فهرست مطالب
Iranian Journal of Medical Physics
Volume:18 Issue: 5, Sep-Oct 2021
- تاریخ انتشار: 1400/07/22
- تعداد عناوین: 11
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Pages 300-305IntroductionDetecting scattered photons in the photo peak window degrades the image contrast and quantitative accuracy of single-photon emission computed tomography (SPECT) imaging. This study aimed to determine optimal main- and sub-energy windows for Triple Energy Window (TEW) in In-111.Material and MethodsWe used the simulating medical imaging nuclear detectors (SIMIND) program to simulate the Siemens SYMBIA gamma camera equipped with a medium energy (ME) collimator. We also used the SIMIND Monte Carlo program to generate theIn-111SPECT projection data of the Jaszczak phantom. The phantom consisting of six spheres with different diameters (9.5, 12.7, 19.1, 15.9, 25.4, and 31.8 mm) was used to evaluate the image contrast. Geometric, scatter, and penetration fraction, point spread functions, and contrast curves were drawn and compared.ResultsThe results showed that the 171keVphotopeak compared to the 245keVphotopeak yielded the best results with an ME collimator when the TEW scatter correction method was applied. The reason can be the large amount of scatter and penetration from the photo peak and the collimator for the 245keVphotopeak window.ConclusionWith the TEW scatter correction method, it is better to use a 171keVphotopeak window because of its better spatial resolution and image contrast.Keywords: SPECT Contrast In, 111 SIMIND Program
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Pages 306-313Introduction
The present study investigated the correlations between the patient’s dose-area product (DAP) values and cardiologist’s dose using Monte Carlo simulation. During angiography procedures, patients are exposed to the primary beam; however, the cardiologist is irradiated by the scattered radiation arising from the table and the surrounding equipment. Accordingly, the cardiologist’s dose is directly related to the patient’s dose.
Material and MethodsThis study investigated 25 cardiac angiography procedures. In each procedure, the DAP readings and the cardiologist dose as measured using an electronic personal dosimeter placed over the apron were recorded. Moreover, the DAP values and dose received by the cardiologist in the chest region were calculated using the Monte Carlo N-Particle extended code. For the validation of the simulated spectrum, dosimetric measurements were made using a Farmer ionization chamber and a phantom.
ResultsThe data obtained from 18 simulations showed that there was a strong linear relationship (R2=0.71) between the two variables of cardiologist’s dose and patient’s DAP. Likewise, the obtained results of dosimetry conducted on the patients in 25 cardiac angiography procedures revealed that there was a strong relationship (R2=0.78) between the two variables.
ConclusionThe reported correlation rates show the appropriateness of the physician radiation exposure to total patient’s DAP. With respect to the strong correlation coefficient obtained from the simulation method, it is recommended that this method should be verified by dosimetry. The findings of this study showed a linear relationship between the cardiologist’s dose and the total dose of the patient.
Keywords: occupational exposure, Radiation Exposure, Coronary Angiography, Interventional Radiology Monte Carlo -
Pages 314-320IntroductionThe study aimed to assess the effectiveness of the dosimetric parameters of organs-at-risks (OARs) and target coverage in optimized plans compared to non-optimised plans normalized at point A.Material and MethodsThis retrospective study examined 21 patients with cervical cancer in stages II and III, who had undergone a high dose rate (HDR) ICBT following external beam radiotherapy(EBRT).In this study, two treatment plans were created for each case using computed tomography (CT) images. Normalization at point A was performed in the non-optimised plans, and 90% of the high-risk clinical target volume (HR-CTV) was to receive the prescribed dose in the optimised plans. Dose-volume histograms (DVH) were used to compare D5cc, D2cc, D1cc, and D0.1cc (minimum doses received by the most irradiated volumes of5cc, 2cc, 1cc and 0.1cc, respectively) for OARs as well as the D90%, D50%, D98%, D100%, and D95% coverage of HR-CTV between the non-optimised and optimised plans. Statistical analysis was performed using Wilcoxon signed rank test.ResultsThe HR-CTV coverage improved in 80% of the patients. In the optimised plans, the rectum and bladder doses decreased by 8.75% and 9.85%, as compared to the non-optimised plans normalized at point A, respectively. In the sigmoid and bowel cases, there were dose drops by 8.95% and 9.75%, in the optimised plans, respectively.ConclusionTarget coverage and OAR sparing were more satisfactory in the optimised plans than the non-optimised plans normalized at point A.Keywords: Brachytherapy, High risk CTV, carcinoma cervix, Intermediate Risk CTV, ICRU Report 89
