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

J Appl Clin Med Phys. 2019 Jan;20(1):348-355. doi: 10.1002/acm2.12489. Epub 2018 Nov 7.


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 V95% (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, V95% ) 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.

Keywords: 3D printing; hydrogel; radiotherapy; silica gel; tissue compensator.

MeSH terms

  • Computer Simulation
  • Ear Neoplasms / radiotherapy
  • Head / radiation effects
  • Humans
  • Hydrogels / chemistry*
  • Nose Neoplasms / radiotherapy
  • Organs at Risk / radiation effects
  • Parotid Neoplasms / radiotherapy
  • Phantoms, Imaging*
  • Photons / therapeutic use*
  • Printing, Three-Dimensional / instrumentation*
  • Radiotherapy Dosage
  • Radiotherapy Planning, Computer-Assisted / methods*
  • Silica Gel / chemistry*


  • Hydrogels
  • Silica Gel