Novel Pneumatic Device for High Speed Needle Insertion in Brachytherapy

Abstract

Accurate needle placement is important in a number of medical procedures including lumbar puncture, intravenous needle insertion, and percutaneous biopsy. One especially crucial area for precise needle placement and cutting efficiency is in cancer treatment via brachytherapy, wherein needles are used to precisely position small radioactive pellets inside the body. Permanent seed prostate brachytherapy relies heavily on the manual dexterity of medical personnel [1]; thin gauge needles (customarily 18-gauge, 1.27 mm outside diameter) are manually placed within the prostate to position radiation seeds in and around the cancerous prostate tissue [2,3].In prostate brachytherapy, poor needle placement leads to imprecise radiation therapy delivery and ablation of healthy tissue instead of cancerous tissue. Consequently, side effects of the treatment are increased and the patients' quality of life lowered [4]. Low implant quality (seeds misplaced from intended position) is the result of high cutting and frictional forces between the needle and tissue. Tissue deflection displaces the entering needle and the radiation seeds are inaccurately placed, as shown in Figure 1. The malleable and heterogeneous properties of tissue cause it to deform, and due to the reaction to the high needle forces, prostate tissue is especially prone to deflection in terms of splaying and rolling [2,5,6]. Higher velocity tissue cutting has demonstrated decreased tissue deformation [7].Robot-assisted techniques have been investigated to aid medical personnel and improve needle insertion accuracy [8–11], as well as to predict and compensate for tissue deflection. While robot-assisted techniques have significant benefits for medical procedures, they do have several disadvantages to the current methods, including high cost and the difficulty of accurately predicting tissue deflection due to inhomogeneity.This study investigates the effect of percutaneous needle insertion speed on insertion force using a high speed pneumatic device. Determining the optimum insertion speed will ultimately allow for increased needle placement accuracy. This technique could in turn significantly improve percutaneous needle based procedures.A novel pneumatic needle insertion device was developed, depicted in Figure 2. This device utilizes a pneumatic cylinder to propel the needle at high speeds into tissue. The device has a leading handle for stability, a back handle which contains the trigger to launch the needle, and a sliding safety shield to safeguard the needle and operator. The needle depth may be adjusted by sliding the base rod through a Teflon insert; the position may be secured at 10 mm intervals.The experimental apparatus, shown in Figure 3, was used to measure the insertion force and tissue deflection while inserting a needle into a hybrid tissue model. The hybrid tissue model was formed by wrapping bovine liver in porcine skin to simulate needle insertion into human skin. The box containing the tissue model was placed on an air table, allowing the tissue box to float and move more freely. During the force tests a dynamic force sensor (Omega) measured the needle insertion force. The pneumatic insertion device was manually stabilized and the needle tip aligned with a needle grid.Two sets of experiments were performed. In the first set of experiments, the force of an 18-gauge needle inserted into the tissue model was measured using slow manual hand insertion, at approximately 20 mm/s, and high speed insertion with the pneumatic insertion device. The device was powered by pressures of 345 kPa and 690 kPa and generated insertion speeds of approximately 700 mm/s and 1400 mm/s, respectively. In the second experiment the force sensor was removed; the distance the tissue box slid backwards during the 142 mm needle insertion was then measured for both hand insertion and high speed pneumatic insertion using 690 kPa to power the pneumatic insertion device. For both experiments 10 tria