A dosimetric study on the use of 3D-printed customized boluses in photon therapy: A hydrogel and silica gel study.

Purpose: The aim of the study was to compare the dose differences between two kinds of materials (silica gel and hydrogel) used to prepare boluses based on three-dimensional (3D) printing technologies and commercial bolus in head phantoms simulating nose, ear, and parotid gland radiotherapy.
Methods and Materials: We used 3D printing technology to make silica gel and hydrogel boluses. To evaluate the clinical feasibility, intensity modulated radiation therapy (IMRT) plans were created for head phantoms that were bolus-free or had a commercial bolus, a silica gel bolus, or a hydrogel bolus. Dosimetry differences were compared in simulating nose, ear, and parotid gland radiotherapy separately.
Results: The air gaps were smaller in the silica gel and hydrogel bolus than the commercial one. In nose plans, it was shown that the V _95% (relative volume that is covered by at least 95% of the prescription dose) of the silica gel (99.86%) and hydrogel (99.95%) bolus were better than the commercial one (98.39%) and bolus-free (87.52%). Similarly, the homogeneity index (HI) and conformity index (CI) of the silica gel (0.06; 0.79) and hydrogel (0.058; 0.80) bolus were better than the commercial one (0.094; 0.72) and bolus-free (0.59; 0.53). The parameters of results (HI, CI, V _95% ) were also better in 3D printing boluses than in the commercial bolus or without bolus in ear and parotid plans.
Conclusions: Silica gel and hydrogel boluses were not only good for fit and a high level of comfort and repeatability, but also had better parameters in IMRT plans. They could replace the commercial bolus for clinical use.
(© 2018 The Authors. Journal of Applied Clinical Medical Physics published by Wiley Periodicals, Inc. on behalf of American Association of Physicists in Medicine.)