A multicentre audit of the geometric accuracy and water equivalence of 3D printed thermoplastic objects for use in radiotherapy

Matthew R. Jones; Peter D Woolliams; Matthew A. Bolt; Owen McLaughlin; Maria Boutros; Tristan Wright; Rhys Jenkins; Anna Tonino; Fiona Milliken; Neil Bentley; Gordon D Sands; James C. L. Burnley; Paul J Doolan; Dualta McQuaid; Geoff J Budgell; Elizabeth J. Adams; Conor K. McGarry; Catharine H. Clark

doi:10.1016/j.phro.2026.101006

A multicentre audit of the geometric accuracy and water equivalence of 3D printed thermoplastic objects for use in radiotherapy

Matthew R. Jones^*
, Peter D Woolliams
, Matthew A. Bolt
, Owen McLaughlin
, Maria Boutros
, Tristan Wright
, Rhys Jenkins
, Anna Tonino
, Fiona Milliken
, Neil Bentley
, Gordon D Sands
, James C. L. Burnley
, Paul J Doolan
, Dualta McQuaid
, Geoff J Budgell
, Elizabeth J. Adams
, Conor K. McGarry
, Catharine H. Clark

^*Corresponding author for this work

Research output: Contribution to journal › Article › peer-review

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Abstract

Background and purpose
Plastic materials are widely used as water substitutes in radiotherapy; however, the dosimetric properties of thermoplastic polymers used in 3D printing can vary. A multicentre audit was conducted to quantify variations in geometric accuracy, density and water-mimicking properties of 3D-printed objects.

Materials and methods
Ten centres printed three polylactic acid (PLA) blocks at varying infills. Block dimensions, including protruding and recessed discs, were measured and the blocks weighed to determine geometric accuracy and mass density. Computed tomography (CT) scans were used to derive the printed infills and mass densities corresponding to water equivalence. Tissue phantom ratios (TPRs) were measured for 6 MV photon beams and compared to vendor-provided reference data for water.

Results
A mean error of (-0.2 ± 0.3) mm (mean ± standard deviation, SD) was found for all printed dimensions and disc diameters. Measured CT numbers and mass densities varied by up to 200 Hounsfield units (HU) and 0.20 g/cm3 between centres, respectively. Printed infill and mass densities producing water-equivalent CT density were calculated as (94.5 ± 3.5)% and (1.10 ± 0.03) g/cm3, respectively. Calculated water-equivalent thicknesses formed using combinations of the blocks varied by up to 3.0 mm between centres, with measured TPR data varying by up to 1.2%. Measured and calculated data were normally distributed across centres and fell within ± 2 SD of their respective means. TPR data closely emulated reference values for water.

Conclusions
A multicentre audit was completed to develop understanding of geometric and dosimetric errors associated with 3D printing in radiotherapy.

Original language	English
Article number	101006
Number of pages	8
Journal	Physics and Imaging in Radiation Oncology
Volume	39
DOIs	https://doi.org/10.1016/j.phro.2026.101006
Publication status	Published - 25 May 2026

Keywords

Density
Radiotherapy
PLA
Audit
Infill
3D-printing

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A multicentre audit of the geometric accuracy and water equivalence of 3D printed thermoplastic objects for use in radiotherapy
Copyright 2026 the authors. This is an open access article published under a Creative Commons Attribution-NonCommercial-NoDerivs License (https://creativecommons.org/licenses/by-nc-nd/4.0/), which permits distribution and reproduction for non-commercial purposes, provided the author and source are cited.
Final published version, 2.39 MBLicence: CC BY-NC-ND

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Jones, M. R., Woolliams, P. D., Bolt, M. A., McLaughlin, O., Boutros, M., Wright, T., Jenkins, R., Tonino, A., Milliken, F., Bentley, N., Sands, G. D., Burnley, J. C. L., Doolan, P. J., McQuaid, D., Budgell, G. J., Adams, E. J., McGarry, C. K., & Clark, C. H. (2026). A multicentre audit of the geometric accuracy and water equivalence of 3D printed thermoplastic objects for use in radiotherapy. Physics and Imaging in Radiation Oncology, 39, Article 101006. https://doi.org/10.1016/j.phro.2026.101006

