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Liposomes
Published in Sourav Bhattacharjee, Principles of Nanomedicine, 2019
ThermoDox®: It is a thermosensitive PEGylated stealth liposomal preparation of doxorubicin for intravenous administration in hepatocellular carcinoma and recurring breast cancer while developed by Celsion Corporation, New Jersey, USA [183–185]. The lipid constituents are DPPC, myristoylstearoyl phosphatidylcholine (MSPC), and DSPEPEG2000 [186, 187]. The Tc of DPPC is ~42°C, although it is lowered slightly in the presence of MSPC. The stealth properties are provided by DSPE-PEG2000. Such lipid composition makes these liposomes unstable, with increased permeability at local hyperthermia (39.5°C–42°C) achieved by radiofrequency ablation, microwave-assisted techniques, or high-intensity ultrasound [188]. After intravenous administration, ThermoDox® showed a 5-fold to 25-fold higher drug concentration in a hepatic tumor compared to intravenously administered doxorubicin or its liposomal formulations. It is currently designated as an orphan drug by the FDA and EMA while multiple phase III trials are on.
Imaging in oncology
Published in David A Lisle, Imaging for Students, 2012
Percutaneous tumour ablation may be used to treat tumours of the liver, kidney, breast, bone or lung. US, CT or MRI may be used for procedure guidance. A variety of ablation techniques is available under three broad categories:Injection of substances that cause cell death, such as ethanol or heated salineHeatingRadiofrequency ablationInterstitial laser therapyMicrowave coagulationHigh intensity focused ultrasound (HIFU)Freezing: cryotherapy.
Thermal Therapy Applications of Electromagnetic Energy
Published in Ben Greenebaum, Frank Barnes, Biological and Medical Aspects of Electromagnetic Fields, 2018
P.R. Stauffer, D.B. Rodrigues, D. Haemmerich, C.-K. Chou
In contrast to hyperthermia, which elevates tumor temperature to less than 45°C, radiofrequency ablation applies RF electric fields (450–500 kHz) to produce ionic currents in tissue and cause resistive heating to at least 50°C. Direct heating is limited to tissue in close proximity to the RF electrode, while more distant tissue is indirectly heated through thermal conduction (Figure 9.6). Temperatures greater than 100°C are generally avoided to prevent tissue boiling, vaporization, and carbonization. These phenomena cause a large increase in tissue impedance around the electrode that restricts RF current and limits further extent of heating. Therefore, the goal of RFA is to achieve and maintain a temperature in the range of 50–100°C throughout the target volume. This therapeutic window is much larger than the 40–45°C window for hyperthermia, thus requiring less uniform distribution of power deposition than for hyperthermia applications. Still, the power applied to the RF electrode must be controlled to maintain tissue temperatures in this desired range. Often, a temperature sensor (thermistor or thermocouple) is integrated into the electrode to allow monitoring of electrode temperature, and applied power is adjusted based on surface temperature of the electrode. Other approaches include application of a prescribed constant power level for a given time period, or the use of tissue impedance as measured between the RF electrode and the dispersive electrode (ground pad) for feedback control signal. Typical power levels for RFA devices are in the range of 100–250 W. Figure 9.6 depicts the electric field strength and corresponding temperature distribution surrounding an internally-cooled RF electrode inserted in soft tissue like muscle or tumor.
Study of heat sink effect of blood in a bifurcated vessel
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2023
Sidharth Sankar Das, Swarup Kumar Mahapatra
Thermal analysis of biological tissues and blood flow through and adjacent to it becoming a major topic of research these days due to improvement in cryosurgery (Ge et al. 2015), heat therapy (Shih et al. 2006; Chen et al. 2018; Tucci et al. 2021, 2022), and thermal detection of diseases (Shi et al. 2014). Heat treatment procedures like microwave ablation (MWA), radiofrequency ablation (RFA), and high intensity focused ultrasound ablation (HIFU) uses microwave, radio frequency waves, and ultrasound waves to heat the probe, which is inserted into the infected site, to destroy the tumor cells by elevating the temperature of the probe tip greater than cell necrosis temperature (>46 °C). From literature (Pillai et al. 2015), it is being reported that size of ablation during the above mentioned heat therapy process is regulated by blood flow near the infected site. So, the cooling effect produced by blood flow near ablation region can disturb the desired temperature of infected tissues during the heat therapies which can lead to recurrence of tumor cells. Because of this, prediction of temperature field in tissues during these therapies is important to achieve cell necrosis of infected tissues and minimal damages to healthy tissues (Lee et al. 2018). Thermal ablation works on the principle of elevated tissue temperature (Hyperthermia) or depressed tissue temperature (Hypothermia) of infected tissues to produce cellular necrosis. Temperature change is concentrated on a very small tissue area as a slight miscalculation can destroy healthy cells (Brace 2011; Andreozzi et al. 2019). Due to presence of blood vessels near the target sites, full cell necrosis cannot be achieved and blood vessels have been linked to sites of recurrence. Because of the enhanced requirement of oxygen and nutrients, tumor cells reprogram the blood vessels to form a network near the infected site which is known as epithelial to mesenchymal transition (EMT) (Kalluri and Weinberg 2009).