High-intensity focused ultrasound (HIFU) is a non-invasive treatment that uses focused ultrasound energy to heat and destroy tissue. HIFU is sometimes referred to as focused ultrasound ablation. It has emerged as an effective and safe modality for tumor ablation in a variety of tissues. HIFU is being applied clinically for the treatment of tumors in the prostate, breast, liver, kidney, pancreas, bone, and soft tissue.
The number of HIFU treatments needed depends on several factors, including:
- Type of tumor being treated
- Size of tumor
- Location of tumor
- Individual response to HIFU
In general, most patients require between 1-3 treatments to fully ablate a tumor. However, some may need additional treatments depending on their unique clinical situation. The number and frequency of treatments is tailored for each patient.
How Does HIFU Work?
HIFU uses focused ultrasound energy generated by a specialized transducer to heat tissue to 60-100°C. This causes cellular necrosis and protein denaturation in the targeted tissue while sparing overlaying and surrounding tissue.
The ultrasound beam can focus energy at a small spot deep in the body without causing damage to the tissue it passes through. The beam penetrates through the intact skin and soft tissues and can be targeted to the tumor location with millimeter precision.
The focused ultrasound beam raises the temperature rapidly, and the tissue is heated in a few seconds. A single sonication of the HIFU beam lasts from 1-4 seconds. By scanning the beam, the HIFU transducer can treat the entire targeted volume.
Advantages of HIFU
HIFU offers several advantages over traditional tumor ablation techniques:
- Non-invasive and targeted – No incisions are needed and only the tumor is treated.
- Precise – Using advanced imaging for guidance, HIFU can specifically target the tumor.
- Effective – High rates of complete tumor ablation have been reported.
- Repeat treatments – HIFU allows for repeat treatments if needed.
- Low complication rates – The safety profile is excellent with minimal side effects.
- Outpatient – HIFU can be performed on an outpatient basis.
- Fast recovery – Most patients quickly return to normal activities.
These benefits make HIFU an appealing option compared to surgery or radiation therapy. The non-invasive nature and ability to retreat tumors are significant advantages of HIFU.
What Types of Tumors can be Treated with HIFU?
HIFU has been studied most extensively for the following types of tumors:
Prostate Cancer
HIFU is approved in many countries for prostate tissue ablation, including primary prostate cancer and recurrent prostate cancer after radiation therapy.
It is performed as a day surgery procedure under general anesthesia or spinal anesthesia. Using transrectal imaging, the prostate tumor is targeted precisely. Patients typically go home the same day with a catheter.
Clinical trials have shown HIFU is effective for eradicating prostate cancer while reducing side effects. Up to 95% of patients have been shown to have no detectable prostate cancer after HIFU ablation.
Breast Cancer
HIFU is currently under investigation for non-invasive ablation of breast cancer. It can be used to target breast tumors including ductal carcinoma in situ (DCIS).
Breast HIFU is done under sedation or local anesthesia. The treatment takes about 1-2 hours. Most patients can go home the same day. Mild swelling and bruising can occur which resolves in 1-2 weeks.
Studies have found HIFU for breast cancer has few complications and is effective at destroying breast tumor tissue. Complete necrosis of the treated area is achieved in over 90% of patients. Additional clinical trials are underway.
Liver Cancer
For primary and metastatic liver tumors, HIFU ablation is a promising treatment technique. HIFU can be used to target tumors of the liver safely without harming normal liver tissue.
Liver cancer HIFU is performed under ultrasound image guidance. Probe movement allows the ultrasound beam to sweep across the tumor to achieve ablation. Patients are given light sedation but can go home the same day.
Clinical research indicates HIFU can effectively treat liver tumors less than 5 cm in diameter. Larger lesions can be divided into multiple treatment zones. Response rates up to 90% have been achieved.
Kidney Cancer
Small kidney cancers can potentially be treated with HIFU ablation. The focused ultrasound beam targets the renal tumor while sparing healthy kidney tissue.
The patient lies prone, and the tumor is identified using 3D imaging. The treatment takes approximately 2-3 hours. Patients can usually leave the hospital after a one night stay.
Studies show that HIFU for kidney cancer results in high rates of histologic necrosis of the treated tumors. Up to a 97% response rate has been seen. HIFU could be a viable minimally invasive option compared to partial nephrectomy.
Pancreatic Cancer
Locally advanced and metastatic pancreatic cancer can cause debilitating pain. HIFU therapy has been shown to relieve pain and improve quality of life in these patients.
By precisely targeting the nerves surrounding the pancreas, HIFU can provide effective pain palliation in 80-90% of patients. The effect can be long-lasting. Repeat sessions can be performed for recurrent pain.
For patients with unresectable pancreatic cancer causing severe pain, HIFU can offer a non-invasive alternative to narcotics and surgery. Clinical trials are ongoing.
Bone Cancer
For bone metastases, HIFU ablation can relieve pain and reduce skeletal complications. It provides an option for palliative treatment of painful bone lesions.
MR-guided HIFU can precisely target metastases in weight-bearing bones. Treatment takes approximately 1-3 hours depending on the size and location. Pain relief can be immediate and last for many months.
In studies, significant improvements in pain scores, reduced opioid use, and better quality of life have been demonstrated with bone cancer HIFU treatment. It has become an important palliative therapy option.
