Abstract

Evaluate whether a decrease in apparent diffusion coefficient (ADC), associated with loss of tissue viability (LOTV), can be observed during the course of thermal ablation of the prostate. Thermal ablation was performed in a healthy in vivo canine prostate model (N = 2, ages: 5 yr healthy, mixed breed, weights: 13-14 kg) using a transurethral high-intensity ultrasound catheter and was monitored using a strategy that interleaves diffusion weighted images and gradient-echo images. The two sequences were used to measure ADC and changes in temperature during the treatment. Changes in temperature were used to compute expected changes in ADC. The difference between expected and measured ADC, ADCDIFF, was analyzed in regions ranging from moderate hyperthermia to heat fixation. A receiver operator characteristic (ROC) curve analysis was used to select a threshold of detection of LOTV. Time of threshold activation, tLOTV, was compared with time to reach CEM43 = 240, tDOSE. The observed relationship between temperature and ADC in vivo (2.2%/ °C, 1.94%-2.47%/ °C 95% confidence interval) was not significantly different than the previously reported value of 2.4%/ °C in phantom. ADCDIFF changes after correction for temperature showed a mean decrease of 25% in ADC 60 min post-treatment in regions where sufficient thermal dose (CEM43 > 240) was achieved. Following our ROC analysis, a threshold of 2.25% decrease in ADCDIFF for three consecutive time points was chosen as an indicator of LOTV. The ADCDIFF was found to decrease quickly (1-2 min) after reaching CEM43 = 240 in regions associated with heat fixation and more slowly (10-20 min) in regions that received slower heating. Simultaneous monitoring of ADC and temperature during treatment might allow for a more complete tissue viability assessment of ablative thermal treatments in the prostate. ADCDIFF decreases during the course of treatment may be interpreted as loss of tissue viability.

Highlights

  • Prostate cancer continues to be the most common type of cancer found in American males

  • Three example ROIs were chosen from regions of interest that reached sublethal (CEM43 = 0), marginal (CEM43 = 494), and highly lethal (CEM43 = 106) thermal dose

  • The tLOTV for this ROI occurs at approximately 30 min, while tDOSE occurs around 15 min

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Summary

Introduction

Prostate cancer continues to be the most common type of cancer found in American males. Benign prostate hyperplasia (BPH) affects more than 50% of men over the age of 601 and leads to urinary incontinence and a decreased quality of life. Invasive therapies based on heatinginduced coagulative necrosis have been developed to help treat patients with these conditions. The heating is intended to destroy the tumor, whereas in BPH, healthy tissue is destroyed in order to relieve pressure on the urethra. MRI has emerged as a promising modality to monitor these treatments due to its ability to noninvasively measure temperature changes during treatment, as well as its flexible contrast modalities for treatment planning and evaluation.. Thermal dose monitoring is used to determine whether a tissue has been exposed to enough thermal energy to undergo coagulative necrosis..

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