Utilising pseudo-CT data for dose calculation and plan optimization in adaptive radiotherapy.
To quantify the dose calculation error and resulting optimization uncertainty caused by performing inverse treatment planning on inaccurate electron density data (pseudo-CT) as needed for adaptive radiotherapy and Magnetic Resonance Imaging (MRI) based treatment planning. Planning Computer Tomography (CT) data from 10 cervix cancer patients was used to generate 4 pseudo-CT data sets. Each pseudo-CT was created based on an available method of assigning electron density to an anatomic image. An inversely modulated radiotherapy (IMRT) plan was developed on each planning CT. The dose calculation error caused by each pseudo-CT data set was quantified by comparing the dose calculated each pseudo-CT data set with that calculated on the original planning CT for the same IMRT plan. The optimization uncertainty introduced by the dose calculation error was quantified by re-optimizing the same optimization parameters on each pseudo-CT data set and comparing against the original planning CT. Dose differences were quantified by assessing the Equivalent Uniform Dose (EUD) for targets and relevant organs at risk. Across all pseudo-CT data sets and all organs, the absolute mean dose calculation error was 0.2 Gy, and was within 2 % of the prescription dose in 98.5 % of cases. Then absolute mean optimisation error was 0.3 Gy EUD, indicating that that inverse optimisation is impacted by the dose calculation error. However, the additional uncertainty introduced to plan optimisation is small compared the sources of variation which already exist. Use of inaccurate electron density data for inverse treatment planning results in a dose calculation error, which in turn introduces additional uncertainty into the plan optimization process. In this study, we showed that both of these effects are clinically acceptable for cervix cancer patients using four different pseudo-CT data sets. Dose calculation and inverse optimization on pseudo-CT is feasible for this patient cohort.
Liverpool and Macarthur Cancer Therapy Centers and Ingham Institute for Applied Medical Science, Room 302, Medical Foundation Building, 92-94 Parramatta Road, Camperdown, Sydney, NSW, 2050, Australia. brendan.whelan@sydney.edu.au.|Radiation Physics Laboratory, University of Sydney, Sydney, Australia. brendan.whelan@sydney.edu.au.|Institute of Medical Physics, School of Physics, University of Sydney, Sydney, Australia. brendan.whelan@sydney.edu.au.
Brendan
B
Whelan
Liverpool and Macarthur Cancer Therapy Centers and Ingham Institute for Applied Medical Science, Room 302, Medical Foundation Building, 92-94 Parramatta Road, Camperdown, Sydney, NSW, 2050, Australia.|University of New South Wales, Sydney, Australia.
Shivani
S
Kumar
Australian e-Health Research Centre, CSIRO Computational Informatics, Sydney, Australia.
Jason
J
Dowling
Liverpool and Macarthur Cancer Therapy Centers and Ingham Institute for Applied Medical Science, Room 302, Medical Foundation Building, 92-94 Parramatta Road, Camperdown, Sydney, NSW, 2050, Australia.
Jarrad
J
Begg
University of Newcastle, Newcastle, Australia.
Jonathan
J
Lambert
Liverpool and Macarthur Cancer Therapy Centers and Ingham Institute for Applied Medical Science, Room 302, Medical Foundation Building, 92-94 Parramatta Road, Camperdown, Sydney, NSW, 2050, Australia.|University of New South Wales, Sydney, Australia.|University of Western Sydney, Sydney, Australia.
Karen
K
Lim
Liverpool and Macarthur Cancer Therapy Centers and Ingham Institute for Applied Medical Science, Room 302, Medical Foundation Building, 92-94 Parramatta Road, Camperdown, Sydney, NSW, 2050, Australia.|University of New South Wales, Sydney, Australia.|University of Western Sydney, Sydney, Australia.
Shalini K
SK
Vinod
University of Newcastle, Newcastle, Australia.|Calvary Mater Newcastle, Newcastle, Australia.
Peter B
PB
Greer
Liverpool and Macarthur Cancer Therapy Centers and Ingham Institute for Applied Medical Science, Room 302, Medical Foundation Building, 92-94 Parramatta Road, Camperdown, Sydney, NSW, 2050, Australia.|Institute of Medical Physics, School of Physics, University of Sydney, Sydney, Australia.|Centre for Medical Radiation Physics, University of Wollongong, Wollongong, Australia.|University of New South Wales, Sydney, Australia.
Lois
L
Holloway
D000465:Algorithms; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed / Q000379:methods*; D002583:Uterine Cervical Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy
Adaptive radiotherapy; Electron density; Inverse treatment; MRI treatment planning; Planning