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Pages 321-330IntroductionThe present study focused on the dosimetric evaluation of Edge and Novalis Tx (NTx) linear accelerator (LA)-based radiosurgery system by using RapidArc (RA) and dynamic conformal arc (DCA) planning techniques.Material and MethodsForty patients with brain lesions of variable sizes (1.1-15.98 cc) were planned for Edge and NTx system by using the RA and DCA planning techniques on eclipse treatment planning system, version 13.6 (Varian Medical Systems, Palo Alto, CA, USA). All the plans were evaluated on the basis of paddick conformity index (PCI), homogeneity index (HI), and gradient index (GI). The maximum doses to organs at risk (OAR), V12Gy, V10Gy, and V5Gy for healthy brain tissue were also evaluated for all the plans. The treatment delivery efficiency for both systems was also evaluated.ResultsThe mean PCI and GI for both RA and DCA plans were found to be better in Edge as compared to NTx system (PCI Edge, RA=0.77±0.1, PCI NTx, RA=0.66±0.11, PCI Edge, DCA= 0.69±0.12, PCI NTx,DCA= 0.67±0.12). Significant differences in HI, doses to OAR, and V12Gy, V10Gy, and V5Gy brain volume were observed for both systems with p-value less than 0.05. Reduced treatment time was observed in Edge LA as compared to NTx LA.ConclusionEdge LA produced clinically better target volume conformity, rapid dose fall-off, and reduced reduction in normal brain volume irradiation and treatment time compared to NTx. Thus, in the set of patient plans evaluated, it was noted that Edge stereotactic suite is more efficacious and diametrically suitable for intracranial radiosurgery.Keywords: dynamic conformal arc, Linac, Stereotactic radiosurgery, Treatment Planning
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Pages 331-338IntroductionTomotherapy beam delivery is in the helical form. Therefore, the dose distribution will be more complex while target is moving. In this study, we sought to evaluate the dosimetric impact due to longitudinal motion in the phantom of a tomotherapy machine.Material and MethodsCheese and Delta4 phantom+ were placed on a respiratory motion platform. They moved in longitudinal directions at the amplitudes of 2, 4, 6, 8, and 10 mm. The period of that movement was 4 and 6 s with the field widths of 25 and 50 mm, respectively. The C-shaped complex target was modified according to the American Association of Physicists in Medicine (AAPM) Task Group (TG) 119. The planning verifications were evaluated through point dose, gamma index value, and dose-volume histogram (DVH).ResultsDiscrepancy of the dose measurements ranged from -1.254 to -14.421%. The range of gamma index value was 61.2 ±1.23% to 100±0.00. The DVH evaluation showed that the homogeneity index (HI) and the minimum dose to receive by 95% (D95%) of the target structure were 0.247 to 0.389 and -0.061 to -0.271 Gy, respectively. The maximum dose (DMax) of the organ at risk (OAR) structure was 0.082 to 0.327 Gy.ConclusionThe motion could induce dose discrepancies in tomotherapy dose distribution. The selection of the jaw field width in tomotherapy is crucial for intensity-modulated radiotherapy (IMRT) techniques with moving targets. For larger field widths, the dose discrepancy between the planned and measured doses exhibited an excellent result for gamma index and dose coverage.Keywords: Tomotherapy, Intensity Modulated Radiotherapy, Dosimetric Impact
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Pages 339-345IntroductionDiffusion tensor imaging (DTI) is typically obtained by echo-planar imaging (EPI) to map the human brain. However, EPI is sensitive to susceptibility effects, requiring elaborate image post-processing. Besides, DTI alone is limited in assessing gray and white matter boundaries of the brain, which has important implications for obtaining accurate images from brain atrophy. This study aimed to design and evaluate simultaneous diffusion and T1 weighting high-resolution imaging for human brain mapping.Material and MethodsThe method of T1 weighted three-dimensional Magnetization-prepared rapid gradient-echo (T1w 3D MPRAGE), which is conventionally used for structural brain mapping of gray and white matter, was extended to incorporate diffusion encoding using simulation and experiment to develop high-resolution DTI and T1-weighted human brain data.ResultsTheoretical simulations, as well as experimental results from in-vivo human brain studies at 4 Tesla magnetic field strength, showed that the DTI contrast, including fractional anisotropy (FA) and mean diffusivity (MD), incorporated into T1w 3D MPRAGE improves the contrast between gray and white matter sub-structural boundaries. Moreover, diffusion encoding into 3D MPRAGE avoids the inherent image distortions typically seen in EPI-based DTI.ConclusionThis study suggests the capability and effectiveness of the combined DTI weighted 3D MPRAGE and T1 weighted for improving the detection of gray/white matter boundaries in human brain imaging.Keywords: T1, 3D MPRAGE, diffusion MRI, Contrast, DTI, human brain
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Pages 346-351Introduction
The long-half-life Cobalt-60 source with high dose rate (HDR) brachytherapy is an appropriate alternative to Iridium-192 (HDR) source in the treatment of GYN patients in developing countries. This study aimed to compare HDR cervical cancer treatment duration using Cobalt-60 and Iridium-192 sources for the Tandem-ovoid applicators.
