results of this study demonstrate no significant difference between the number of activated voxels and BOLD signal in first and second runs in one session (Paired t-test, p>0.05). Moreover, there is a considerable correlation between first and second scan runs (rsignal=0.74, p=0.006 and rvoxel=0.62, p=0.03), while the correlation between the runs in separate sessions is weak (rsignal=0.28, p=0.38 and rvoxel=0.32, p=0.31). <br/>Conclusion <br/>Since the repeatability of BOLD signal and number of activated voxels in one session is considerably better than that in the separate sessions, it is suggested that in fMRI visual studies that need repeated scanning, scans should be acquired during a single session.Mashhad University of Medical SciencesIranian Journal of Medical Physics2345-36729120120301Developing a Verification and Training Phantom for Gynecological Brachytherapy System334032810.22038/ijmp.2012.328ENMahbobeh NazarnejadScience and Research Branch, Islamic Azad University, Tehran, IranSeied Rabi MahdaviDepartment of Medical physics, Tehran University of Medical Sciences, Tehran, IranKhadijeh AsnaashariSchool of allied medicine, Tehran University of Medical Sciences, Tehran, IranMahdi SadeghiScience and Research Branch, Islamic Azad University, Tehran, IranAlireza NikoofarDepartment of Medical physics, Tehran University of Medical Sciences, Tehran, IranJournal Article20111119Introduction <br/>Dosimetric accuracy is a major issue in the quality assurance (QA) program for treatment planning systems (TPS). An important contribution to this process has been a proper dosimetry method to guarantee the accuracy of delivered dose to the tumor. In brachytherapy (BT) of gynecological (Gyn) cancer it is usual to insert a combination of tandem and ovoid applicators with a complicated geometry which makes their dosimetry verification difficult and important. Therefore, evaluation and verification of dose distribution is necessary for accurate dose delivery to the patients. <br/>Materials and Methods <br/>The solid phantom was made from Perspex slabs as a tool for intracavitary brachytherapy dosimetric QA. Film dosimetry (EDR2) was done for a combination of ovoid and tandem applicators introduced by Flexitron brachytherapy system. Treatment planning was also done with Flexiplan 3D-TPS to irradiate films sandwiched between phantom slabs. Isodose curves obtained from treatment planning system and the films were compared with each other in 2D and 3D manners. <br/>Results <br/>The brachytherapy solid phantom was constructed with slabs. It was possible to insert tandems and ovoids loaded with radioactive source of Ir-192 subsequently. Relative error was 3-8.6% and average relative error was 5.08% in comparison with the films and TPS isodose curves. <br/>Conclusion <br/>Our results showed that the difference between TPS and the measurements is well within the acceptable boundaries and below the action level according to AAPM TG.45. Our findings showed that this phantom after minor corrections can be used as a method of choice for inter-comparison analysis of TPS and to fill the existing gap for accurate QA program in intracavitary brachytherapy. The constructed phantom also showed that it can be a valuable tool for verification of accurate dose delivery to the patients as well as training for brachytherapy residents and physics students. Mashhad University of Medical SciencesIranian Journal of Medical Physics2345-36729120120301Evaluation of Sonochemiluminescence in a Phantom in the Presence of Protoporphyrin IX Conjugated to Nanoparticles415032910.22038/ijmp.2012.329ENAhmad ShaneiMedical Physics and Medical Engineering Dept., Isfahan University of Medical Sciences, Isfahan, IranAmeneh SazgarniaMedical Physics Dept., Research Centre and Department of Medical Physics, Mashhad University of Medical Sciences, Mashhad, Iran0000-0000-0000-0000Mohammad Hassanzadeh-KayyatPharmaceutics Dept., Pharmaceutical Research Center, Mashhad University of Medical Sciences, Mashhad, IranHossein EshghiChemistry Dept., Ferdowsi University of Mashhad, Mashhad, IranSamaneh SoudmandResearch Center of Medical Physics, Mashhad University of Medical Sciences, Mashhad, IranNeda Attaran KakhkiChemistry Dept., Ferdowsi University of Mashhad, Mashhad, IranJournal Article20111123Introduction <br/>When a liquid is irradiated with high-intensity and low-frequency ultrasound, acoustic cavitation occurs and there are some methods to determine and quantify this phenomenon. The existing methods for performing these experiments include sonochemiluminescence (SCL) and chemical dosimetric methods. The particles in a liquid decrease the ultrasonic intensity threshold needed for cavitation onset. In this study, a new nanoconjugate made up of Protoporphyrin IX (PpIX) and gold nanoparticles (GNP), i.e., Au-PpIX was used to provide nucleation sites for cavitation. The nonradiative relaxation time of PpIX in the presence of GNPs is longer than the similar time for PpIX without GNPs. This effect can be used in medical diagnostic and therapeutic applications. <br/>Materials and Methods <br/>The acoustic cavitation activity was investigated studying integrated SCL signal in the wavelength range of 400-500 nm in polyacrylamide gel phantom containing luminol using a cooled CCD spectrometer at