The influence of patient positioning and immobilization equipment on MR image quality and image registration in radiation therapy.

INTRODUCTION: MRI is preferred for brain tumor assessment, while CT is used for radiotherapy simulation. This study evaluated immobilization equipment's impact on CT-MRI registration accuracy and MR image quality in RT setup. METHODS: We included CT and MR images from 11 patients with high-grade glioma, all of whom were immobilized with a thermoplastic mask and headrest. T1- and T2-weighted MR images were acquired using an MR head coil in a diagnostic setup (DS) and a body matrix coil in RT setup. To assess MR image quality, signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were considered in some dedicated regions of interest. We also evaluated the impact of immobilization equipment on CT-MRI rigid registration using line profile and external contour methods. RESULTS: The CNR and SNR reduction was in the RT setup of imaging. This was more evident in T1-weighted images than in T2-weighted ones. The SNR decreased by 14.91% and 12.09%, while CNR decreased by 25.12% and 20.15% in T1- and T2-weighted images, respectively. The immobilization equipment in the RT setup decreased the mean error in rigid registration by 1.02 mm. The external contour method yielded Dice similarity coefficients (DSC) of 0.84 and 0.92 for CT-DS MRI and CT-RT MRI registration, respectively. CONCLUSION: The image quality reduction in the RT setup was due to the imaged region's anatomy and its position relative to the applied coil. Furthermore, optimizing the pulse sequence is crucial for MR imaging in RT applications. Although the use of immobilization equipment may decrease the image quality in the RT setup, it does not affect organ delineation, and the image quality is still satisfactory for this purpose. Also, the use of immobilization equipment in the RT setup has increased registration accuracy.

Monte Carlo-based calculation of nano-scale dose enhancement factor and relative biological effectiveness in using different nanoparticles as a radiosensitizer.

INTRODUCTION: Nowadays, some nanoparticles (NPs) are known and used as radiosensitizers in radiotherapy and radiobiology, due to their desired biological, physical, and chemical effects on cells. This study aimed to evaluate and compare the dose enhancement factor (DEF) and the biological effectiveness of some common NPs through EGSnrc and MCDS Monte Carlo (MC) simulation codes. MATERIALS AND METHODS: To evaluate considered NPs' DEF, a single NP with 50 nm diameter was simulated at the center of concentric spheres. NP irradiations were done with 30, 60, and 100 keV photon energies. The secondary electron spectra were scored at the surface of considered NPs, and the dose values were scored at surrounding water-filled spherical shells which were distributed up to 4000 nm from the NP surface. The electron spectra were used in the MCDS code to obtain different initial DNA damages for the calculation of enhanced relative biological effectiveness (eRBE). RESULTS: By decreasing the photon energy, an increment of DEF was seen for all studied NPs. The maximum DEF at 30, 60, and 100 keV photon energies were respectively related to silver (Ag), gadolinium (Gd), and bismuth (Bi) NPs. The maximum double-strand break (DSB) related (eRBEDSB) values for the 30 keV photon belonged to Ag, while BiNPs showed the maximum values at other photon energies. The minimum eRBEDSB values were also related to iron (Fe) NPs at the entire range of studied photon energies. CONCLUSIONS: The compared nanoscale physical and biological results of our study can be helpful in the selection of optimum NP as a radiosensitizer in future radiobiological studies. Bi, gold (Au), Ag, and platinum (Pt) NPs had great potential, respectively, as radiosensitizers relative to the other studied NPs.

Evaluation of the heart and lung dosimetric parameters in deep inspiration breath hold using 3D Slicer.

PURPOSE: The present study was conducted to compare dosimetric parameters for the heart and left lung between free breathing (FB) and deep inspiration breath hold (DIBH) and determine the most important potential factors associated with increasing the lung dose for left-sided breast radiotherapy using image analysis with 3D Slicer software. MATERIALS AND METHODS: Computed tomography-simulation scans in FB and DIBH were obtained from 17 patients with left-sided breast cancer. After contouring, three-dimensional conformal plans were generated for them. The prescribed dose was 50 Gy to the clinical target volume. In addition to the dosimetric parameters, the irradiated volumes and both displacement magnitudes and vectors for the heart and left lung were assessed using 3D Slicer software. RESULTS: The average of the heart mean dose (Dmean) decreased from 5.97 to 3.83 Gy and V25 from 7.60% to 3.29% using DIBH (p < 0.001). Furthermore, the average of Dmean for the left lung was changed from 8.67 to 8.95 Gy (p = 0.389) and V20 from 14.84% to 15.44% (p = 0.387). Both of the absolute and relative irradiated heart volumes decreased from 42.12 to 15.82 mL and 8.16% to 3.17%, respectively (p < 0.001); however, these parameters for the left lung increased from 124.32 to 223.27 mL (p < 0.001) and 13.33% to 13.99% (p = 0.350). In addition, the average of heart and left lung displacement magnitudes were calculated at 7.32 and 20.91 mm, respectively. CONCLUSION: The DIBH is an effective technique in the reduction of the heart dose for tangentially treated left sided-breast cancer patients, without a detrimental effect on the left lung.

Dosimetric investigation of a new high dose rate 192Ir brachytherapy source, IRAsource, by Monte Carlo method.