Material and MethodsIn the present study, BEBIG Cobalt-60 source model Co0.A86 and Iridium-192 source model mHDR-v2r were utilized. The treatment time required for both radionuclides was calculated using the TG-43 formalism. To calculate the treatment time for the Iridium source, the absorbed dose was used in the TG-43 formalism and treatment data. Then the dwell times were determined after repeating the calculations with Cobalt-60. Finally, the comparison was made for the treatment duration for the two sources.
ResultsAccording to our findings, the treatment time for the cobalt source with the activity of 2.131 Ci is somehow the same as that of the iridium source with the activity of 5.690 Ci. If the maximum treatment duration is supposed to be 16 minutes in a treatment session, the effective time window for Iridium-192 is about 160 days. This is, however, the effective time window is 2000 days for Cobalt-60.
ConclusionAccording to the findings, the use of Cobalt-60 instead of Iridium-192 is economically beneficial for equipment selection in newly constructed departments. Changes in the activities of Cobalt-60 in comparison with Iridium-192 requires editing the total treatment time of the treatment planning system for patients. Such editing may raise errors and reduce accuracy.
Keywords: Treatment Time, Absorbed Dose Brachytherapy -
Pages 352-360IntroductionIn this study, we aimed to evaluate internal (lung, heart and diaphragm) and external (nine glass marbles) marker motion in correlation with lung tumor motion and determine potential surrogate for respiratory gating radiation therapy (RGRT) depending on tumor localization, upper lobe (UL) versus lower lobe (LL).Material and MethodsWe included 58 patients (34 male and 24 female) with small lung cancer (≤ 5cm), who underwent stereotactic body radiation therapy (SBRT). All patients were scanned and contoured in all ten phases (Varian Eclipse 13.7) after four-dimensional computed tomography simulation (4D-CT). The motions of internal and external markers were analyzed and correlated with tumor motion. Pearson correlation coefficient (PCC) was used to evaluate the correlation between internal and external marker motion and tumor motion.ResultsThe median (range) values of tumor motion were 3.2 (0.6-11.0) and 8.6 (4.0-24.0) mm in the UL and LL, respectively. The median (range) values of organs motion and PCC comparing UL vs. LL were 2.0 (0.3-9.1) vs. 6.0 (2.8-13.9) mm and 0.46 (0.30-0.95) vs. 0.79 (0.50-0.94) for the lung, respectively, 11.9 (2.5-16.3) vs. 12.5 (5.0-22.5) mm and 0.68 (0.11-0.93) vs. 0.89 (0.30-0.99) for the diaphragm, respectively, and 3.9 (2.5-6.3) vs. 7.6 (4.5-8.6) mm and 0.49 (0.20-0.70) vs. 0.59 (0.36-0.83) for the heart, respectively. The external marker motion and correlation coefficient for UL and LL were 2.5 (0.9-7.4) vs. 2.3 (1.0-5.9) mm and 0.54 (0.09-0.96) vs. 0.73 (0.27-0.94), respectively.ConclusionLung and diaphragm motion correlate better with tumor motion than the external marker. Diaphragm motion can be an excellent indicator for treatment based on RGRT.Keywords: Lung Cancer Motion Surrogate Marker Four, Dimensional Computed Tomography Stereotactic Body Radiotherapy
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Pages 361-368IntroductionPhotochemical internalization is a novel PDT-based technology for the intracellular delivery of hydrophilic macromolecular therapeutic agents and other drugs limited in penetration into cellular membranes with intracellular targets. In this regard, one of the approaches is to use nanoparticles along with photosensitizing agents. In this study, the presence of thioglucose-coated gold nanoparticles in the efficiency of the photodynamic effect of methylene blue (MB) caused by the photochemical internalization phenomenon was investigated.Material and MethodsFirst, Glu-GNPs was synthesized, and then the toxicity of Glu-GNPs and MB were determined to achieve their optimal concentrations. Afterward, the photodynamic effects of Glu-GNPs combined with MB by Luma-Care source light were evaluated at different doses using MTT assay and colony assay (12 days after treatment).ResultsAccording to the MTT assay, the photodynamic effect in the Glu-GNPs group