Radiology: Ultrasound may offer real-time ablation results

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Contrast-enhanced ultrasound clearly depicts ultrasound ablation of prostate cancer within minutes of the procedure, correlating strongly with biopsy findings and potentially offering interventional radiologists an intraoperative technique to determine whether repeat ablation is necessary, according to a study published in the May issue of Radiology.
Transrectal high-intensity focused ultrasound (HIFU) ablation is used to treat localized prostate cancer as an alternative to surgery as well as to treat recurrences following external beam radiotherapy. At present, however, physicians lack a reliable method for delineating devascularized ablated tissue from nonablated viable tissue, leaving physicians with incomplete information regarding responsiveness to treatment.

“We hypothesized that contrast-enhanced US [ultrasound] with use of the sulfur hexafluoride microbubble contrast agent could depict the volume and position of the treated zone as well as the parts of the gland that were not destroyed,” explained Olivier Rouvière, MD, PhD, and co-authors from Hôpital Edouard Herriot, Hospices Civils de Lyon, in Lyon, France.

Rouvière and colleagues sought to assess the use of contrast-enhanced ultrasound to evaluate the viability and devascularization of tissue following HIFU ablation for prostate cancer. The authors compared ultrasound findings, acquired immediately after ablation, one to three days after treatment and 30 to 45 days after treatment with biopsies taken between 30 and 45 days after ablation.

Twenty-eight patients (median Gleason score 6) underwent HIFU prostate ablation followed by ultrasound at one to three and 30 to 45 days after treatment, as well as biopsy. An additional six patients (median Gleason score 6.5) underwent ultrasound between 15 and 30 minutes after ablation as well as one day after ablation.

Contrast-enhanced ultrasound depicted a large devascularized zone with peripheral enhancing areas (indicating viable tissue) localized anteriorly in all 28 patients on one- to three-day and 30- to 45-day post-ablation ultrasound. Peripheral enhancing areas were also visualized at the apex in 20 patients, posteriorly in nine patients and laterally in five patients. Gadolinium-enhanced MRI agreed with these findings.

Sites to undergo biopsy were classified as S0 for no enhancement on ultrasound, S1 for mild and/or patchy enhancement or S2 for market enhancement. Biopsy revealed viable gland tissue in 6 percent of S0-scored sites, increasing to 34 percent for S1 sites and 60 percent for S2 sites.

Odds ratios for biopsying viable tissue at ultrasound-scored S1 and S2 sites, compared with S0 (unenhanced/devascularized) sites were 21 and 73, respectively. The authors reported similar findings for the 15- to 30-minute and one-day post-ablation ultrasound results.

“In conclusion, contrast-enhanced US clearly depicts HIFU-induced prostate devascularization within minutes after the end of the treatment, and this capability remains unchanged for at least 30 to 45 days. The observed highly significant correlation between post-HIFU contrast-enhanced US and biopsy findings in the ablated prostate suggests that all tissues with enhancement at contrast-enhanced US should be considered to have a high probability of harboring viable tissue,” Rouvière and colleagues wrote.

“Contrast-enhanced US seems to be a promising method for assessing the extent of ablated (devascularized) and viable (enhancing) tissue immediately after HIFU treatment. In the future, this might enable immediate repeat treatment in cases of incomplete tissue destruction.”