MRI, Ultrasound Fusion Helps Target Tumors for Treatment

Fusing the technologies of magnetic resonance imaging (MRI) and ultrasound (US) may help to better target treatment for prostate cancer, according to study published recently in BJU International.

Louise Dickinson, MRCS, and colleagues from the University College London developed new, computer-assisted deformable MR-US registration software that fuses three-dimensional, multiparametric MRI-derived information on lesion location onto the ultrasound images obtained by the Sonablate 500 high-intensity focused ultrasound therapy device. When the software was tested in this study, it was found to be clinically feasible and efficient.

“The use of MR-US registration potentially provides a cost-effective solution for visualization and targeting of clinically significant cancers that, as shown in this study, can be easily integrated within existing workflows and interfaces, using standard surgical equipment,” Dickinson told Diagnostic Imaging.

According to Dickinson, there is increasing interest in tissue-sparing treatment of localized prostate cancer, in which the dominant and clinically significant cancer is treated. With accurate characterization and localization of the tumors, the potential benefit of tissue-sparing treatment is sparing the surrounding normal tissue, and minimizing collateral damage, with the aim of preserving genitourinary function.

“Multiparametric MRI is currently the most accurate tool for this purpose,” Dickinson, said. “However, as ultrasound is the main platform for guiding the delivery of the majority of ablative treatments, and cancer lesions normally cannot be seen on ultrasound, a system is required that transfers, or fuses, the MRI information on tumor location and size onto the ultrasound images displayed by the device.”

In their study, the researchers evaluated this new software on 26 consecutive men nested within the larger INDEX study. All participants had manual contouring of the prostate capsule and histologically confirmed MR-visible lesion performed by a urologist and uro-radiologist. Using patient-specific tumor models, the location of the lesion was generated and transferred to a three-dimensional transrectal ultrasonography (TRUS) volume using capsule points. During the high-intensity focused ultrasound the operator could add treatment volume, but not subtract it.

Results of the study indicated that prostate capsule and lesion contouring was achieved in less than five minutes preoperatively. The mean time to register images was six minutes when the researchers measured the time that the TRUS volume was transferred to a separate workstation and then run through the new software. Half of patients had additional treatment margins added.

“An MR-US registration system such as this may allow improved accuracy for localizing lesions and delivering focal treatments, ensuring that margins of the lesion are covered, whilst avoiding over-treatment of surrounding normal tissue,” Dickinson said. “Furthermore, accurate MR-US registration also has implications in the diagnostic pathway for prostate cancer, whereby biopsies can be targeted to clinically significant lesions visualized on ultrasound biopsy platforms, for more efficient tissue sampling and risk stratification.”

According to Dickinson, further work is now required to formally evaluate the clinical impact of image-directed, tissue-preserving prostate cancer therapy in terms of patient outcomes, within prospective clinical studies.