Feasibility of 3D printed air slab diode caps for small field dosimetry

  • Benjamin PerrettEmail author
  • Paul Charles
  • Tim Markwell
  • Tanya Kairn
  • Scott Crowe
Scientific Paper


Commercial diode detectors used for small field dosimetry introduce a field-size-dependent over-response relative to an ideal, water-equivalent dosimeter due to high density components in the body of the detector. An air gap above the detector introduces a field-size-dependent under-response, and can be used to offset the field-size-dependent detector over-response. Other groups have reported experimental validation of caps containing air gaps for use with several types of diodes in small fields. This paper examines two designs for 3D printed diode air caps for the stereotactic field diode (SFD)—a cap containing a sealed air cavity, and a cap with an air cavity at the face of the SFD. Monte Carlo simulations of both designs were performed to determine dimensions for an air cavity to introduce the desired dosimetric correction. Various parameter changes were also simulated to estimate the dosimetric uncertainties introduced by 3D printing. Cap layer dimensions, cap density changes due to 3D printing, and unwanted air gaps were considered. For the sealed design the optimal air gap size for water-equivalent cap material was 0.6 mm, which increased to 1.0 mm when acrylonitrile butadiene styrene in the cap was simulated. The unsealed design had less variation, a 0.4 mm air gap is optimal in both situations. Unwanted air pockets in the bore of the cap and density changes introduced by the 3D printing process can potentially introduce significant dosimetric effects. These effects may be limited by using fine print resolutions and minimising the volume of cap material.


Small field Dosimetry Diode 3D printing Correction free Monte Carlo 



BFB 3D Touch and ABS printing material were provided by the Department of Nuclear Medicine, Royal Brisbane & Womens Hospital, Herston, Australia. Computational resources and services used in the work were provided by the High Performance Computing and Research Support Unit, QUT, Brisbane, Australia.

Compliance with ethical standards

Conflicts of interest

All authors declare they have no conflicts of interest.

Ethical approval

This article does not contain any studies with human participants or animals performed by the authors.


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Copyright information

© Australasian College of Physical Scientists and Engineers in Medicine 2017

Authors and Affiliations

  • Benjamin Perrett
    • 1
    • 2
    Email author
  • Paul Charles
    • 1
    • 2
  • Tim Markwell
    • 3
  • Tanya Kairn
    • 1
    • 4
  • Scott Crowe
    • 1
    • 5
  1. 1.Science and Engineering FacultyQueensland University of TechnologyBrisbaneAustralia
  2. 2.Department of Radiation OncologyPrincess Alexandra HospitalWoolloongabbaAustralia
  3. 3.Mater Cancer Care CentreSouth BrisbaneAustralia
  4. 4.Genesis Cancer Care QueenslandThe Wesley Medical CentreAuchenflowerAustralia
  5. 5.Cancer Care ServicesRoyal Brisbane and Womens HospitalHerstonAustralia

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