Therapeutic Ultrasound and Prostate Cancer

Abstract

Therapeutic ultrasound approaches including high-intensity focused ultrasound (HIFU) are emerging as popular minimally invasive alternative treatments for localized, low-to-intermediate risk prostate cancer. FDA approval was recently granted for two ultrasound-guided HIFU devices. Clinical trials for devices using MRI guidance are ongoing. The current level of evidence for whole-gland ultrasound ablation suggests that its clinical efficacy and adverse event rates including erectile dysfunction and urinary incontinence are similar to current definitive therapies such as radical prostatectomy and external-beam radiotherapy. Short-term data suggest that more focal therapy could reduce the rates of adverse events.

Keywords: high-intensity directional ultrasound; high-intensity focused ultrasound; prostate cancer; therapeutic ultrasound.

Figures

Fig. 1

Representation of transurethral and transrectal whole-gland ablation approaches. The transurethral approach, referred to as TULSA, uses continuous heating, whereas the transrectal approach treats the whole gland by targeting discrete lesions encompassing the prostate volume. (Image used with permission from Profound Inc.)

Fig. 2

Currently available therapeutic ultrasound devices. (a) Sonasource with Sonablate and Sonachill. (b) Ablatherm II. (c) Focal One. (d) TULSA-PRO. (e) Exablate. (Images provided by respective manufacturers.)

Fig. 3

Representative focal treatment using the Sonoblate 500 system. (a) Representative MR image showing three lesions in the contoured prostate, with the red lesion representing clinically significant cancer. (b) TRUS image. (c) Fused MR–ultrasound image with lesions superimposed in the ultrasound volume. (d) 3D representation of prostate volume and lesion volumes. (e) Treatment planning images. Blue lines represent the longer focal length transducer (4 cm), which creates lesions of 12 × 3 × 3 mm. The red dots represent the center of 12 mm AP ablation lesions that encompass the high-risk lesion and extend beyond the lesion margin to provide adequate treatment margins. (f) Coronal image showing the red dots encompassing the entire craniocaudal length of the lesion and to the determined safety margin. (g) Green dotted line representing the rectal wall, which is constantly monitored during treatment. (h) Diagram demonstrating energy application from the transducer to the predetermined treatment area. (Image created by combining images provided by Sonacare Medical LLC.)

Fig. 4

Representative sagittal MRI image demonstrating placement of the transurethral ultrasound applicator and the endorectal-cooling device which are a part of the TULSA-PRO system. (Image used with permission from Profound Inc.)

Fig. 5

Thermometry and contrast-enhanced MRI from TULSA-PRO treatment.Top-row:MR thermometry images acquired after treatment completion using the TULSA-PRO device demonstrating the T max reached in every voxel. Please note the urethral cooling as seen by low temperatures around the transurethral device (blue voxels). The temperatures are hottest around the urethra.Bottom-row:Posttreatment gadolinium-enhanced T1W MR images demonstrating the nonperfused volume which is congruent with the temperature maps on the top row.

Fig. 6

Diagrammatic representation of the functionality of the TULSA-PRO device. Inlaid MR images on the top-left corners demonstrate the directional ultrasound beam (represented by the solid red line) extending to the prostate capsule (solid black line). Image (a) demonstrates that treatment starts at 5 o'clock and rotated counter clockwise after delivering the required heat as measured by PRF thermometry in imagesb, c,andd. The color overlay represents Tmax reached in every voxel. The bottom row in each image demonstrates how heating is progressing at other axial slices in the prostate (right to left—base to apex) reaching up to 90°C (purple voxels). Also, we can see that temperatures at the capsule are controlled to 55°C (green voxels). (Image used with permission from Profound Inc.)