Overcoming pubic arch interference in prostate brachytherapy using steerable needles.

Purpose: A proportion of patients are not directly eligible for prostate brachytherapy (BT) due to pubic arch interference (PAI). Constraints in positioning sources behind the pubic arch due to linear, horizontal needle paths, may hamper effective irradiation of the target volume. This work evaluated the effect of prostate volume (V_p) and patient posture change on the amount of PAI, and demonstrated that steerable needles may broaden the inclusion criteria for patients with enlarged prostates and observed PAI.

Material and methods: Twenty-seven patients (V_p > 60 cc) were included in this study. Access obstruction to the prostate was evaluated using diagnostic magnetic resonance imaging (MRI) scans, after six upward rotations of the pelvis and the prostate in 5 degree steps, to indicate the effect of patient posture change from supine to lithotomy position. For patients with PAI, we evaluated if the steerable needle could access the obstructed volume of the prostate.

Results: The data showed no clear relation between V_p and PAI. In 23 of the 27 patients, in which PAI was observed, 14 showed obstruction of the prostate of ≥ 10 mm in the supine position (mean PAI ± standard deviation: 15.2 ±3.8 mm). Anatomical rotation reduced PAI by 4.8 mm after every 10 degrees of upward rotation, still resulting in obstructions of 8.1 ±2.4 mm in 10 of the 14 cases after 15 degree rotation. The steerable needle enabled access to all the required coordinates of the prostate.

Conclusions: The ability to steer along curved paths enables prostate BT in patients with enlarged prostates and PAI, and reduces the change of needing to abandon treatment.