Comparison of transperineal ultrasound image guidance technique to transabdominal technique for prostate radiation therapy.

INTRODUCTION Ultrasound (US) guidance of the prostate has long been conducted using a trans-abdominal (TA) approach. More recently, a transperineal approach (TP) has been made available for image-guidance. Our aim was to determine if both methods produced similar alignments within the same patients. MATERIAL AND METHODS We utilized two clinical US image guidance (IG) systems (Elekta Clarity and Best Bat). The BAT USIG system is a bi-planar, so-called 2.5D USIG system, that is acquired TA. Clarity is a 3D US system that generates a volumetric 3D US data set and US-derived IG contours that are co-registered to the planning CT images. The probe is oriented in the sagittal plane against the perineum (TP). After positioning the patient for treatment using the TP USIG, we maintained the position defined by Clarity tracking and then acquired a TA based USIG. The two US-based methods of localizing the prostate (TA vs TP) were compared via Bland-Altman (BA) statistical analysis to determine if there was alignment agreement between methods. RESULTS The Bland-Altman test for all 101 patients, 2,093 fractions resulted in 95% confidence intervals (upper and lower limits of the Bland-Altman test) of 0.6 mm in LR, 0.9 mm in AP and 1.0 mm in SI. The bias between the two systems was calculated as 0.03, 0.02 and 0.03 mm in LR, AP and SI. CONCLUSIONS Both systems resulted in statistically equivalent targeting positions for the prostate. Because of the unique intra-fraction, real-time motion tracking capability of the TP system, this solution represents a unique extension to the previously reported clinical benefits of a transabdominal approach by providing assurance of the prostate remaining in the treatment field during beam-on.