@article{0d37f7ec8eea4336bb3f443f21431ad3,

title = "A multicentre audit of the geometric accuracy and water equivalence of 3D printed thermoplastic objects for use in radiotherapy",

abstract = "Background and purpose Plastic materials are widely used as water substitutes in radiotherapy; however, the dosimetric properties of thermoplastic polymers used in 3D printing can vary. A multicentre audit was conducted to quantify variations in geometric accuracy, density and water-mimicking properties of 3D-printed objects. Materials and methods Ten centres printed three polylactic acid (PLA) blocks at varying infills. Block dimensions, including protruding and recessed discs, were measured and the blocks weighed to determine geometric accuracy and mass density. Computed tomography (CT) scans were used to derive the printed infills and mass densities corresponding to water equivalence. Tissue phantom ratios (TPRs) were measured for 6 MV photon beams and compared to vendor-provided reference data for water. Results A mean error of (-0.2 ± 0.3) mm (mean ± standard deviation, SD) was found for all printed dimensions and disc diameters. Measured CT numbers and mass densities varied by up to 200 Hounsfield units (HU) and 0.20 g/cm3 between centres, respectively. Printed infill and mass densities producing water-equivalent CT density were calculated as (94.5 ± 3.5)\% and (1.10 ± 0.03) g/cm3, respectively. Calculated water-equivalent thicknesses formed using combinations of the blocks varied by up to 3.0 mm between centres, with measured TPR data varying by up to 1.2\%. Measured and calculated data were normally distributed across centres and fell within ± 2 SD of their respective means. TPR data closely emulated reference values for water. Conclusions A multicentre audit was completed to develop understanding of geometric and dosimetric errors associated with 3D printing in radiotherapy.",

keywords = "Density, Radiotherapy, PLA, Audit, Infill, 3D-printing",

author = "Jones, \{Matthew R.\} and Woolliams, \{Peter D\} and Bolt, \{Matthew A.\} and Owen McLaughlin and Maria Boutros and Tristan Wright and Rhys Jenkins and Anna Tonino and Fiona Milliken and Neil Bentley and Sands, \{Gordon D\} and Burnley, \{James C. L.\} and Doolan, \{Paul J\} and Dualta McQuaid and Budgell, \{Geoff J\} and Adams, \{Elizabeth J.\} and McGarry, \{Conor K.\} and Clark, \{Catharine H.\}",

year = "2026",

month = may,

day = "25",

doi = "10.1016/j.phro.2026.101006",

language = "English",

volume = "39",

journal = "Physics and Imaging in Radiation Oncology",

issn = "2405-6316",

publisher = "Elsevier Ireland Ltd",

}

Jones, MR, Woolliams, PD, Bolt, MA, McLaughlin, O, Boutros, M, Wright, T, Jenkins, R, Tonino, A, Milliken, F, Bentley, N, Sands, GD, Burnley, JCL, Doolan, PJ, McQuaid, D, Budgell, GJ, Adams, EJ, McGarry, CK & Clark, CH 2026, 'A multicentre audit of the geometric accuracy and water equivalence of 3D printed thermoplastic objects for use in radiotherapy', Physics and Imaging in Radiation Oncology, vol. 39, 101006. https://doi.org/10.1016/j.phro.2026.101006

TY - JOUR

T1 - A multicentre audit of the geometric accuracy and water equivalence of 3D printed thermoplastic objects for use in radiotherapy

AU - Jones, Matthew R.

AU - Woolliams, Peter D

AU - Bolt, Matthew A.

AU - McLaughlin, Owen

AU - Boutros, Maria

AU - Wright, Tristan

AU - Jenkins, Rhys

AU - Tonino, Anna

AU - Milliken, Fiona

AU - Bentley, Neil

AU - Sands, Gordon D

AU - Burnley, James C. L.