PURPOSE: The purpose of the present study was to perform an independent calculation of dosimetric parameters associated with a new 192Ir brachytherapy source model, IRAsource. MATERIALS AND METHODS: The parameters of air kerma strength (AKS), dose rate constant (DRC), geometry function (GF), radial dose function (RDF), as well as two-dimensional (2D) anisotropy function (AF) of IRAsource 192Ir source model were calculated in this study. The MC n-particle extended (MCNPX) code was also employed for simulating high dose rate (HDR), IRAsource and 192Ir source; and formalism was used for calculating dosimetry parameters based on task group number 43 updated report (TG-43 U1). RESULTS: The results of this study were consistent with the ones reported about the IRAsource source by Sarabiasl et al. The AKS per 1 mCi activity and the DRC values were also equal to 3.65 cGycm2 h-1 mCi-1 and 1.094 cGyh-1U-1; respectively. The comparison of the results of the DRC and the RDF reported by Sarabiasl et al. also validated the 192Ir IRAsource simulation in this study. Moreover, the AFs of IRAsource source model were in a good agreement with those of Sarabiasl et al. at different distances, which could be attributed to identical geometries. CONCLUSION: In line with those reported by Sarabiasl et al., the results of this study confirmed the IRAsource 192Ir source for clinical uses. The calculated dosimetric parameters of the IRAsource source could be utilized in clinical practices as input data sets or for validation of treatment planning system calculations.

Increased radiotoxicity in two cancerous cell lines irradiated by low and high energy photons in the presence of thio-glucose bound gold nanoparticles.

PURPOSE: Gold nanoparticles modified by thio-glucose are believed to increase the toxicity of radiotherapy in human malignant cells. We report the effect of thio-glucose bound gold nanoparticles (Glu-G nanoparticles), 16 nm in size, on two human lung (QU-DB) and breast (MCF7) cancer cell lines combined with kilo and megavoltage X-rays. MATERIALS AND METHODS: The shape and surface characteristics, the size distribution and light absorption spectrum of the prepared nanoparticles were measured by transmission electron microscopy, dynamic light scattering, and ultraviolet-visible spectrophotometry, respectively. The cell uptake was assayed using the atomic absorption spectrometry. Mitochondrial activity, colony formation, and comet assays were applied to assess and compare the enhanced radiotoxicity of 100 KV and 6 MV X-rays, when combined with Glu-G nanoparticles. RESULTS: Glu-G nanoparticles had no significant toxicity for MCF7 and QU-DB cells up to 100 micromolar concentration. Compared to radiation alone, the intracellular uptake of Glu-G nanoparticles resulted in increased inhibition of cell proliferation by 64.1% and 38.7% for MCF7 cells, and 64.4% and 32.4% for QU-DB cells by 100 kVp and 6 MV X-rays, respectively. Comet assay confirmed an increase of DNA damage as a result of combination of 6 MV photons with Glu-G nanoparticles. CONCLUSION: Glu-G nanoparticles have remarkable potential for enhancing radiotoxicity of both low and high energy photons in MCF7 and QU-DB cells.

Comparison of the hypothetical (57)Co brachytherapy source with the (192)Ir source.

AIM OF THE STUDY: The (57)Co radioisotope has recently been proposed as a hypothetical brachytherapy source due to its high specific activity, appropriate half-life (272 days) and medium energy photons (114.17 keV on average). In this study, Task Group No. 43 dosimetric parameters were calculated and reported for a hypothetical (57)Co source. MATERIAL AND METHODS: A hypothetical (57)Co source was simulated in MCNPX, consisting of an active cylinder with 3.5 mm length and 0.6 mm radius encapsulated in a stainless steel capsule. Three photon energies were utilized (136 keV [10.68%], 122 keV [85.60%], 14 keV [9.16%]) for the (57)Co source. Air kerma strength, dose rate constant, radial dose function, anisotropy function, and isodose curves for the source were calculated and compared to the corresponding data for a (192)Ir source. RESULTS: The results are presented as tables and figures. Air kerma strength per 1 mCi activity for the (57)Co source was 0.46 cGyh(-1) cm 2 mCi(-1). The dose rate constant for the (57)Co source was determined to be 1.215 cGyh(-1)U(-1). The radial dose function for the (57)Co source has an increasing trend due to multiple scattering of low energy photons. The anisotropy function for the (57)Co source at various distances from the source is more isotropic than the (192)Ir source. CONCLUSIONS: The (57)Co source has advantages over (192)Ir due to its lower energy photons, longer half-life, higher dose rate constant and more isotropic anisotropic function. However, the (192)Ir source has a higher initial air kerma strength and more uniform radial dose function. These properties make (57)Co a suitable source for use in brachytherapy applications.

The effect of glucose-coated gold nanoparticles on radiation bystander effect induced in MCF-7 and QUDB cell lines.

Due to biocompatibility and relative non-toxic nature, gold nanoparticles (GNPs) have been studied widely to be employed in radiotherapy as radio-sensitizer. On the other hand, they may enhance radiation-induced bystander effect (RIBE), which causes radiation adverse effects in non-irradiated normal cells. The present study was planned to investigate the possibility of augmenting the RIBE consequence of applying glucose-coated gold nanoparticles (Glu-GNPs) to target cells. Glu-GNPs were synthesized and utilized to treat MCF7 and QUDB cells. The treated cells were irradiated with 100 kVp X-rays, and their culture media were transferred to non-irradiated bystander cells. Performing MTT cellular proliferation test and colony formation assay, percentage cell viability and survival fraction of bystander cells were determined, respectively, and were compared to control bystander cells which received culture medium from irradiated cells without Glu-GNPs. Glu-GNPs decreased the cell viability and survival fraction of QUDB bystander cells by as much as 13.2 and 11.5 %, respectively (P < 0.02). However, the same end points were not changed by Glu-GNPs in MCF-7 bystander cells. Different RIBE responses were observed in QUDB and MCF7 loaded with Glu-GNPs. Glu-GNPs increased the RIBE in QUDB cells, while they had no effects on RIBE in MCF7 cells. As opposed to QUDB cells, the RIBE in MCF7 cells did not change in the dose range of 0.5-10 Gy. Therefore, it might be a constant effect and the reason of not being increased by Glu-GNPs.