Quantifying the effect of biopsy lateral decubitus patient positioning compared to supine prostate magnetic resonance image scanning on prostate translocation and distortion.

INTRODUCTION

More than a quarter of tumors are missed by magnetic resonance imaging/ultrasound (MRI/US) fusion-guided biopsy, the majority due to software-based misregistration. Transrectal approaches to biopsy are typically performed in the lateral decubitus position; conversely, diagnostic MRI is performed with the patient lying supine. Any position-related difference in prostate location or gland deformation could potentially exacerbate misregistration at subsequent biopsy.

METHODS

Fifteen healthy male volunteers (mean age 35.9 years, range 27-53) were included in this prospective, institutional review board-approved study. Each volunteer had an MRI performed in the supine position, followed by the second in the lateral decubitus position (mimicking a typical biopsy position). MRI images were co-registered and analyzed in order to assess prostate translocation and distortion.

RESULTS

Whole prostate translocation of ≥5 mm was observed in 20% of patients and of ≥3 mm in 60% of patients. When dividing the prostate into prostatic sectors, the prostatic base demonstrated the largest positional difference. When plotting the translocation directions with relative volume difference, there was a moderate negative correlation trend in the latero-lateral direction. Only minimal distortion was observed, with similar distortion among all prostatic sectors.

CONCLUSIONS

Positional change affects the prostate translocation, however, the effect on prostate distortion appears to be negligible. Prostate translocation in latero-lateral direction can be minimized with larger bladder volumes. Prostate translocation needs to be considered alongside software misregistration error; however, positional change should not affect software registration of MRI/US fusion-guided prostate biopsy.