AU - Doolan, Paul J

AU - McQuaid, Dualta

AU - Budgell, Geoff J

AU - Adams, Elizabeth J.

AU - McGarry, Conor K.

AU - Clark, Catharine H.

PY - 2026/5/25

Y1 - 2026/5/25

N2 - Background and purpose Plastic materials are widely used as water substitutes in radiotherapy; however, the dosimetric properties of thermoplastic polymers used in 3D printing can vary. A multicentre audit was conducted to quantify variations in geometric accuracy, density and water-mimicking properties of 3D-printed objects. Materials and methods Ten centres printed three polylactic acid (PLA) blocks at varying infills. Block dimensions, including protruding and recessed discs, were measured and the blocks weighed to determine geometric accuracy and mass density. Computed tomography (CT) scans were used to derive the printed infills and mass densities corresponding to water equivalence. Tissue phantom ratios (TPRs) were measured for 6 MV photon beams and compared to vendor-provided reference data for water. Results A mean error of (-0.2 ± 0.3) mm (mean ± standard deviation, SD) was found for all printed dimensions and disc diameters. Measured CT numbers and mass densities varied by up to 200 Hounsfield units (HU) and 0.20 g/cm3 between centres, respectively. Printed infill and mass densities producing water-equivalent CT density were calculated as (94.5 ± 3.5)% and (1.10 ± 0.03) g/cm3, respectively. Calculated water-equivalent thicknesses formed using combinations of the blocks varied by up to 3.0 mm between centres, with measured TPR data varying by up to 1.2%. Measured and calculated data were normally distributed across centres and fell within ± 2 SD of their respective means. TPR data closely emulated reference values for water. Conclusions A multicentre audit was completed to develop understanding of geometric and dosimetric errors associated with 3D printing in radiotherapy.

AB - Background and purpose Plastic materials are widely used as water substitutes in radiotherapy; however, the dosimetric properties of thermoplastic polymers used in 3D printing can vary. A multicentre audit was conducted to quantify variations in geometric accuracy, density and water-mimicking properties of 3D-printed objects. Materials and methods Ten centres printed three polylactic acid (PLA) blocks at varying infills. Block dimensions, including protruding and recessed discs, were measured and the blocks weighed to determine geometric accuracy and mass density. Computed tomography (CT) scans were used to derive the printed infills and mass densities corresponding to water equivalence. Tissue phantom ratios (TPRs) were measured for 6 MV photon beams and compared to vendor-provided reference data for water. Results A mean error of (-0.2 ± 0.3) mm (mean ± standard deviation, SD) was found for all printed dimensions and disc diameters. Measured CT numbers and mass densities varied by up to 200 Hounsfield units (HU) and 0.20 g/cm3 between centres, respectively. Printed infill and mass densities producing water-equivalent CT density were calculated as (94.5 ± 3.5)% and (1.10 ± 0.03) g/cm3, respectively. Calculated water-equivalent thicknesses formed using combinations of the blocks varied by up to 3.0 mm between centres, with measured TPR data varying by up to 1.2%. Measured and calculated data were normally distributed across centres and fell within ± 2 SD of their respective means. TPR data closely emulated reference values for water. Conclusions A multicentre audit was completed to develop understanding of geometric and dosimetric errors associated with 3D printing in radiotherapy.

KW - Density

KW - Radiotherapy

KW - PLA

KW - Audit

KW - Infill

KW - 3D-printing

U2 - 10.1016/j.phro.2026.101006

DO - 10.1016/j.phro.2026.101006

M3 - Article

SN - 2405-6316

VL - 39

JO - Physics and Imaging in Radiation Oncology

JF - Physics and Imaging in Radiation Oncology

M1 - 101006

ER -

A multicentre audit of the geometric accuracy and water equivalence of 3D printed thermoplastic objects for use in radiotherapy

Abstract

Keywords

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