Geometric Evaluation of Patient-Specific 3D Bolus from 3D Printed Mold and Casting Method for Radiation Therapy

Hyun Joon An; Myeong Soo Kim; Jiseong Kim; Jaeman Son; Chang Heon Choi; Jong Min Park; Jung-in Kim

doi:10.14316/pmp.2019.30.1.32

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An, Kim, Kim, Son, Choi, Park, and Kim: Geometric Evaluation of Patient-Specific 3D Bolus from 3D Printed Mold and Casting Method for Radiation Therapy

Original Article

Progress in Medical Physics 2019;30(1):32-38.

Published online: 19 March 2019

DOI: https://doi.org/10.14316/pmp.2019.30.1.32

Geometric Evaluation of Patient-Specific 3D Bolus from 3D Printed Mold and Casting Method for Radiation Therapy

Hyun Joon An^1,², Myeong Soo Kim^1,², Jiseong Kim^1,², Jaeman Son^1,², Chang Heon Choi^1,^2,³, Jong Min Park^1,^2,^3,⁴, Jung-in Kim^1,^2,^3,

¹Department of Radiation Oncology, Seoul National University Hospital

²Biomedical Research Institute, Seoul National University Hospital

³Institute of Radiation Medicine, Seoul National University Medical Research Center, Seoul

⁴Robotics Research Laboratory for Extreme Environments, Advanced Institutes of Convergence Technology, Suwon, Korea

Corresponding author Jung-in Kim (madangin@gmail.com) Tel: 82-2-2072-3573 Fax: 82-2-3410-2619

Received 29 January 2019 Revised 15 March 2019 Accepted 19 March 2019

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Purpose:

The objective of this study is to evaluate the geometrical accuracy of a patient-specific bolus based on a three-dimensional (3D) printed mold and casting method.

Materials and Methods:

Three breast cancer patients undergoing treatment for a superficial region were scanned using computed tomography (CT) and a designed bolus structure through a treatment planning system (TPS). For the fabrication of patient-specific bolus, we cast harmless certified silicone into 3D printed molds. The produced bolus was also imaged using CT under the same conditions as the patient CT to acquire its geometrical shape. We compared the shapes of the produced bolus with the planned bolus structure from the TPS by measuring the average distance between two structures after a surface registration.

Results and Conclusions:

The result of the average difference in distance was within 1 mm and, as the worst case, the absolute difference did not exceed ±2 mm. The result of the geometric difference in the cross-section profile of each bolus was approximately 1 mm, which is a similar property of the average difference in distance. This discrepancy was negligible in affecting the dose reduction. The proposed fabrication of patient-specific bolus is useful for radiation therapy in the treatment of superficial regions, particularly those with an irregular shape.

Keywords: Bolus, Patient specific bolus, 3D printing, Dose build up, Geometric analysis

REFERENCES

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Fig. 1

(a) Transaxial view of patient CT and designed bolus and (b) volume rendering of designed bolus.

Fig. 2

Overall fabrication process of bolus.

Fig. 3

(a) 3D printed bolus molds with body and lid part, and (b) produced patient-specific bolus.

Fig. 4

(a) Planned bolus structure from TPS, (b) measured fabricated bolus structure, (c) superimposed structures after registration, and (d) color map of difference in distance between two structures.

Fig. 5

Difference in distance of registered structure surface.

Fig. 6

Equal spacing interval cross-section profile map.

Table 1.

Physical property of Dragon Skin^TM 10 MEDIUM and 3D printer settings.

Physical properties of Dragon Skin^TM 10 MEDIUM		Zotrax M300 3D printer setting
Physical Density	1.179 g/cc	Extruder Temperature	245°C
Electron Density ratio compared to water	1.134	Extrusion Width	0.4 mm
Tensile strength	475 psi	Layer Height	0.14 mm
Tensile Modulus	22 psi	Speed	100 mm/s
Elongation at Break	1000 %	Fill Density	0%
Shore Hardness#	10 A	Fill Type	Mesh
		Fill Angle	30°
		Nozzle Diameter	0.4 mm
		Filament Diameter	1.75 mm
		Layer Thickness	0.14 mm
		Print Quality	High

Table 2.

3D modeling information for each structure.

	Patient 1		Patient 2		Patient 3
	Planned	Fabricated	Planned	Fabricated	Planned	Fabricated
Vertices	62682	30866	29460	40088	163398	194514
Facets	125376	61728	58914	80218	326792	389009

Table 3.

Geometric difference of cross-section profile for each patient.

Geometric difference of cross-section profile (mm)
#	Patient 1		Patient 2		Patient 3
#	Mean	STD	Mean	STD	Mean	STD
CS 1	0.82	1.279	0.436	2.209	−0.325	2.237
CS 2	1.076	1.195	0.376	1.166	−0.237	2.044
CS 3	0.721	1.202	0.261	1.572	0.661	1.718
CS 4	0.954	1.645	0.280	1.405	0.369	1.694
CS 5	1.047	1.504	0.743	1.073	−0.055	2.107

STD, standard deviation; CS, cross-section.

Table 4.

Comparison of volume and surface between planned and fabricated bolus.

	Patient 1			Patient 2			Patient 3
	Planned	Fabricated	% diff	Planned	Fabricated	% diff	Planned	Fabricated	% diff
Volume (mm³)	1026.75	938.73	9.0	125.58	114.27	9.4	2084.63	1971.92	5.6
Area (mm²)	2048.63	1938.14	5.5	313.65	304.79	2.9	3000.77	2988.07	0.4

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