IRANIAN JOURNAL OF MEDICAL PHYSICS
Year:2013 | Volume:10 | Issue:3|Papers Count:8

IntroductionThe use of cut-outs in electron applicators make changes on output, isodose, and percentage depth dose (PDD) curves. These changes and electron beam dose distribution in the form of three-dimensional (3D) can be measured by gel dosimeters.Materials and MethodsDosimetry was performed with and without a square shield (6×6 cm2 field). The energies were 4, 9, and 16 MeV and phantom was filled with MAGIC gel polymer. For each section, transverse relaxation rate (R2) maps were obtained from MRI images and percentage depth doses and isodose curves were plotted.ResultsAverage energy was 3.029 MeV for the energy of 4 MeV and 8.155 MeV for the energy of 9 MeV. Surface dose was higher in shielded field compared with the open one (due to electron scattering between the phantom and lead) which increased with increasing of energy. In the open field, for energies equal to 4, 9, and 16 MeV, the surface dose was 6.40, 6.48, and 7.20 Gy and for the shielded mode, they were 6.63, 7.04, and 7.31 Gy, respectively. Also error values showed less errors and higher accuracy on curves by increasing of energy.ConclusionInvestigation of an isodose pattern in the shielded mode showed scattering due to the lead, which is on the applicator. Overall, the results of this study demonstrated the value and potential of this dosimetric method with respect to characteristics such as stability, responsiveness and specially ability to show three dimensional electron beam dose distribution.

IntroductionThe increasing practice of interventional fluoroscopy in diagnosis and treatment of cardiovascular disease has risen attention to improve radiation protection of patients and cardiologists in these relatively high dose techniques. Therefore, nowadays there is an emphasis on the measurement of radiation dose received by patients and cardiologists arising from the relevant procedures.Materials and MethodsMaximum skin dose of 90 patients in two hospitals in Mashhad have been measured by a grid of 30 thermo luminescent dosimeters (TLDs). The X-ray units were Axiom Artis Siemens in both hospitals which were equipped with integrated dose area product (DAP) meters. The procedures were divided into two groups: diagnostic procedures (angiography and angiography with measurement of left or right ventricle and pulmonary artery) and therapeutic procedures (angioplasty with or without dilatation or stent and angiography with angioplasty). DAP value, fluoro time, and cumulative dose at Interventional Reference Point (CDIRP) were also registered for each procedure.ResultsThe mean values of maximum skin dose (MSD) and DAP for diagnostic procedures were 68.51 mGy and 20.96 Gy.cm2, respectively and for therapeutic procedures 344.18 mGy and 70.94 Gy.cm2, respectively. A good correlation was found between MSD and DAP (R=0.88) but correlation between MSD and CDIRP was stronger (R=0.90).ConclusionMSD values did not exceed the 2000 mGy dose threshold for deterministic effects. The highest MSD obtained for diagnostic procedures was 229.40 mGy and for therapeutic procedures it was 820.50 mGy. The results show that CDIRP can be a fairly good estimate of MSD.

IntroductionThe diagnosis and separation of cancerous tumors in medical images require accuracy, experience, and time, and it has always posed itself as a major challenge to the radiologists and physicians.Materials and MethodsWe Received 290 medical images composed of 120 mammographic images, LJPEG format, scanned in grayscale with 50 microns size, 110 MRI images including of T1-Wighted, T2-Wighted, and Proton Density (PD) images with 1-mm slice thickness, 3% noise and 20% intensity non-uniformity (INU) as well as 60 lung cancer images acquired using the 3D CT scanner, GE Medical System Light Speed QX/i helical, yielding 16-bit slices taken from various medical databases. By applying the Discrete Wavelet Transform (DWT) on the input images and constructing the approximate coefficients of scaling components, the different parts of image were classified. In next step using k-means algorithm, the appropriate threshold was selected and finally the suspicious cancerous mass was separated by implementation image processing techniques.ResultsBy implementing the proposed algorithm, acceptable levels of accuracy 92.06%, sensitivity 89.42%, and specificity 93.54% were resulted for separating the target area from the rest of image. The Kappa coefficient was approximately 0.82 which illustrate suitable reliability for system performance. The correlation coefficient of physician’s early detection with our system was highly significant (p<0.05).ConclusionThe precise positioning of the cancerous tumor enables the radiologists to determine the progress level of the disease. The low Positive Predictive Value (PPV) and high Negative Predictive Value (NPV) of the system is a warranty of the system and both clinical specialist and patients can trust the software and output.

