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Introduction: Patient repositioning in treatment radiotherapy is one of the main factors that increase error of target irradiation. However additional margin is necessary to consider the uncertainties created along and around X, Y and Z-axis.Material and Methods: Set-up and random errors were calculated in translational and rotational axis for a sample of 20 prostatic patients; using daily IGRT-CBCT method. The aim of this study was to determine the additional margin that should be added from clinical target volume (CTV) to prevent toxicity and increase the irradiation precision in radiotherapy. The van Hark formula (PTV margin =2.5Σ +0.7σ) was used for all patients to perform PTV margin for prostatic localization.Results: The research performed for a sample of 20 consecutive patients. With respect to systematic error along the lateral axis, longitudinal and anterior-posterior was 2.32, 2.42 and 3.54 respectively. The Random error was 1.82, 2.19 and 1.76° along lateral axis, longitudinal and anterior-posterior respectively. The rotational systematic error was 1.49, 2.04 and 2.14° around lateral, longitudinal and anterior-posterior axis respectively. The Random error was 1.78, 1.75 and 1.63° around lateral, longitudinal and anterior-posterior axis respectively. The calculated safety margin to cover clinical target volume (CTV) taking the prostate variability into account measured 7.55, 8.08 and 10.79 mm for lateral, longitudinal and anterior posterior respectively and 7mm would be enough in the posterior side. Rotational set-up errors for almost 95% of patients were between -2° and 2°.Conclusion: The calculated safety margin in all direction was smaller than 1 cm except in anterior side that was 1 cm or more.

Introduction: In Yttrium-90 SPECT imaging, the energy window and collimator used during projection acquisition can significantly affect image quality. In this work, we used a new and independent method to verify previous results, which suggest suitable energy around 130 keV. Material and Methods: We used Siemens Symbia SPECT-CT system fitted with High Energy General Purpose (HEGP), Medium Energy General Purpose (MEGP), and Low Energy High Resolution (LEHR) to acquire data from NEMA IEC PET Body Phantom filled with 90Y chloride. ISO-counting curve is a new method analysed in this study to evaluate the adequate parameters for 90Y SPECT imaging. Results: HEGP collimator was the most suitable for acquisitions of 90Y bremsstrahlung radiation from the point of view of the correct volume reproduction. ISO-counting analyses have shown that for the bigger phantom spheres, the optimum acquisition energy is centered on 130 keV. Conclusion: The ISO-counting curve method is consistent to previous studies’ results and can help to improve image quality.

Introduction: In yttrium-90 imaging, image quality is highly dependent on the selection of energy window and collimator design becausetheY-90 bremsstrahlung photons have a continuous and broad energy distribution. The current study aimed to optimize the bremsstrahlung energy window setting and collimator for the improvement of both resolution and sensitivity. Material and Methods: In the present study, simulation of medical imaging nuclear detectors (SIMIND) Monte Carlo program was used to simulate Siemens Medical System Symbia. The SIMIND was utilized to generate the Y-90 bremsstrahlung single-photon emission computed tomography (SPECT) projection of the point source. Six energy windows settings and two collimators denoting medium energy and high energy were used in order to assess the effect of the energy window on the resolution. Results: The experimental measurements and simulation results showed a similar pattern in the point spread functions with the energy window. The simulation data indicated that the geometric component reached 73%for the energy window within the range of51-120keVusingthe high-energy (HE) collimator. In addition, the obtained results showed that the full width at half maximum (FWHM) and full width at tenth maximum (FWTM)(FWHM=7mm and FWTM=35mm)were higher in this window in comparison to those reported for other windows. Conclusion: According to the obtained results of the present study, the optimal energy window for Y-90 bremsstrahlung SPECT imaging was within the range of 51-120 keV. The obtained optimal energy window and optimal HE collimator had the potential to improve the image resolution and sensitivity of Y-90 SPECT images

Introduction: In radionuclide imaging, object scatter is one of the major factors leading to image quality degradation. Therefore, the correction of scattered photons might have a great impact on improving the image quality. Regarding this, the present study aimed to determine the main and sub-energy windows for triple energy window (TEW) scatter correction method using the SIMIND Monte Carlo simulation code in Gadolinium-159 (Gd-159) imaging. Material and Methods: The energy window was set for various main energy window widths (i.e., 10%, 15%, and 20%) and sub-energy window widths (i.e., 3 and 6 keV).Siemens Medical System Symbia fitted with a high-energy collimator was used with Gd-159 point source positioned at seven locations inside the cylindrical water phantom. A comparison was made between the true primary to total ratio (calculated by SIMIND) and the primary to total ratio estimated using TEW method. Results: The findings of this study showed that 20% of the main energy windows with 3 and 6 keV sub-energy windows were optimal for the implementation of the TEW method in Gd-159. Conclusion: According to the results, the optimal energy windows for Gd-159 scintigraphy were the sub-energy windows of 3 and 6 keV. These findings could be helpful in the quantification of Gd-159 imaging.Purpose : In radio-nuclides imaging, object scatter is one of major factors which leads to degradation of image quality. Therefore, the correction of scattered photons has a great impact to improve the image quality. The aim of this work was to determine the main and sub-energy windows for the triple energy window (TEW) scatter correction method using Monte Carlo simulation SIMIND code for Gadolinium-159 (Gd-159) imaging. Methods : Energy window was set for various main energy window width (10,15 and 20%) and sub energy window width (3 and 6 keV). Siemens Medical System Symbia fitted with High Energy collimator (HE) was imaged with Gd-159 point source positioned at seven locations inside cylindrical water phantom. The true primary to total ratio (calculated by SIMIND) and the primary to total ratio estimated using TEW method were compared.Results : A 20% of main energy window with 3 and 6 keV sub-energy windows were found to be optimal for implementation of the TEW method in Gd-159. Conclusion: The obtained results provide the optimal energy window for Gd-159 scintigraphy data and will aid the quantification of Gd-159 imaging.