Definition & Overview
High intensity focused ultrasound (HIFU) is an emerging form of non-invasive therapy for tumour ablation. While ultrasound was previously used for diagnostic imaging, advancements in ultrasound technology now allow the use of high intensity focused ultrasound energy for treatment purposes due to its ability to cause tissue ablation and hemostasis. As an emerging form of treatment, its effectiveness in treating primary and metastatic tumours and in encouraging hemostasis in traumatic injuries is still evolving. Ultrasound’s ability to reach the deep layers of tissues within the body makes it a unique tool for non-invasive therapy, and its ability to cause practically instantaneous yet precise cell death through coagulation necrosis makes it invaluable as a potential cancer treatment.
The use of ultrasound technology for treatment has been studied as early as 1954. In the 1980s, ESWL or extracorporeal shockwave lithotripsy was developed as the first form of high-intensity ultrasound therapy. From there, the technology was further developed in the 1990s. However, despite substantial advancements, the technology is still associated with a number of significant drawbacks that should be taken into consideration by patients.
Who Should Undergo and Expected Results
Patients who can potentially benefit from high intensity focused ultrasound are those who suffer from:
- Primary solid malignant tumours in various organs of the body
- Metastatic tumours
- Internal injuries
- Traumatic injuries
- Uterine fibroids
- Soft-tissue sarcomas
HIFU has been used in the treatment of tumours in the:
Currently, cancer treatment such as open surgery, radiotherapy, and chemotherapy are unable to duplicate the unique advantages of HIFU, which include:
- Completely non-invasiveness
- Minimal pain
- No scarring
- Lower risk of complications and systemic side effects
- Shorter recovery periods (compared to surgical methods)
- Shorter hospital stays
- Lower risk of damaging nearby tissues, such as blood vessels in close proximity to the diseased tissues (a major risk in surgical resection)
- Minimal bleeding (as ultrasound can stop bleeding if it occurs)
- Reduced toxicity (compared with other ablation techniques including cryotherapy)
- Higher size limit of 3 to 4 cm in diameter for treatable tumours (compared to other minimally invasive treatments)
- No dose limit (which means the treatment can be repeated if necessary)
The therapy works by delivering the required level or intensity of energy to heat up the tissue to a cytotoxic level to destroy the cancerous tissue. It then encourages hemostasis to induce healing. The high-intensity focused ultrasound easily passes through healthy skin and tissue without causing any unnecessary harm. The energy is only delivered when the ultrasound is focused specifically and precisely on the tumour, regardless of how deep within the body it is. The technology is also useful for mediated drug delivery directly into the affected tissues, as well as for vessel occlusion and soft tissue erosion or histotripsy.
With the neurotoxic side effects of chemotherapy and other leading cancer therapies, the use of high intensity focused ultrasound, which is better tolerated by patients, can significantly advance cancer treatment.
So far, the technology has been used in more than a hundred thousand cases all over the world, with positive results.
How is the Procedure Performed?
High intensity focused ultrasound can be performed on an outpatient basis without the use of sedation or any type of anaesthesia. It involves inserting an ultrasound probe into the rectum and focusing high-intensity beams of ultrasound energy on the cancerous tissues.
The ultrasound energy then heats the cancerous tissue up to 60 degrees Celsius or higher. This causes instant coagulation necrosis, even when the energy is focused for just 1 second. Since the energy is focused on the affected tissues, thermal damage to nearby tissues and the overlying tissues in between the transducer and the targeted tissue can be avoided.
The use of high-intensity energy also brings about some effects that do not occur with low-intensity energy. These include:
- Radiation forces
After the procedure, patients do not suffer from painful incision wounds or severe side effects similar to those felt after chemotherapy. Thus, most of them can go home on the same day.
Possible Risks and Complications
Studies show that although HIFU is effective in treating cancer, it does not prevent future cancer growth. Unpublished research showed that one in three cases of prostate cancer patients treated with HIFU developed cancer again two years after their treatment.
Although safer than other existing cancer treatment options, HIFU is also not without its fair share of risks. Potential side effects linked to the procedure include:
- Erectile dysfunction
- Urinary retention
All existing drawbacks of ultrasound therapy, such as refraction, reverberation, and acoustic shadowing, also apply to HIFU.
Although these disadvantages do nothing to deny the fact that HIFU is indeed effective, they also make it clear that great care has to be taken in performing the procedure to prevent adverse effects and that there is no guarantee that cancer will not recur once treated with high intensity focused ultrasound.
Dubinsky TJ, Cuevas C, Dighe MK, Kolokythas O, Hwang JH. “High-intensity focused ultrasound: Current potential and oncologic applications.” American Journal of Roentgenology. 2008. January; 190(1). http://www.ajronline.org/doi/full/10.2214/AJR.07.2671
Schieszer J. “Caution urged with high intensity focused ultrasound therapy in prostate cancer.” 2015 December 30. http://www.cancertherapyadvisor.com/prostate-cancer/prostate-cancer-pca-high-intensity-focused-ultrasound-therapy/article/462389/