revealed no significant efficacy, whereas the colony-formation capability in all groups with an optical dose of 15.6 J / cm2 decreased, compared to the similar group without light exposure (P < 0.05).ConclusionThe photodynamic efficiency of MB with the Glu-GNPs group was reduced at 15.6 J/cm2, compared to the free MB group. The decreased efficiency can have various reasons such as the photochemical bleaching of the free MB because of ROS and 1O2 produced by the plasmonic photodynamic phenomenon of Glu-GNPs or changing the optophysical properties of surface plasmon resonance of final product (MB+ Glu-GNPs) due to the possible electrostatic bonding of the drug with the nanoparticles.Keywords: Breast Cancer, Photodynamic Therapy (PDT), Gold Nanoparticles (GNPs) Methylene Blue (MB)
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Pages 369-375IntroductionOne of the most important components in radiotherapy with external surrogates is utilizing consistent correlation model to estimate tumor location as model output on the basis of external markers motion dataset. In this study, imperialist competitive algorithm (ICA) was proposed to process and optimize motion dataset for correlation model. The simplicity of correlation model based on this algorithm may result in less targeting error with the least computational time.Material and MethodsA correlation model based on adaptive neuro-fuzzy inference system (ANFIS) was utilized with database of 20 patients treated with CyberKnife Synchrony system. In order to assess the effect of proposed data optimization algorithm, two strategies were considered. The correlation model was used with and without implementing ICA. Then, targeting error of ANFIS model was compared at two strategies using statistical analysis.ResultsThe results showed that implementing the proposed algorithm on ANFIS model could remarkably improve the performance accuracy of ANFIS correlation model by eliminating unnecessary and noisy inputs and making the model simpler. Moreover, model simplicity factor could highly reduce model computational time, which is attractive for clinical practice.ConclusionICA was proposed as data optimization algorithm on motion dataset of patients treated with external surrogates’ radiotherapy. Our proposed algorithm could highly optimize the input motion dataset of correlation model for estimating tumor position by selecting enough data points with high degree of importance. The final results showed an improvement of targeting accuracy of correlation model, as well as a significant reduction at model computational time.Keywords: Targeted radiotherapy, Surrogates, Correlation of Data, optimization
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Pages 376-383IntroductionA simple noise reduction algorithm, i.e. a selective mean filter (SMF), had been previously introduced. The aim of this study is to investigate the image qualities filtered by a SMF and its comparison to an adaptive statistical iterative reconstruction (ASIR).Material and MethodsTo assess the basic image quality, an American Association of Physicists in Medicine Computed Tomography (AAPM CT) performance phantom was used. The phantom was scanned by 128 Multiple Slices Computed Tomography. The tube current varied from 50 mA to 100, 150, and 200 mA. The images of a phantom were reconstructed by filtered back projection (FBP) followed by SMF and ASIR (20, 40, 60, 80, and 100%). The image quality assessment was in terms of noise level, noise power spectrum (NPS), and modulation transfer function (MTF).ResultsThe noise level and NPS of SMF was similar with ASIR 100%. The values of the MTF10 of the ASIR filter at any level and SMF were comparable. The MTF10 values of ASIR 60%, and SMF with 50 mA (low) were 0.76 ± 0.02 and 0.75 ± 0.02 cycle/mm, respectively. Meanwhile, the MTF10 of ASIR 60% and SMF with 200 mA (high) were 0.74 ± 0.00 and 0.73 ± 0.00 cycles/mm, respectively.ConclusionOur results indicated that the performance of the SMF in reducing noise is equivalent to the maximum level of ASIR strength, i.e., ASIR 100%.Keywords: Computed Tomography, Image Quality, Algorithms, Image Processing, selective mean filter, adaptive statistical iterative reconstruction