Analysis of the spatial and temporal accuracy of heating in the prostate gland using transurethral ultrasound therapy and active MR temperature feedback

Abstract

A new MRI-guided therapy is being developed as a minimally invasive treatment for localized prostate cancer utilizing high-intensity ultrasound energy to generate a precise region of thermal coagulation within the prostate gland. The purpose of this study was to evaluate in vivo the capability to produce a spatial heating pattern in the prostate that accurately matched the shape of a target region using transurethral ultrasound heating and active MR temperature feedback. Experiments were performed in a canine model (n = 9) in a 1.5 T MR imager using a prototype device comprising a single planar transducer operated under rotational control. The spatial temperature distribution, measured every 5 s with MR thermometry, was used to adjust the acoustic power and rotation rate in order to achieve a temperature of 55 degrees C along the outer boundary of the target region. The results demonstrated the capability to produce accurate spatial heating patterns within the prostate gland. An average temperature of 56.2 +/- 0.6 degrees C was measured along the outer boundary of the target region across all experiments in this study. The average spatial error between the target boundary and the 55 degrees C isotherm was 0.8 +/- 0.7 mm (-0.2 to 3.2 mm), and the overall treatment time was < or =20 min for all experiments. Excellent spatial agreement was observed between the temperature information acquired with MRI and the pattern of thermal damage measured on H&E-stained tissue sections. This study demonstrates the benefit of adaptive energy delivery using active MR temperature feedback, and an excellent capability to treat precise regions within the prostate gland with this technology.

Fat‐referenced MR thermometry in the breast and prostate using IDEAL

“…MR THERMOMETRY IS increasingly used to guide and monitor thermotherapy procedures for cancer treatment. These procedures include focused ultrasound (FUS) ablation (1)(2)(3)(4), radiofrequency (RF) ablation (5), laser ablation (6,7), and mild adjuvant RF hyperthermia (RF-HT) (8)(9)(10). These relatively noninvasive procedures require accurate and fast estimates of temperature and thermal dose over a region to ensure maximal damage to the diseased tissue, while sparing surrounding healthy tissue from inadvertent damage.…”

“…For the porcine tissue and prostate experiments, the correction map was computed using a second-order polynomial in Eq. [4]. For the breast imaging experiment, the correction maps were computed using a second-, third-, and fourth-order polynomial fit.…”

Magnetic Resonance Image Guided Transurethral Ultrasound Prostate Ablation: A Preclinical Safety and Feasibility Study with 28-Day Followup

“…12 Previous in vivo canine studies demonstrated the capability of generating thermal patterns that conform to predetermined target volumes 13e17 with 1 to 2 mm accuracy and precision. 14,15 Comprehensive histological analysis revealed the close relationship between acute 100% cell kill and a critical temperature threshold of 55C (on the order of 1 mm), and the peripheral region of enhancement surrounding the NPV on CE-MRI immediately after treatment (on the order of 3 mm). 14,15,18 Delayed cell kill at 48 hours migrated 1 to 3 mm beyond the acute cell kill volume.…”

Prostate cancer - the role of magnetic resonance imaging

“…Another form is MRI-guided percutaneous interstitial microwave thermoablation in locally recurrent tumor. Chopra et al showed that using MRI thermometry while applying transurethral MRI guided high intensity-focused ultrasound (HIFU) allowed for stable temperature measurements 18 to avoid thermal damage of surrounding tissues during the intervention. T2-weighted imaging/DCE-MRI is a promising method for guiding post-HIFU biopsy towards areas containing residual (benign or malignant) viable prostate tissue and to sensitise the detection of locally recurrent cancer in patients with biochemical recurrence.…”