In a previous study, prostatic swelling and shift toward the antero-lateral direction were confirmed (1). The majority of swelling (median 13%) and shift (transition zone, median 3.7 mm; peripheral zone, median 5.5 mm) occurred in the initial 25 min during whole gland therapy as a result of diffuse coagulative degeneration and diffuse stromal edema of the prostate (1, 2).
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Therefore, it was considered that intra-operative adjustment of the treatment plan is needed, depending on the amount of prostatic swelling. However, intra-operative tracking of the small target zone during HIFU is difficult because of the blurred ultrasound image affected by HIFU. Therefore, the development of a method to enable precise lesion targeted focal therapy using HIFU is needed.
Previous studies have shown that the prostatic pressure was significantly correlated with the percent increase in prostate volume (r=−0.607; p<0.001) and intra-prostatic point shift (r=−0.433; p=0.01) during HIFU(1). Based on these results, we hypothesized that prostatic swelling and shifts would be reduced in the prostate by high intra-operative prostatic pressure. As a method for increasing intra-prostatic pressure, transrectal compression using a HIFU probe was considered as a simple method. The objective of our study was to evaluate the morphological effects of transrectal compression of the prostate treated with HIFU for localized prostate cancer.
Patients treated with whole-gland HIFU as primary monotherapy for localized prostate cancer were enrolled in the study. Using the standard and compression method, the volumes of degassed water in the balloon covering the HIFU probe were 50 mL and 80–160 mL, respectively. To identify prostatic swelling and shift during HIFU and the volume occupied by the non-enhanced area, three-dimensional prostate models were reconstructed using ultrasound and contrast-enhanced magnetic resonance imaging.
In comparison with the standard (n=40) and compression (n=48) methods, intra-operative increase in the prostate volume (21% vs. 5.3%; p=0.044), intra-prostatic point shift (4 mm vs. 2 mm, p=0.040 in the transition zone; 3 mm vs 0 mm; p=0.001 in the peripheral zone) (Figure) and the volume occupied by the non-enhanced area (89% vs. 96%; p=0.001) were significantly suppressed. The biochemical disease-free survival rate in patients treated using the compression method were significantly improved relative to the standard method (92.6% vs. 76.5%; p=0.038). Regarding complications, there was no significant difference in the rate of urethral stricture (p=0.9), urinary tract infection (p=0.9), incontinence (p=0.3), erectile dysfunction (p=0.9), or recto-urethral fistula between the patients treated using the standard and compression methods.
In conclusion, intra-operative transrectal compression of the prostate significantly suppressed prostatic swelling and shift during HIFU, and has the potential to achieve precise whole gland and lesion-targeted focal therapy.
1. Shoji S, Uchida T, Nakamoto M, et al. Prostate swelling and shift during high intensity focused ultrasound: implication for targeted focal therapy. The Journal of urology. 2013;190(4):1224-32.
2. Shoji S, Tonooka A, Hashimoto A, et al. Time-dependent change of blood flow in the prostate treated with high-intensity focused ultrasound. International journal of urology : official journal of the Japanese Urological Association. 2014;21(9):942-5.
Sunao Shoji M.D., Ph.D.
Associate Professor, Department of Urology, Tokai University School of Medicine, Tokyo, Japan