16th International Symposium on Advanced Science and Technology in Experimental Mechanics

Study for the Effects of Material and Tip Shape on Straight-Line Stability of Needle Tip-Development of Minimally Invasive Needles for Gold Marker Implantation in RadiotherapyUNIVERSITYOFYAMANASHI

Nov. 3-Nov. 6, 2021,Hanoi,Vietnam

Kohei OBATA, Yasumi ITO, Ryuichi YAMADA, Yoshiyuki KAGIYAMA, Masahide SAITO and Hiroshi ONISHI
University of Yamanashi
E-mail：g20tm005@yamanashi.ac.jp, yasumii@yamanashi.ac.jp

Needle straight-line stability evaluation experimentIntroduction

Overview

In the field of radiotherapy, there is moving object tracking
irradiation using Cyberknife. It is a technology that can reduce theirradiation range by irradiating while tracking the gold marker
placed in the body in real time in real time.

Puncture gelatin gel using multiple needles with different tip shapes and flexural rigidity, andinvestigate the effect on straight-line stability .

Use an indwelling needle to indwell the gold marker inside the body

CyberKnife

Material and needle usedGelatin gel was used as the puncture target. The transparent
container made by diluting powder 5 times with hot water at 80 ゜C.
After pouring into (100 mm × 100 mm × 100 mm) andrefrigerating for 48 hours, the one immediately after removal wasused. The needle is assumed to be a 25G needle that is clinicallyused, and has a diameter of 0.5 mm and a length of 170 mm.

Problems when using indwelling needlesThin needle
The deflection of the needle in the bodycauses the position of the gold marker toshift, leading to a decrease in thetherapeutic effectGelatin gel

Tip angle [°]Thick needle
About 10High straight-line stability in thebody, but with risks such as
pneumothorax during puncture

About 20

About 40

About 60

Stainless steel
Pneumothorax incidence for each needle1,2)

The purpose of this study

Tungsten

Aiming to develop a needle with minimal invasiveness and straight-line stability , weinvestigated the effects of needle bending rigidity and tip shape on straight-line stability .

MethodThe images were taken from two directions, the front and the side, and theamount of needle deflection was determined from the images. 90 mm
puncture was performed at a speed of 10 mm / min.

Examination of biomimetic materials for puncture
Overview
Based on the puncture load of porcine muscle and porcine liver, which have similar buffering
performance to humans, we compared the puncture load of dummy skin and gelatin gel to examine
whether it is a biological simulation material suitable for evaluation of puncture behavior.

Materials
The porcine soft tissue was adjusted to 37 ゜C (the temperature close to human body temperature)
in a constant temperature bath.
The gelatin gel used was the one immediately after taking out after diluting the powder 5 times
with hot water at 80 ゜C and refrigerating for 48 hours.
Porcine soft tissue
MuscleFront image

Side image

Biomimetic materials

LiverDummy skinGelatin gel

Results and discussion

Appearance

Thickness [mm]20Method
The clinically used 19G needle (diameter 1.1 mm, length
250 mm) was attached to the upper part of the desktop tester,and each test material was punctured.
Deflection of the needle with a tip angle of 10 degrees

In the gelatin gel, the temperature near the center wasmeasured at the start of puncture and at the end of puncture.
Puncture speed [mm/min]40

Number of punctures

3Results and discussion
Puncture load [N]3Porcine muscle
Porcine liver
Dummy skinGelatin gel

2.521.5
10.5
00

By changing the material of the needle from stainless steel to tungsten, the amount ofdeflection could be reduced at all angles.

10Puncture distance [mm]102030
Displacement [mm]40PorcineMusclePorcineMuscleDummyskinGelatingel

Deflection for each angle at the final position

Compared with a stainless steel needle with a tip angle of 10゜, which is the closest condition toclinically used needles, it was suggested that straight-line stability can be improved bychanging the material and tip angle. In the case of stainless steel with low flexural rigidity, it isconsidered that if the tip angle is small, the contact area with gelatin gel becomes large and alarge amount of deflection occurs. In the case of tungsten, which has high flexural rigidity, theresistance to bending is large, so it is considered that the influence of the tip angle is small andthe amount of deflection is the same.

Inclination
up to 10 mm[N/mm]

Averagepunctureload [N]

0.048

0.65

•

0.0230.29•

0.083

1.70

Conclusions

•
0.037

0.47

Comparing porcine soft tissue and dummy skin, the puncture load was significantly different.
It was confirmed that the rise of the puncture load and the average puncture load of the gelatin
gel were located between the porcine muscle and the liver. (The internal temperature of thegelatin gel at this time was 10 to 13 ゜C.) This suggests that the puncture load on the living
soft tissue can be reproduced by using the gelatin gel in a certain temperature range.

It was clarified that the puncture load of biological soft tissues can be reproduced by using
the gelatin gel at an appropriate temperature.
It was clarified that when a material with low flexural rigidity is used for the needle, the tip
shape affects the straight-line stability, and the straight-line stability can be improved byincreasing the tip angle.
It was clarified that when a material with high flexural rigidity is used for the needle, it has
high straight-line stability regardless of the tip shape.

References
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2) Nikhil Bhagat, Nicholas Fidelman, Jeremy C. Durack, Jeremy Collins, Roy L. Gordon, Jeanne M. LaBerge, Robert K, Kerlan Jr:
Complications Associated with the Percutaneous Insertionof Fiducial Markers in the Thorax, CardioVascular and Interventional
Radiology, Vol.33, No.6, (2010), pp.1186-1191.