MRI-Guided HIFU Treats Prostate Cancer Without Unwanted Side Effects

Men who have intermediate-risk prostate cancer can be successfully treated with MRI-guided high-intensity focused ultrasound (MRgFUS) without experiencing any significant side effects.

With the use of this combined technique, investigators have found nearly all men were disease-free several months post-treatment and none experienced major treatment-related adverse events.

Surgery and radiation therapy – common prostate cancer treatments – frequently result in incontinence and sexual dysfunction. High-intensity focused ultrasound (HIFU) is a good way to target therapy and avoid negative side effects, it does not give the radiologist a clear enough picture of the cancer site inside the prostate gland to allow for targeted therapy. Consequently, a team of researchers from Canada opted to test whether combining MRI-guidance with HIFU – MRgFUS – would be a more exact approach.

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“By combining the high-intensity focused ultrasound device with MRI, we can target our treatment to the exact location, because we’re able to pinpoint precisely where the tumor is,” said lead author and principal investigator Sangeet Ghai, M.D., deputy chief of research and associate professor at University Health Network Sinai Health and Women’s College Hospital in Toronto.

Ghai’s team initially hypothesized that 70 percent of men would respond well to treatment with no residual clinically significant prostate cancer. Their results, which exceeded their expectations, were published Feb. 2 in Radiology.

To test whether this treatment option provided patients with better results, Ghai’s team enrolled 44 men, who averaged 67-years-old and who had intermediate-risk prostate cancer, between February 2016 and July 2019 into the single-institution study. The men also had prostate-specific antigen (PSA) levels of 20 ng/mL or less and less than 20 mm of MRI-visible grade group 2 or 3 disease at transrectal ultrasound-guided systematic and targeted biopsy.

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After undergoing a 3T MRI for a baseline on all lesions, patients, while under general anesthesia, received treatment with an endorectal focused ultrasound system integrated with a 1.5T scanner that concentrated high-frequency ultrasonic waves of greater than 60-degrees Celsius directly onto the cancer site. Treatments lasted, on average, four hours. Post-treatment, the team tracked the men’s outcomes with MRI, as well as with biopsies and surveys about their urinary and erectile function.

Figure 1: Images in 69-year-old man with biopsy-confirmed Gleason score 7 (3+4) prostate cancer. (a) Pretreatment axial T2-weighted fast spin-echo MRI scan (repetition time msec/echo time msec, 3820/97) shows tumor in midline anterior transition zone (arrow). (b) Intraoperative MRI scan shows contoured rectal wall (red line), prostate margin (blue outline), and region of interest (orange outline). Because the urethra was included in planned treatment volume, a suprapubic catheter was placed for continuous bladder drainage during treatment. (c) Intraoperative MRI scan shows focused ultrasound beam path (blue) overlaid on treatment plan. Green depicts softwaregenerated region of expected heat deposition based on planning. Rectangles illustrate each sonication spot. (d) Thermal map image obtained during treatment with heat deposition color coded in red overlaid on sonication spot. (e) Axial gadopentetate dimeglumine–enhanced MRI scan (230/2.97) obtained immediately after treatment shows devascularized ablated volume (arrows). (f) Corresponding T2-weighted fast spin-echo MRI scan (3820/97) at 5 months after ablation shows complete involution of transition zone. All seven cores from treatment area margins were negative for cancer at biopsy. Courtesy: RSNA

After five months at follow-up, nearly all participants – 93 percent – were disease-free, and none had experienced any major adverse events related to treatment. Only three men had any residual cancer, and the average remaining tumor size was 11 mm. In addition, the group also saw PSA improvement with average baseline levels of 6.4 ng/mL falling to 2.4 ng/mL at five months.

Patient also reported no significant changes in erectile function or in prostate symptoms between baseline and follow-up, the team said.

“The results so far have been very good,” Ghai said, estimating that between 20 percent and 30 percent of men would be eligible for this treatment option. “We treated a smaller area using this device, yet still had very good results. At the same time, the patients preserved their erectile and urinary function.”

The results, the team concluded, compared favorably to ultrasound focal therapy. The performance makes the added expertise, resources, and cost required worth it, they said. Not only can MRI reveal whether the patient has any lingering vascularity in the treatment area – a sign that not all the cancer has been eliminated – but it can also offer real-time thermal feedback.

“MRI almost instantaneously gives feedback as to the temperature that we’ve been able to achieve at the site,” Ghai said. “If the temperature was not what I wanted to get, I can re-heat that area so that chances for successful treatment increase.”

Despite these promising results, however, the study did have a significant shortcoming that leaves many questions unanswered, said Clare M.C. Tempany-Afdhal, M.D., Ferenc A. Jolesz, M.D., professor of radiology at Harvard Medical School and vice chair of radiology at Brigham and Women’s Hospital. Although the study by Ghai’s team was initially intended to multi-institutional, they were unable to recruit enough participants, she said in an accompanying editorial. That shortcoming left three lingering questions:

• Who should be treated – just men with intermediate risk or can low- and high-risk men also be treated with MRgFUS?
• What is the extent of the ablation margin, and how can it best be achieved? Finding the answer will require more accurate MRI-based 3D prostate cancer volumes.
• How does tissue ablation versus tissue preservation relate to post-treatment function? More needs to be learned about how the ablation zone relates to the loss of erectile function, she said.

Even with these questions, she added, Ghai’s team has laid a foundation for larger, multi-center trials that will provide more detail for accurate and greater tumor characterization, such as micro-structural MRI, tumor margin definition, and 3D volume measurement. Ultimately, she said, the goal is to provide better early detection of recurrent or new cancers that are clinically significant.

“This study represents an important step forward in providing a non-invasive treatment for localized prostate cancer,” she said. “For now, the morbidity associated with whole-gland therapies will continue to be present for our patients to achieve a certain control of prostate cancer.”

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