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Defining and assessing an anisotropic delineation margin for modern radiotherapy
L R Bell1, E M Pogson2, P E Metcalfe1
1Centre for Medical Radiation Physics, University of Wollongong, Wollongong 2522, Australia and Liverpool and Macarthur Cancer Therapy Centres, Ingham Institute, Liverpool 2170, Australia.
Medical Physics
|December 3, 2016
Summary
Anisotropic margins improve radiotherapy accuracy by accounting for inter-observer variation in target volume delineation. This method is superior for large target volumes, reducing both missed malignant and included healthy tissue.
Area of Science:
- Radiotherapy Physics
- Medical Imaging
- Radiation Oncology
Background:
- Uncertainty in target volume delineation significantly impacts radiotherapy dosimetry and patient outcomes.
- Delineation uncertainty is often overlooked as a source of error in clinical practice.
- Historically, other sources of uncertainty have received more attention than delineation variability.
Purpose of the Study:
- To define and assess an anisotropic delineation margin to account for spatially varying delineation uncertainty.
- To utilize a whole breast radiotherapy cohort as a proof of concept for the anisotropic margin.
- To compare anisotropic and conventional delineation margin approaches.
Main Methods:
- Utilized 21 whole breast radiotherapy patient datasets with clinical target volumes delineated by eight observers.
- Determined anisotropic delineation margins in polar and spherical coordinates based on inter-observer standard deviation.
- Compared anisotropic margins to conventional cardinal direction margins by assessing target volume coverage and tissue inclusion/exclusion.
Main Results:
- Anisotropic margins achieved >95% clinical target volume (CTV) coverage in 79-92% of cases.
- Less than 1% malignant tissue was missed in 65-91% of cases, and less than 37% healthy tissue was included in 89-97% of cases.
- Anisotropic margins were superior for large target volumes (>1400 cm³), offering better CTV coverage and reduced healthy tissue inclusion.
Conclusions:
- All tested margin methods adequately encompassed inter-observer variation.
- The anisotropic approach demonstrated superiority over conventional methods for large target volumes (>1400 cm³).
- This validated methodology for whole breast radiotherapy can be applied to other anatomical sites.
