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Abstract Summary: One of the medical field’s aspirations is to provide patients with minimally invasive therapy. With such therapy, infection and blood loss is minimized, procedure and recovery time is shortened, and procedures can be offered on an outpatient basis. HIFU is an extracorporeal non invasive method for tumor ablation. Ultrasound beam can travel through the body and reach area of targeted tissue which is deep within the body. Focusing this beam makes the acoustic energy at the focal region much higher compared with the region outside the focus. As a result, the energy deposition in the tissue along the US beam path which locates outside the focal region is so low that be difficult to induce the tissue damage. Accordingly, the tissues including tumors at the focal region would absorb enough energy of US beam causing heat generation and inducing tissues damage by producing coagulation necrosis if the temperature in the tissue is raised to 60°C or higher for 1 second or longer. Cooling intervals are needed between each sonication so that the tissue anterior and, to a lesser extent, posterior to the focal spot cool between sonications, allowing further sonications to be placed closer to the first one without any damage to the intervening tissues. Advanced imaging modalities as MRI, US and elasticity imaging make the potential of HIFU for clinical use greatly enhanced by combining HIFU treatment with imaging guidance allowing accurate HIFU dose delivery to the target tissue with minimal damage to the surrounding normal tissue and to evaluate the tissue response to HIFU treatment. HIFU is approved for treatment of many solid tumors. Transrectal HIFU ablation has become a reasonable option for the treatment of localized prostate cancer in non-surgical patients, with 5-year disease-free survival similar to that of radiation therapy. It is also a promising salvage therapy of local recurrence after radiation therapy. HIFU is performed as an outpatient procedure, usually under epidural anesthesia. Several studies have indicated that HIFU treatment and magnetic resonance– guided focused ultrasound surgery (MRgFUS) are safe, effective, and feasible in clinical applications for treatment of uterine fibroids. MRgFUS allows a patient to return to normal everyday life 1–2 days after treatment. When compared with hysterectomy (which reports a 6 to 8 week return), or uterine artery embolization (8 days after which patients return to normal activity). HIFU has the potential of eliminating the invasiveness of current ablative treatment of hepatic masses and the complications of placing needles and probes into an oftentimes more widely diseased liver. It is reported that HIFU can achieve complete tumor necrosis even when the lesion is located adjacent to the major hepatic blood vessels. The main advantage of HIFU over other conventional thermal ablation techniques such as RFA is that it does not require puncturing the tumor, thereby avoiding the risk of bleeding or seeding of tumor cells along the needle tract HIFU ablation of renal tumors in humans remains in the early stages of clinical trials. In brain two mechanisms underlying HIFU-induced cell destruction were proposed: direct effect by ultrasound and indirect effect by drugs delivered through ultrasound-modified blood-brain barrier. In breast cancer using HIFU treatment is attempting to try to replace conventional surgery with a completely noninvasive procedure maintaining efficacy and reducing the cosmetic impact of surgery with allowing patients to have an outpatient treatment. HIFU insonation in bone rapidly heats the targeted bone cortex, and subsequently the adjacent periosteum and the tumor tissue. In addition, the high absorption and the low conductivity of bone tissue lead to a localized effect within the targeted ultrasound beam. HIFU ablation results in fewer complications and well-preserved limb function because there were no surgical traumas and blood vessels > 2 mm in diameter were retained, which could be beneficial to revascularization and the repair of inactivated tumor bones. Because of most of the patients with pancreatic cancer are not suitable for surgery when the diagnosis is made therefore HIFU ablation may be used to extend the life expectancy and improve the quality of life. HIFU treatment of pancreatic tumors indeed relieves pancreatic adenocarcinoma- related pain and focally ablates malignant tissue. |