different intensities of 1 MHz ultrasound. In order to confirm these results, a chemical dosimetric method was utilized, too. <br/>Results <br/>SCL signal level in gel phantom containing Au-PpIX was higher than the other phantoms. These results have been confirmed by the chemical dosimetric data. <br/>Conclusion <br/>This finding can be related to the existence of PpIX as a sensitizer and GNPs as cavitation nuclei. In other words, nanoparticles have acted as the sites for cavitation and have increased the cavitation rate. Another theory is that activation of PpIX has produced more free radicals and has enhanced the SCL signal level.Mashhad University of Medical SciencesIranian Journal of Medical Physics2345-36729120120301A New Method for Detection of Backscattered Signals from Breast Cancer Tumors: Hypothesis Testing Using an Adaptive Entropy-Based Decision Function516433010.22038/ijmp.2012.330ENSeyed Vahab ShojaediniIranian Research Organization for Science and Technology, Tehran, IranRahman KabiriCommunication Engineering Department, Tehran University, Tehran, IranJournal Article20120123Introduction <br/>In recent years methods based on radio frequency waves have been used for detecting breast cancer. Using theses waves leads to better results in early detection of breast cancer comparing with conventional mammography which has been used during several years. <br/>Materials and Methods <br/>In this paper, a new method is introduced for detection of backscattered signals which are received by microwave breast radar. In this method, a decision function is constructed based on noise and signal cross-entropy, using hypothesis testing concept. Then noise and signal are separated using the calculated value for the decision function in each time frame. To estimate value of the decision function, discrete wavelet transform and discrete S transform are used. <br/>Results <br/>Performance of the proposed method was evaluated in two different scenarios, in which the breast was considered homogenous and heterogeneous, respectively. The obtained results showed that the proposed method detected breast backscattered signals 55% and 49% better than existing methods in two above scenarios. <br/>Conclusion <br/>Performance of S transform was 21% better than discrete wavelet transform in detection of weak backscattered signals. So it can be concluded that hypothesis testing method which uses S coefficients of received wave for construction of its decision function may be a suitable choice for detection of backscattered signals in breast radar.Mashhad University of Medical SciencesIranian Journal of Medical Physics2345-36729120120301A Comparison of the Dosimetric Parameters of Cs-137 Brachytherapy Source in Different Tissues with Water Using Monte Carlo Simulation657433110.22038/ijmp.2012.331ENSedigheh SinaSchool of Mechanical Engineering, Nuclear Engineering Department, Shiraz University, Shiraz, IranReza FaghihiSchool of Mechanical Engineering, Nuclear Engineering Department, Shiraz University, Shiraz, Iran
Radiation Research Center, Shiraz University, Shiraz, Iran0000000332386887Ali Soleymani MeigooniComprehensive Cancer Center of Nevada, 3730 S. Eastern Ave., Las Vegas, Nevada, USAJournal Article20120119Introduction <br/>After the publication of Task Group number 43 dose calculation formalism by the American Association of Physicists in Medicine (AAPM), this method has been known as the most common dose calculation method in brachytherapy treatment planning. In this formalism, the water phantom is introduced as the reference dosimetry phantom, while the attenuation coefficient of the sources in the water phantom is different from that of different tissues. The purpose of this study is to investigate the effects of the phantom materials on the TG-43 dosimetery parameters of the Cs-137 brachytherapy source using MCNP4C Monte Carlo code. <br/>Materials and Methods <br/>In this research, the Cs-137 (Model Selectron) brachytherapy source was simulated in different phantoms (bone, soft tissue, muscle, fat, and the inhomogeneous phantoms of water/bone) of volume 27000 cm3 using MCNP4C Monte Carlo code. *F8 tally was used to obtain the dose in a fine cubical lattice. Then the TG-43 dosimetry parameters of the brachytherapy source were obtained in water phantom and compared with those of different phantoms. <br/>Results <br/>The percentage difference between the radial dose function g(r) of bone and the g(r) of water phantom, at a distance of 10 cm from the source center is 20%, while such differences are 1.7%, 1.6% and 1.1% for soft tissue, muscle, and fat, respectively. The largest difference of the dose rate constant of phantoms with those of water is 4.52% for the bone phantom, while the differences for soft tissue, muscle, and fat are 1.18%, 1.27%, and 0.18%, respectively. The 2D anisotropy function of the Cs-137 source for different tissues is identical to that of water. <br/>Conclusion <br/>The results of the simulations have shown that dose calculation in water phantom would introduce errors in the dose calculation around brachytherapy sources. Therefore, it is suggested that the correction factors of different tissues be applied after dose calculation in water phantoms, in order to decrease the errors of brachytherapy treatment planning. <br/>