Axially rigid steerable needle with compliant active tip control

Abstract

Steerable instruments allow for precise access to deeply-seated targets while sparing sensitive tissues and avoiding anatomical structures. In this study we present a novel omnidirectional steerable instrument for prostate high-dose-rate (HDR) brachytherapy (BT). The instrument utilizes a needle with internal compliant mechanism, which enables distal tip steering through proximal instrument bending while retaining high axial and flexural rigidity. Finite element analysis evaluated the design and the prototype was validated in experiments involving tissue simulants and ex-vivo bovine tissue. Ultrasound (US) images were used to provide visualization and shape-reconstruction of the instrument during the insertions. In the experiments lateral tip steering up to 20 mm was found. Manually controlled active needle tip steering in inhomogeneous tissue simulants and ex-vivo tissue resulted in mean targeting errors of 1.4 mm and 2 mm in 3D position, respectively. The experiments show that steering response of the instrument is history-independent. The results indicate that the endpoint accuracy of the steerable instrument is similar to that of the conventional rigid HDR BT needle while adding the ability to steer along curved paths. Due to the design of the steerable needle sufficient axial and flexural rigidity is preserved to enable puncturing and path control within various heterogeneous tissues. The developed instrument has the potential to overcome problems currently unavoidable with conventional instruments, such as pubic arch interference in HDR BT, without major changes to the clinical workflow.

Overcoming pubic arch interference in prostate brachytherapy using steerable needles

“…If MRI scan length was not sufficient to detect the perineum, the best approximation was made based on the anatomy of patients with sufficient scan length. The maximum amount of PAI defined the upper limit for needle steering, which was compared to the results reported by de Vries et al [23]. In their study, experiments with a novel steerable needle were performed in tissue simulants and ex vivo bovine tissue.…”

“…The change in posture from supine to lithotomy position resulted in improved accessibility of the prostate, but obstructions of more than 5 mm still occurred after 15 degrees of anatomical rotation, which was estimated in literature to relate the supine and lithotomy position [10]. A steerable needle, as presented by de Vries et al [23], may be able to overcome PAI in these cases allowing for the inclusion of patients with enlarged prostates and excessive PAI in prostate BT protocols.…”

“…In the clinical setting, challenges may arise, including the limited workspace for applying steering and real-time imaging of non-straight implant needles in 3D. The novel steerable needle as presented in a study of de Vries et al [23] can overcome PAI, making patients with enlarged prostates and excessive PAI directly suitable for prostate BT without the need for prior hormonal therapy. This spares the patients' the side effects, and the healthcare system the costs related to hormonal therapy.…”

“…The maximum amount of PAI defined the upper limit for needle steering, which was compared to the results reported by de Vries et al . [ 23 ]. In their study, experiments with a novel steerable needle were performed in tissue simulants and ex vivo bovine tissue.…”

“…Steerable needles that enable circumventing of interference from the pubic arch may facilitate proper distribution of the source positions without a change in clinical set-up, and thereby potentially ensure adequate irradiation of the target volume [ 23 ]. Such needles allow for increased flexibility in needle placement, and may extend treatment options for patients with enlarged and obstructed prostates.…”