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Introduction: For decades, hyperthermia had been widely used for tumor ablation by increasing the temperature of cancerous tissues. For clinical treatment, a capacitance system was developed around the world. In this study, a capacitance system of radiofrequency (RF) hyperthermia was simulated to achieve the temperature distribution map of the entire breast equivalent phantom. Therefore, the efficiency of this method in the treatment of breast cancer was investigated in the current study. Material and Methods: In this study, an RF system with a frequency of 13.56 MHz was simulated by Comsol Multiphysics software (Version 5.3). The geometry of the breast cancerous tissue was modeled by the consideration of three different tissues, including the fat, gland, and tumor tissues. The two electrodes of the system were modeled as two disks with a radius of 15 cm. The calculations of the RF wave and bioheat equation were accomplished by numerical simulation and finite element method. Results: The temperature plots were obtained in 5 min. The temperature distribution map was entirely achieved and the results were compared with experimental findings to check the accuracy of the RF device and precision of the thermometer. Conclusion: The obtained results showed that the temperature of the whole tumor region increased uniformly (3-4°C). Moreover, the temperature of the whole healthy tissues (i.e., the gland and fat tissues) did not increase (1.9-2.1°C). Consequently, in the capacitive hyperthermia system, the tumor reached extreme heat; however, the healthy tissues were completely protected from damages. [ABSTRACT FROM AUTHOR]

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 volume histograms (DVHs) for single-shot irradiations of the Gamma Knife (GK) unit were used to investigate the effects of the presence of inhomogeneities on 3D dose distribution. The head phantom was a custom-built 16 cm diameter Plexiglas sphere. Inside the phantom, there is a cubic cutout for inserting the gel vials and another cutout for inserting the inhomogeneities. Following irradiation with the GK unit, the polymer gel phantoms were scanned with a 1.5 T MRI scanner. Comparing the results of measurement in homogeneous and heterogeneous phantoms revealed that inserting inhomogeneities inside the homogeneous phantom did not cause considerable disturbances on dose distribution in irradiation with 8 mm collimator within low isodose levels (<50%), which is essential for the dose sparing of sensitive structures. The results of simulation for homogeneous and inhomogeneous phantoms in irradiation with 18 mm collimator of the GK unit showed 23.24% difference in DVH within 90%–100% relative isodose level and also revealed that a significant part of the target (28.56%) received relative doses higher than the maximum dose, which exceeds the acceptance criterion (5%). Based on these results it is concluded that the presence of inhomogeneities inside the phantom can cause considerable errors in dose calculation within high isodose levels with respect to LGP prediction which assumes that the target is a homogeneous material. Moreover, it is demonstrated that the applied MC code is an accurate and stand-alone tool for 3D evaluation of dose distribution in irradiation with the GK unit, which can provide important, 3D plan evaluation criteria used in clinical practice. [ABSTRACT FROM AUTHOR]

Metal-organic frameworks (MOFs) have shown a great potential as a novel contrast agent in magnetic resonance imaging (MRI) due to their unique properties including versatile structures, composition, and surface chemistry. Fe-MIL-88B-NH2 (MILs) was synthesized using Fe+3 ions and 2-aminoterephthalic acids (NH2-BDC) in the presence of acetic acid and Pluronic F127 under a hydrothermal process. Three MILs in different sizes were synthesized by using variant CH3COOH/Fe+3 molar ratios and denoted as MIL-S, MIL-M, and MIL-L having average sizes of 60, 350, and 730 nm, respectively. The effect of aspect ratio and particle size of MILs was investigated on proton relaxivity and contrast enhancement in aqueous, in vitro, and in vivo MR images. MRI study indicated that by increasing the MILs size, the incremental transverse relaxivity was achieved from 13.53 to 50.80 for r2 and from 38.75 to 60.25 for r2*, while the difference between r2 and r2* was decreased obviously. The r2/r1 ratios were found to be 5.80, 42.27, and 127.00 for MIL-S, MIL-M, and MIL-L, respectively. All MILs demonstrated T2-weighted MR imaging performance. Furthermore, no susceptibility artifacts were observed on T2-weighted images of MILs. By decreasing the size of MILs, r2/r1 ratio was reduced sharply and T1 contrast was also observed for MIL-S. MIL-S was used for in vitro and in vivo study due to its capability in simultaneous T1 and T2 contrast enhancements. MTT and hemolysis assays showed no significant cytotoxicity and hemolysis for MIL-S against normal human breast cell line (MCF-10A) and red blood cells, respectively, at concentrations of Fe+3 up to 300 μg/mL (p < 0.05). T1-weighted images acquired from in vitro study interestingly showed that the signal intensity of MIL-S is more than Dotarem. The in vivo experiment revealed that the signal intensity of mice liver decreased sharply after injection resulting in increase of negative contrast enhancement. The negative contrast enhancement decreased gradually by the time under T2-weighted imaging mode confirming application of MIL-S as a T2 contrast agent in biomedical applications (up to 12 h post-injection). Although a decrease of the size resulted in bright contrast in aqueous solution for MIL-S, it did not show proper efficiency for in vivo positive contrast enhancement. The advantages, including simple preparation and accessibility, acceptable potency and selectivity, blood compatibility, and suitable cytocompatibility as well as enough circulation time, make MIL-S as a dual MRI contrast agent to differentiate between low-contrast tissues for in vivo experiments. [ABSTRACT FROM AUTHOR]