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Review
. 2021 Sep 22;7(4):414.
doi: 10.18063/ijb.v7i4.414. eCollection 2021.

3D Printing Polymer-based Bolus Used for Radiotherapy

Ying Lu  1   2 , Jianbo Song  2 , Xiaohong Yao  1 , Meiwen An  3 , Qinying Shi  2 , Xiaobo Huang  1
Affiliations
Review

3D Printing Polymer-based Bolus Used for Radiotherapy

Ying Lu et al. Int J Bioprint. .

Abstract

Bolus is a kind of auxiliary device used in radiotherapy for the treatment of superficial lesions such as skin cancer. It is commonly used to increase skin dose and overcome the skin-sparing effect. Despite the availability of various commercial boluses, there is currently no bolus that can form full contact with irregular surface of patients' skin, and incomplete contact would result in air gaps. The resulting air gaps can reduce the surface radiation dose, leading to a discrepancy between the delivered dose and planned dose. To avoid this limitation, the customized bolus processed by three-dimensional (3D) printing holds tremendous potential for making radiotherapy more efficient than ever before. This review mainly summarized the recent development of polymers used for processing bolus, 3D printing technologies suitable for polymers, and customization of 3D printing bolus. An ideal material for customizing bolus should not only have the feature of 3D printability for customization, but also possess radiotherapy adjuvant performance as well as other multiple compound properties, including tissue equivalence, biocompatibility, antibacterial activity, and antiphlogosis.

Keywords: 3D printing; Bolus; Hydrogel; Radiotherapy; Soft polymers.

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Conflict of interest statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Figures

Figure 1
Figure 1
Illustration of bolus for the treatment of superficial tumors by radiotherapy. The tumor (red) is located in the subcutaneous tissues. Bolus (blue) is used to increase skin dose and overcome the skin-sparing effect.
Figure 2
Figure 2
Different boluses and their cross-sectional computed tomography (CT) images. Acrylonitrile butadiene styrene (ABS) bolus (A) and its CT image (B) for head radiotherapy (Reproduced from Ref[8] licensed under Creative Commons Attribution 4.0 license). Agilus-60 bolus (C) and its CT image (D) for head radiotherapy (Reproduced from Ref[9] licensed under Creative Commons Attribution 4.0 license). Silicon bolus (E) and its CT image (F) for ear radiotherapy (Reproduced from Ref[10] licensed under Creative Commons Attribution 4.0 license). Hydrogel bolus (G) and its CT image (H) for nose radiotherapy (Reproduced from Ref[10] licensed under Creative Commons Attribution 4.0 license). PCL bolus (I) and its CT image (J) for nose radiotherapy (Reproduced from Ref[12] licensed under Creative Commons Attribution 4.0 license).
Figure 3
Figure 3
Young’s modulus of selected soft polymers (blue) and human tissues (red).
Figure 4
Figure 4
Schematic illustrations of different 3D printing technologies. (A) Fused deposition modeling printing. (B) Direct ink writing printing. (C) Inkjet printing. (D) Stereolithography printing. (E) Digital projection lithography printing. (F) Two-photon polymerization printing.
Figure 5
Figure 5
Some 3D-printed boluses reported in the literature. (A) A nose bolus printed with Tangoplus (Reproduced from Ref[76] licensed under Creative Commons Attribution 4.0 license). (B) A bolus printed with ABS on the head phantom surface (Reproduced from Ref[77] licensed under Creative Commons Attribution 4.0 license). (C) 3D-printed bolus of the 4th and 5th knuckle (Reproduced from Ref[8] licensed under Creative Commons Attribution 4.0 license). (D) 3D-printed bolus fitting the ear of a volunteer (Reproduced from Ref[8] licensed under Creative Commons Attribution 4.0 license). (E) 3D-printed Ninjaflex bolus covering the right-hand side of the head phantom (Reproduced from Ref[78] licensed under Creative Commons Attribution 4.0 license). (F) 3D-printed breast bolus (Reproduced from Ref[79] licensed under Creative Commons Attribution 4.0 license). (G) Bolus printed with PLA on the Alderson RANDO phantom (Reproduced from Ref[80] licensed under Creative Commons Attribution 4.0 license).
Figure 6
Figure 6
(A) Indirect printing workflow of bolus. (B) Direct printing workflow of bolus.
Figure 7
Figure 7
An ideal soft polymer suitable for customized bolus should have combined features, including printability, tissue equivalence, biocompatibility, flexibility, and antibacterial properties.
See this image and copyright information in PMC

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