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International Journal of Bioprinting 3D bioprinting of boluses for radiotherapy

the designed gel exhibited non-toxicity and is suitable Table 1. Summary of the thickness and width of designed and
for applications involving skin contact (Figure 5B). printed rectangular boluses
Furthermore, F-actin staining was used to determine
their biocompatibility (Figure 5C). The MTT assay Sample Length (cm) Width (cm) Thickness (cm)
results depicted in Figure 5D demonstrate that there was Design 5 5 0.5
no significant deviation in cell viability among the gels Rectangle 1 5.1 4.9 0.5
throughout the culture period, thus further validating their Rectangle 2 5 5 0.5
biocompatibility.
3.7. Stability of gel A nose bolus composed of the composite gel was
Hydrogels are generally prone to water loss, which greatly fabricated via DLP printing. Axial CT images demonstrated
affects their stability and performance. To overcome this that the printed bolus can effectively eliminate air gaps,
issue, GLY was employed as a partial substitute for water ensuring adequate dose coverage in the build-up region.
in the gel formulation, which gave rise to an organic In contrast, the use of commercial bolus resulted in air gap
photosensitive gel with anti-dehydration properties . formation (as depicted in Figure 7), with approximately
[40]
The variations in CT number and electron density (ED) 15% of slices exhibiting air gaps larger than 5 mm. The
for different gels over time are illustrated in Figure 6A and printed bolus exhibited a close conformity to the intended
B, respectively. Figure S4 (Supplementary File) displays design, as demonstrated in Figure 7 and the dose volume
the changes of mass density (MD) with time for different histogram (DVH) curves for all plans shown in Figure S6
hydrogels. The initial mean values of composite gel’s HU (Supplementary File). DVH analysis indicated that
and relative RD were 127 ± 2 HU and 1.077 ± 0.001, 3D-printed bolus significantly enhanced D95% (dose
respectively. No significant differences were observed in covering 95% of volume) for PTV, compared with
the initial 15 h for gels containing GLY. The results of RD commercial bolus. Table 2 presents detailed dosimetric
measurements also confirmed the tissue equivalence of the comparisons between the printed bolus and the control
composite gel. Furthermore, the gel demonstrated minimal group. The use of both 3D-printed and commercial boluses
moisture loss and maintained its structural integrity within resulted in improved dose coverage compared to the
a humidity range of 40% to 60% (Figure 6C). Conversely, group without using boluses. The 3D-printed and virtual
the control groups without GLY experienced significant boluses exhibited superior performance in terms of target
shrinkage (an approximate reduction from 1/3 to 1/2) conformity indices (CI) and homogeneity indices (HI) for
within a mere 15 h, underscoring the pivotal role of GLY IMRT and VMAT plans compared to commercial boluses.
in water conservation. This phenomenon can be ascribed
to the intermolecular interactions between GLY and water, In this study, the utilization of soft gel material for direct
where GLY forms hydrogen bonds with water molecules, printing of bolus significantly simplified the production
thereby hindering the evaporation of water. process. The exceptional conformity to clinical model is an
attribute that makes gel bolus a potential tool in addressing
The gels exhibit excellent anti-dehydration properties, current clinical challenges associated with commercial
which make them highly promising materials for boluses in radiotherapy. Moreover, the DVH curves
applications in the field of radiotherapy. It should be noted indicated that the gel possessed near-water equivalent
that increasing the concentration of GLY decreases the rate dosimetric transmission and exhibited dose distributions
of water loss, and the content of GLY has a strong influence in accordance with virtual boluses, thereby eliminating the
on the changes in HU and ED over time. Besides, the need for need for multiple rounds of CT scanning.
special storage conditions is obviated if the gels contain GLY.
4. Conclusion
3.8. Radiological properties
To evaluate the dimensional accuracy of DLP printing, a In summary, this study introduced a DN gel that can be
caliper with a resolution of 0.1 mm was used to measure fabricated into a customized bolus for radiotherapy in
the actual size of a printed gel and determine deviations treating superficial tumors. Specifically, by formulating a
(Table 1). The results indicate that the maximum photocurable ink consisting of acrylamide as the monomer,
measured differences between the designed and printed PEGDA as the crosslinker, LAP as the photoinitiator, and
dimensions of the products were less than 1 mm on PA as an anti-bacterial agent in a glycerol-water system,
average, demonstrating the effectiveness of the printing we printed a gel-based bolus via DLP printing technology.
method in producing structures with high shape fidelity The designed material is compatible with photocurable
requirements. Boluses for head radiotherapy are shown in 3D bioprinting, allowing for personalized customization
Figure S5 (Supplementary File). and eliminating gaps commonly encountered in the

Volume 10 Issue 2 (2024) 259 doi: 10.36922/ijb.1589