Shape memory alloy (SMA) based active needles [1] have shown the potential to introduce remarkable improvements to many percutaneous needle-based procedures such as thermal ablation, brachytherapy and breast biopsy. Brachytherapy for instance is a common procedure to treat early stage prostate cancer because its superior clinical outcome. Prostate cancer is sex specific and only affects males; it is more prevalent in elderly males, ages 65–74 years old [2]. There is projected to be a 24% increase in cancer cases for men by 2020, this would mean approximately 1 million new cases each year [3]. There was a study in 2015 [4] that examined the needle placement accuracy for brachytherapy procedure while implementing the use of a 3D navigation system, Surgical Planning and Orientation Computer System. The study examined the Target Registration Error (TRE) for single and multiple needle placements. Analysis of the 250 different targets showed a mean Target Registration Error for single needle applications of (1.1 ± 0.4 mm), (0.9 ± 0.3 mm), and (0.7 ± 0.3 mm) in the x, y, and z directions, respectively. The maximum deviation was found 2.3 mm. In another study by Podder et al. [5], the effects of dose distribution has been discussed which has a high influence on the clinical outcome. The study shows that the curvilinear approach by the active needle would introduce the potential for improving dose distribution, reducing number of needles and resulting is better clinical outcome.
Actuating the surgical needles for higher accuracy, SMAs are considered as suitable actuators [6] because of their lightweight, high force and energy density. However, SMA actuated needle will be more complex and may incur additional inaccuracy; thereby after development of a robust active needle, control studies sound very necessary. The focus of this work is to introduce an innovative design of an active needle, and to fabricate the device to demonstrate its capability of creating a high maneuverability at the needle tip. This design of the active needle privileges from actuation of a comparatively long SMA wire to create a considerable amount of deflection, while minimizing the tissue rupture.
Most of the needles today are made of stainless steel, titanium or Nitinol; they are ensured to be sturdy enough to puncture the tissue and overcome its resistance during insertion. This would limit the flexibility of the needles. In our previous designs [7,8], a joint element was included in design to provide more dexterity to the needle’s structure. Despite of the fact that this soft element increased the needle’s flexibility; the design introduced a high tissue rupture during actuation because of the gap between the body of the needle and the SMA actuator. The amount of rupture was increasing with larger deflection of the needle. This work decreases the rupture to a reasonable amount while even a higher deflection compared to our previous design is achieved.
Table 1 lists general specifications and approximations of dimensions and requirements that have been tried to be addressed in the current design as much as possible. There will be still future work to meet some other factors discussed at the end of this study.
Impact of pitch angle setup error and setup error correction on dose distribution in volumetric modulated arc therapy for prostate cancer