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3D-printed Bolus in Radiotherapy
good transparency (≥50%) will help to facilitate the
accurate and repeatable placement of bolus. Good
mechanical performance means that the bolus not only
has an elastic modulus similar to the skin tissues, but
also good toughness to prevent it from being torn in
repeated use. The bioadhesive performance enables the
3D printed bolus to fit well with the irregular human
skin, ensuring the accuracy of radiation dose. (iii) The
favorable compatibility means that an ideal 3D-printed
bolus should not generate any adverse effects in contact
with human body. Besides, antibacterial properties can
inhibit the occurrence of inflammation caused by the
side effect of radiotherapy. Therefore, to obtain an ideal
3D printed bolus, the convergence of versatility in the
soft polymers is inevitable in the future, and is thought
to accelerate the outcome of radiotherapy.

Figure 7. An ideal soft polymer suitable for customized bolus should Acknowledgments
have combined features, including printability, tissue equivalence,
biocompatibility, flexibility, and antibacterial properties. This work was supported by the National
Natural Science Foundation of China (31300808),
biocompatibility, good-fit to skin contour as well as the Natural Science Foundation of Shanxi Province
antibacterial and antiphlogosis properties (Figure 7). (201801D121094), the Open Research Fund Program of
In brief, there has been impressive progress in Collaborative Innovation Center for Molecular Imaging
the application of 3D printing technology in many of Precision Medicine, No. 2020-ZD02.
areas. However, as an emerging technology used in
radiotherapy, 3D printing still faces numerous challenges Conflicts of Interest
before practical applications, including printing methods, The authors declare that they have no known competing
printable materials, and boluses’ design. Through financial interests or personal relationships that could
reviewing the 3D printing techniques and polymers have appeared to influence the work reported in this paper.
suitable for processing bolus, we anticipate this review
could help readers choose suitable printing methods Author contributions
and design printable polymer materials to achieve the
customization of bolus. Y.L. collected information and drafted the manuscript.
An ideal 3D-printed bolus for radiotherapy is J.S. advised the organization of the main contents. X.Y.
an auxiliary device that should integrate multiple and M.A. reviewed the manuscript. Q.S. collected the
properties, including customizable dimensions, detailed research results. X.H. conceived the ideas and
appropriate physicochemical performance, and edited the manuscript.
favorable compatibility and antibacterial activity. (i) The References
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38 International Journal of Bioprinting (2021)–Volume 7, Issue 4