System for prostate brachytherapy and biopsy in a standard 1.5 T MRI scanner

Abstract

A technique for transperineal high-dose-rate (HDR) prostate brachytherapy and needle biopsy in a standard 1.5 T MRI scanner is demonstrated. In each of eight procedures (in four patients with intermediate to high risk localized prostate cancer), four MRI-guided transperineal prostate biopsies were obtained followed by placement of 14-15 hollow transperineal catheters for HDR brachytherapy. Mean needle-placement accuracy was 2.1 mm, 95% of needle-placement errors were less than 4.0 mm, and the maximum needle-placement error was 4.4 mm. In addition to guiding the placement of biopsy needles and brachytherapy catheters, MR images were also used for brachytherapy treatment planning and optimization. Because 1.5 T MR images are directly acquired during the interventional procedure, dependence on deformable registration is reduced and online image quality is maximized.

FIG. 1

Needle placement and imaging device. a: The needle-guiding template is fixed at a right angle to the endorectal imaging coil. After positioning, both are fixed in place with an immobilization arm. b: The template holes, filled with surgical lubricant, are easily visualized in MR images. c: After registration of the position and orientation of the needle-guiding template, colored dots (representing the path of each needle hole) are projected through the image volume. Visualization of the template allows for easy verification of this registration.

FIG. 2

Needle placement accuracy histogram and maximum-likelihood Rayleigh distribution. Needle location errors (distance, measured in the axial plane, between the needle void and the intended target site) for the 32 biopsy needle placements. The mean placement error was 2.1 mm (error distribution is modeled by a Rayleigh distribution with a sigma value of 1.6 mm).

FIG. 3

High-dose-rate (HDR) brachytherapy catheter placement and isodose maps. At the beginning (a) and end (b) of a 5-week course of external beam radiation therapy, HDR brachytherapy was performed using catheters placed under MRI guidance (both images are from the same patient). c,d: Radiation isodose maps, corresponding to a,b, indicate 150% (red contour), 125% (orange contour), 100% (green contour), and 75% (blue contour) of the prescribed radiation dose (1050 cGy). The prostate (gray filled region), urethra (white region inside the prostate), and rectum (hatched region) are also shown. Note that the green, 100% dose contour conforms well to the prostate margin, while overdose of the urethra and rectum is avoided.