Brachytherapy needle deflection evaluation and correction

Abstract

In prostate brachytherapy, an 18-gauge needle is used to implant radioactive seeds. This thin needle can be deflected from the preplanned trajectory in the prostate, potentially resulting in a suboptimum dose pattern and at times requiring repeated needle insertion to achieve optimal dosimetry. In this paper, we report on the evaluation of brachytherapy needle deflection and bending in test phantoms and two approaches to overcome the problem. First we tested the relationship between needle deflection and insertion depth as well as whether needle bending occurred. Targeting accuracy was tested by inserting a brachytherapy needle to target 16 points in chicken tissue phantoms. By implanting dummy seeds into chicken tissue phantoms under 3D ultrasound guidance, the overall accuracy of seed implantation was determined. We evaluated methods to overcome brachytherapy needle deflection with three different insertion methods: constant orientation, constant rotation, and orientation reversal at half of the insertion depth. Our results showed that needle deflection is linear with needle insertion depth, and that no noticeable bending occurs with needle insertion into the tissue and agar phantoms. A 3D principal component analysis was performed to obtain the population distribution of needle tip and seed position relative to the target positions. Our results showed that with the constant orientation insertion method, the mean needle targeting error was 2.8 mm and the mean seed implantation error was 2.9 mm. Using the constant rotation and orientation reversal at half insertion depth methods, the deflection error was reduced. The mean needle targeting errors were 0.8 and 1.2 mm for the constant rotation and orientation reversal methods, respectively, and the seed implantation errors were 0.9 and 1.5 mm for constant rotation insertion and orientation reversal methods, respectively.

Robotic assistance for ultrasound-guided prostate brachytherapy

“…They adopted an industrial serial-link robot for needle manipulation while motorizing a conventional TRUS probe to produce a smooth sagittal sweep in the rectum. They were the first to demonstrate synchronized needle and imaging action (in training phantoms) and their results on needle tracking and seed segmentation were particularly exquisite (Wan et al, 2005). Despite its many excellent qualifications, however, to our knowledge this system has not reached human trials.…”

Smooth on-line path planning for needle steering with non-linear constraints

“…Three movement rates, shown in Table I, were considered to demonstrate the ability of the system to reach the target over a variety of displacements magnitudes. These rates were chosen such that the total displacement of the target approximately matches that found in soft tissue procedures [17,18,19]. The direction of the movement of the target is controlled in two primary directions.…”

Robot-Assisted Prostate Brachytherapy

“…In our design process, collection and detailed analysis of this in-vivo information were found to be very useful. It was demonstrated that continuous rotation improved targeting accuracy and reduced insertion force [10], whereas partial rotation increased needle placement accuracy [5]. Therefore, we incorporated the provision for needle rotation in the Euclidean system for improving accuracy and seed delivery.…”

“…In this system, seeds can only be deposited manually. Wei et al [3], [4] and Wan [5] et al developed a robotic system for prostate brachytherapy where they used an industrial robot to position and orient a single hole template through which a needle can be inserted manually. A separate motorized device was developed to rotate the needle and another module used for operating the US probe.…”