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Contrast-enhanced ultrasonography for real-time monitoring of interstitial laser thermal therapy in the focal treatment of prostate cancer.

INTRODUCTION
We report a case study of the application of contrast-enhanced ultrasonography (CEUS) for intraoperative monitoring of thermal ablation of a single focus of prostate cancer.


METHODS
A patient presented with biopsy-proven, solitary-focus, low-risk prostate cancer and was recruited into a clinical trial of interstitial laser thermal focal therapy. Multiparametric magnetic resonance imaging (MRI) was used to locate the single dominant focus, and photothermal ablation was performed at the tumour site under the guidance of transrectal ultrasonography. Transrectal CEUS using systemic bolus injections of the intravascular contrast agent Definity was performed immediately before, several times during and on completion of therapy. Lesions observed on CEUS were compared with treatment effect as measured by tissue devascularization on 1-week gadolinium (Gd)-enhanced MRI.


RESULTS
Baseline images showed CEUS contrast-agent signal throughout the prostate. During and after treatment, large hypocontrast regions were observed surrounding the treatment fibres, indicating the presence of an avascular lesion resulting from photothermal therapy. Lesion size was found to increase during the delivery of thermal energy. Lesion size measured using CEUS (16 x 11 mm) was similar to the 7-day lesion measured using Gd-enhanced T(1)-weighted MRI.


CONCLUSION
Focal therapy for prostate cancer requires both complete treatment of the dominant tumour focus and minimal morbidity. The application of CEUS during therapy appears to provide an excellent measure of the actual treatment effect. Hence, it can be used to ensure that the therapy encompasses the whole target but does not extend to surrounding critical structures. Future clinical studies are planned with comparisons of intraoperative CEUS to Gd-enhanced MRI at 7 days and whole-mount pathology samples.