Comparison of multi-institutional pre-treatment verification for VMAT of nasopharynx with delivery errors

E M Pogson; S Arumugam; C R Hansen; M Currie; S J Blake; N Roberts; M Carolan; P Vial; T Alharthi; L Holloway; D I Thwaites

doi:10.1016/j.ejmp.2018.07.007

Comparison of multi-institutional pre-treatment verification for VMAT of nasopharynx with delivery errors

Phys Med. 2018 Sep:53:25-31. doi: 10.1016/j.ejmp.2018.07.007. Epub 2018 Aug 10.

Authors

E M Pogson¹, S Arumugam², C R Hansen³, M Currie⁴, S J Blake⁵, N Roberts⁶, M Carolan⁷, P Vial⁸, T Alharthi⁹, L Holloway¹⁰, D I Thwaites¹¹

Affiliations

¹ Institute of Medical Physics, School of Physics, Faculty of Science, The University of Sydney, Sydney, New South Wales, Australia; Liverpool and Macarthur Cancer Therapy Centres, Liverpool, NSW, Australia; Ingham Institute for Applied Medical Research, Sydney, NSW, Australia. Electronic address: [email protected].
² Liverpool and Macarthur Cancer Therapy Centres, Liverpool, NSW, Australia.
³ Laboratory of Radiation Physics, Odense University Hospital, Odense, Denmark; Institute of Clinical Research, University of Southern Denmark, Odense, Denmark.
⁴ Illawarra Cancer Care Centre, Wollongong, NSW, Australia.
⁵ Institute of Medical Physics, School of Physics, Faculty of Science, The University of Sydney, Sydney, New South Wales, Australia; Ingham Institute for Applied Medical Research, Sydney, NSW, Australia.
⁶ Ingham Institute for Applied Medical Research, Sydney, NSW, Australia; Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, Australia.
⁷ Illawarra Cancer Care Centre, Wollongong, NSW, Australia; Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, Australia.
⁸ Institute of Medical Physics, School of Physics, Faculty of Science, The University of Sydney, Sydney, New South Wales, Australia; Liverpool and Macarthur Cancer Therapy Centres, Liverpool, NSW, Australia; Ingham Institute for Applied Medical Research, Sydney, NSW, Australia; South Western Sydney Clinical School, University of New South Wales, Sydney, NSW, Australia.
⁹ Institute of Medical Physics, School of Physics, Faculty of Science, The University of Sydney, Sydney, New South Wales, Australia; Liverpool and Macarthur Cancer Therapy Centres, Liverpool, NSW, Australia; Ingham Institute for Applied Medical Research, Sydney, NSW, Australia.
¹⁰ Institute of Medical Physics, School of Physics, Faculty of Science, The University of Sydney, Sydney, New South Wales, Australia; Liverpool and Macarthur Cancer Therapy Centres, Liverpool, NSW, Australia; Ingham Institute for Applied Medical Research, Sydney, NSW, Australia; Laboratory of Radiation Physics, Odense University Hospital, Odense, Denmark; Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, Australia; South Western Sydney Clinical School, University of New South Wales, Sydney, NSW, Australia.
¹¹ Institute of Medical Physics, School of Physics, Faculty of Science, The University of Sydney, Sydney, New South Wales, Australia.

PMID: 30241751
DOI: 10.1016/j.ejmp.2018.07.007

Abstract

Purpose: Measurement-based pre-treatment verification with phantoms frequently uses gamma analysis to assess acceptable delivery accuracy. This study evaluates the sensitivity of a commercial system to simulated machine errors for three different institutions' Volumetric Modulated Arc Therapy (VMAT) planning approaches.

Methods: VMAT plans were generated for ten patients at three institutions using each institution's own protocol (manually-planned at institution 1; auto-planned at institutions 2 and 3). Errors in Multi-Leaf Collimator (MLC) field size (FS), MLC shift (S), and collimator angle (C) of -5, -2, -1, 1, 2 and 5 mm or degrees were introduced. Dose metric constraints discriminated which error magnitudes were considered unacceptable. The smallest magnitude error treatment plans deemed clinically unacceptable (typically for a 5% dose change) were delivered to the ArcCHECK for all institutions, and with a high-dose point ion chamber measurement in 2 institutions. Error detection for different gamma analysis criteria was compared.

Results: Not all deliberately introduced VMAT plan errors were detected using a typical 3D 3%/3 mm global gamma pass rate of 95%. Considering all institutions, gamma analysis was least sensitive to negative FS errors. The most sensitive was a 2%/2 mm global analysis for institution 1, whilst for institution 2 it was 3%/3 mm global analysis. The majority of errors (58/59 for institution 1, 54/60 for institution 3) were detected using ArcCHECK and ion chamber measurements combined.

Conclusions: Not all clinically unacceptable errors are detected. Combining ion chamber measurements with gamma analysis improved sensitivity and is recommended. Optimum gamma settings varied across institutions.

Keywords: 3%/3 mm; Collimator; Errors; Gamma; Global; MLC position; Simulated.

Publication types

Comparative Study

MeSH terms

Humans
Medical Errors*
Nasopharynx / radiation effects*
Quality Assurance, Health Care / methods*
Radiometry
Radiotherapy, Intensity-Modulated*