How is HIFU Guidance Performed?
Accurate image-guidance is critical for delivering HIFU therapy. Advanced 3D imaging is used to plan each patient’s unique HIFU treatment and provides real-time imaging during the procedure.
There are two main image-guidance techniques used for HIFU:
Ultrasound Guidance
Ultrasound imaging uses sound waves to see structures inside the body. For HIFU, transducers are integrated into the table patients lie on (HIFU devices designed for the prostate or breast). This allows ultrasound imaging of the treatment area.
During the procedure, ultrasound provides rapid, detailed imaging showing the anatomical structures, tumor location, and surrounding healthy tissue. This allows precise HIFU beam targeting and monitoring of the ablation.
MRI Guidance
Magnetic resonance imaging (MRI) uses radio waves and magnets to create detailed 3D images. It can accurately visualize soft tissue structures, making it well-suited for HIFU guidance.
Specialized HIFU devices are designed to work inside an MRI scanner. This provides exceptional visualization of the tumor and real-time thermal imaging during treatment.
MRI thermometry maps the temperature in the tissues during HIFU ablation. This allows the doctor to precisely control the delivery of ultrasound energy and ensure adequate heating of the entire tumor.
How Many HIFU Treatments are Needed?
The number of treatments required depends on the type, size, and location of the tumor. Some key factors affecting HIFU sessions needed include:
Type of Tumor
Some tumors like liver metastases may be small in size and only require one session. Others like prostate cancer often need 1-2 treatments to fully ablate all cancerous tissue. Pancreatic cancer for pain relief can require several sessions.
Size of Tumor
For larger tumors, multiple treatments may be planned with the sessions spaced weeks apart. This allows adequate cooling between treatments. Smaller tumors (< 2 cm) can generally be treated in one session.
Location
Accessible tumor locations like the breast or prostate make targeting easier and faster. Just 1-2 treatments are usually sufficient. Tumors surrounded by vulnerable structures (bones, nerves, etc) require more precise planning and targeting which may necessitate multiple treatments.
Treatment Goals
The purpose of treatment also affects sessions required. For cancer ablation, the goal is complete tumor destruction so additional treatments may be needed to eliminate residual viable tissue. For pain relief, several sessions are often planned to prolong the effect.
Individual Variability
Patient anatomy, tumor characteristics, and treatment tolerability vary. The HIFU doctor determines the number and timing of treatments based on the patient’s unique scenario and response. This results in customized therapy.
| Tumor Type | Average HIFU Treatments Needed |
|---|---|
| Prostate Cancer | 1-2 |
| Liver Cancer | 1-3 |
| Breast Cancer | 1 |
| Kidney Cancer | 1 |
| Pancreatic Cancer (for pain relief) | 3-6 |
| Bone Metastases (for pain relief) | 1-5 |
This table gives a general guideline on frequency of HIFU ablation by cancer type. However, each case has unique considerations that will determine total treatments required.
Treatment Intervals for HIFU Therapy
If multiple HIFU sessions are required, they are spaced out over weeks or months. Typical treatment intervals are:
- Prostate cancer – 4-6 weeks between sessions
- Liver tumors – 4-8 weeks between treatments
- Breast cancer – 4-12 weeks between procedures
- Kidney cancer – 4 weeks between sessions
- Pancreatic cancer – 4-8 weeks between treatments
- Bone metastases – 8-12 weeks between treatments
Allowing adequate time between HIFU ablation treatments ensures proper cooling of the tissue and minimizes risk of thermal injury. This spacing reduces complications.
Some patients may be brought back sooner based on concerning imaging findings or return of symptoms. Repeat sessions can assess the response to therapy and target any residual tumor as needed.
How is Response Assessed After HIFU Treatment?
Imaging and biomarkers are used to evaluate each patient’s response after undergoing HIFU ablation sessions. This helps determine if additional treatment is required. Monitoring may include:
Follow-up Imaging
MRI, CT scans, PET scans and ultrasound are used to visualize the treatment area. This demonstrates the extent of ablation achieved and any residual tumor. Imaging is done at periodic intervals after HIFU.
Blood Tests
Tumor markers in the blood can be measured when applicable. For example, the PSA level is monitored after prostate cancer HIFU treatment. A declining PSA indicates a good response.
Biopsy
For some cancers, biopsy of the ablated area may be done after HIFU ablation. This provides pathological evidence of tumor destruction.
Symptom Assessment
Relief of tumor-related symptoms is an important indicator of treatment efficacy. Resolution of pain is a positive sign after HIFU for bone metastases or pancreatic cancer.
Quality of Life
Questionnaires measuring functional status, physical health, mood, etc can identify benefits experienced after HIFU therapy for cancer patients regarding pain, energy, mobility and emotional wellbeing.
Conclusion
The number of HIFU ablation treatments required is variable but often 1-3 sessions are sufficient for cancer therapy. The treating physician tailors the regimen based on tumor type, size, location and other factors. Allowing adequate cooling intervals between repeat HIFU treatments reduces risks.
Response is monitored with imaging, biomarkers, biopsy results, symptoms, and quality of life assessments. This comprehensive follow-up determines if additional therapy is warranted. HIFU is a safe, non-invasive ablation technique that can be repeated as needed for optimal patient outcomes.
