Shape analysis of the prostate: Establishing imaging specifications for the design of a transurethral imaging device for prostate brachytherapy guidance

Abstract

Purpose To examine specific prostate and urethra dimensions and prostate shape to facilitate the design of a transurethral ultrasonographic imaging device. Methods and Materials Computed tomographic (CT) data sets were retrospectively evaluated from 191 patients who underwent permanent prostate brachytherapy at our institution. The prostate, rectum, urethra, and bladder were each segmented with imaging software. Collected data and calculations included prostate volume at specific distances from the urethra and rectum, distances from seeds to urethra (SU), distances from seeds to rectum (SR), prostate length, and curvilinear prostatic urethra length. Results CT-based, postimplant mean prostate volume was 49 cm3 (range, 22–106 cm3). Mean prostate length was 4.5 cm (range, 3.1–6.0 cm). The mean curvilinear length of the prostatic urethra was 4.5 cm. The mean (standard deviation) prostatic urethra bend was 29.0° (12.2°). The mean surface distance from the prostate to the urethra was 2.9 cm and from the prostate to the rectum, 4.6 cm (p<.001, paired t test). The mean SU distance was 1.6 cm, and the mean SR distance was 2.3 cm (p<.001). In the largest prostate, the mean SU distance was 3.9 cm and the mean SR distance was 6.0 cm. Conclusions A urethral imaging device for prostate brachytherapy and other minimally invasive prostate therapies should ideally have a 6-cm imaging field of view to image all the prostates in this series in a single image. The mean distance from the urethra to seeds in PPB is less than 70% of the mean seed distance to the rectum.

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