IntroductionLow dose rate brachytherapy sources have been widely used for interstitial implants in tumor sites, particularly in prostate. Dosimetric characteristics of a new IrSeed 125I brachytherapy source have been determined using the LiF thermo luminescent dosimeter (TLD) chips.Materials and MethodsDose rate constant, radial dose function, and anisotropy function around the IrSeed 125I source were measured in a plexiglass phantom using TLD-100 chips. A plexiglass slab phantom with dimensions of 30´30´7.3 cm3 was used to measure dose distribution around the source.ResultsDose rate constant was measured to be equal to 0.965±0.006 cGyh-1U-1. Radial dose function, anisotropy function, and geometry function have been presented as tabulated data for the IrSeed source. ConclusionBasically, the dosimetric parameters presented here for this new IrSeed source have clinical and treatment planning applications.

ntroductionThis paper proposes the concept of autonomous drug-encapsulated nanoparticle (ADENP) as a novel noninvasive approach to prevent atherosclerosis. ADENP consists of three simple units of sensor, controller (computing), and actuator. The hardware complexity of ADENP is much lower than most of the nanorobots, while the performance is maintained by the synergism in the swarm architecture.Materials and MethodsSince high accumulation of low density lipoprotein (LDL) macromolecules within the arterial wall plays a critical role in the initiation and development of atherosclerotic plaques, the task of the swarm of ADENPs is autonomous feedback control of LDL level in the interior of the arterial wall. In this study, we consider two specific types of ADENPs with distinguishing capabilities. The performance of each type is evaluated and compared on a well-known mathematical model of the arterial wall through computer simulation.ResultsSimulation results demonstrate that the proposed approach can successfully reduce the LDL level to a desired value in the arterial wall of a patient with very high LDL level that is corresponding to the highest rates of cardiovascular disease events. Moreover, it is shown that ADENP is capable of distinguishing between healthy and unhealthy arterial walls to reduce the drug side effects.ConclusionThe proposed approach is a promising autonomous non-invasive method to prevent and treat complex diseases such as atherosclerosis.

IntroductionRelative dose computation is a necessary step in radiation treatment planning. Therefore, finding an approach that is both fast and accurate seems to be necessary. The purpose of this work was to investigate the feasibility of natural cubic spline to reconstruct dose maps for linear accelerator radiation treatment fields in comparison with those of the simulation.Materials and MethodsA natural cubic spline algorithm was used to reproduce dose calculations of linac radiation treatment fields resulting from GEANT4 application for tomographic emission (GATE) simulation. The spline algorithm was used to compute percent depth dose of radiation therapy fields for 6 MV X-rays, which were calculated by simulation of Elekta Compact Linac. It reconstructed 2-dimensional dose maps and created isodose distributions. This dose maps were evaluated and compared with the simulation, where the g -index was used.ResultsA good agreement was found between the doses calculated from the simulation and the spline. In particular, an average g-index passing rate of 0.24 was obtained for sample percent depth dose distributions, and an average g -index passing rate of 0.20 was observed for sample dose profiles.ConclusionNatural cubic spline has been established to calculate dose maps from field characteristics. The feasibility and possibility of natural cubic spline to calculate dose maps for linac radiation therapy fields in a homogeneous phantom has been demonstrated.

IntroductionIn CT imaging, metallic implants inside the tissues cause metal artifact that reduce the quality of image for diagnosis. In order to reduce the effect of this artifact, a new method with more appropriate results has been presented in this research work.Materials and MethodsThe presented method comprised of following steps: a) image enhancement and metal areas extraction, b) sinogram transform of original image, c) metal segments and metal traces inside the sinogram transform of original image segmented by using Fuzzy C means, d) interpolation of metal traces inside the original image sinogram and filtering, and e) adding the image of metal parts to the filtered image to obtain the corrected image.ResultsFifty CT scan images from Alzahra Hospital in Isfahan were used to evaluate the proposed method. The proposed method was applied to images which had implants in regions such as femur, hip, tooth, brain, and stomach. The results showed an intensively reduced in metal artifact and quality improvement of images till 90% for accuracy, compared with the radiologist report.ConclusionThe proposed method reduced the effect of metal artifact by maintaining the specification of other tissues. Furthermore, the consumed time to process the suggested algorithm in this study was less than conventional methods. For instance, the consumed time for CT image, including a metal in the femur region was about 20% of the conventional method.

IntroductionFor dose measurement in Megavoltage (MV) photon beams with ion chambers, the effect of volume occupied by the air cavity is not negligible. Therefore, the result of measurement should be corrected with a displacement perturbation correction factor (Pdis) or using an effective point of measurement (EPOM). The aim of this study is to calculate the EPOM for cylindrical ion chamber and to evaluate the fixed EPOM that was recommended by standard dosimetry protocols.Materials and MethodsPercent depth doses (PDDs) for 6 MV and 18 MV were measured with two types of chambers for different depths and field sizes. The EPOM was calculated using results obtained from measurement data for two types of chambers, comparison of the readings, and using dosimetry, mathematical, and statistical consideration. For displacement correction factor Dr=0, Dr=0.6r and different Dr, the minimum standard deviations ratio (SDRs) were calculated at several depths and field sizes.ResultsMaximum level of SDRs was about 0.38% and 0.49% (when assuming variable Dr) for 6 MV and 18 MV, respectively (which was less than 0.5% and acceptable). This quantity was greater than one (for assuming = 0.6r) and greater than 2 when there was no shift (Dr =0)ConclusionThe results show that the recommended shift for cylindrical ion chamber in dosimetry protocols (upstream of 0.6r) is not correct and using a fixed value for the EPOM at all photon beam energies, depths, and field sizes is not suitable for accurate dosimetry.