ESTRO 2025 - Abstract Book

S3666

Physics - Quality assurance and auditing

ESTRO 2025

3413

Poster Discussion A pilot multicentre audit of the geometric accuracy and water equivalence of 3D printed thermoplastic test objects for use in radiotherapy Matthew R Jones 1 , Conor K McGarry 2,3 , Catharine H Clark 4,5 , Peter D Woolliams 6 , Matthew A Bolt 1 , Owen McLaughlin 7 , Maria Boutros 8 , Tristan Wright 9 , Rhys Jenkins 10 , Anna Tonino 11 , Fiona Milliken 12 , Neil Bentley 13 , Gordon D Sands 14 , James C L Burnley 15 , Paul J Doolan 16 , Dualta McQuaid 1 , Geoff J Budgell 17 , Elizabeth J Adams 18 1 Radiotherapy Physics, The Royal Surrey NHS Foundation Trust, Guildford, United Kingdom. 2 Radiotherapy Physics, Belfast Health and Social Care Trust, Belfast, United Kingdom. 3 Patrick G Johnston Centre for Cancer Research, Queen’s University Belfast, Belfast, United Kingdom. 4 Radiotherapy Physics, University College London Hospital, London, United Kingdom. 5 Medical Physics and Biomedical Engineering, University College London, London, United Kingdom. 6 Materials and Mechanical Metrology, National Physical Laboratory, London, United Kingdom. 7 Patrick G. Johnston Centre for Cancer Research, Queen's University Belfast, Belfast, United Kingdom. 8 Radiotherapy Physics, University College London Hospitals NHS Foundation Trust, London, United Kingdom. 9 Oncology Physics, Edinburgh Cancer Centre, Edinburgh, United Kingdom. 10 Medical Physics & Clinical Engineering, Singleton Hospital, Swansea, United Kingdom. 11 Radiotherapy Physics, Imperial College Healthcare NHS Trust, London, United Kingdom. 12 Radiotherapy, Ninewells Hospital, Dundee, United Kingdom. 13 Regional Radiation Protection Service, The Royal Surrey NHS Foundation Trust, Guildford, United Kingdom. 14 Research, Leo Cancer Care, Crawley, United Kingdom. 15 Radiotherapy Physics, Mount Vernon Cancer Centre, Northwood, United Kingdom. 16 Medical Physics, German Oncology Center, Limassol, Cyprus. 17 Christie Medical Physics and Engineering, The Christie NHS Foundation Trust, Manchester, United Kingdom. 18 Medical Physics, The Royal Surrey NHS Foundation Trust, Guildford, United Kingdom Purpose/Objective: The developing use of 3D printing in radiotherapy means that fabrication of custom phantoms is increasingly feasible. The use of plastic materials as water substitutes is well established, and local printing of dosimetric phantoms for use in QA, research and multicentre audits can be both beneficial and inexpensive. However, the dosimetric properties of thermoplastic polymers used in 3D printing, such as PLA, can vary significantly. This study presents a pilot multicentre audit to quantify variations in geometric accuracy, radiodensity and water-mimicking properties of test objects printed at different centres. Ten participating centres printed sets of three standard PLA blocks, using provided stereolithography (STL) files, with infills of 80, 90 and 100%. One block also featured protruding and recessed circular details, on horizontal and vertical faces, with a range of diameters. Block dimensions and details printed thereon were measured to determine achievable geometric accuracy. HU data were measured from CT scans of the blocks, taken both locally and at the coordinating centre, and the infills corresponding to water equivalence estimated from fitted trendlines. Attenuation measurements were taken through varying configurations of the blocks using a custom printed phantom and ionisation chamber, for 6MV photon beams from a Varian TrueBeam. This data was used to calculate Material/Methods: