A comparison of coordinate systems for use in determining a radiotherapy delineation margin for whole breast

17th International Conference on the Use of Computers in Radiation Therapy

物理学;计算机科学

Pogson, E.M.^1,2 ; Bell, L.^1,2 ; Batumalai, V.^2,3 ; Koh, E.S.^2,3 ; Delaney, G.^2,3 ; Metcalfe, P.^1,2 ; Holloway, L.^1,4

Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW 2522, Australia^1

Liverpool and Macarthur Cancer Therapy Centres, Ingham Institute, Liverpool, NSW, Australia^2

SWSCS, University of New South Wales, Sydney, Australia^3

Institute of Medical Physics, University of Sydney, Sydney, Australia^4

关键词: Anterior posteriors;    Anterior-posterior position;    Cartesian coordinate;    Centre of mass;    Clinical target volumes;    Co-ordinate system;    Observer variations;    Standard deviation;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/489/1/012057/pdf
DOI  :  10.1088/1742-6596/489/1/012057

学科分类：计算机科学（综合）

来源: IOP

【 摘 要 】

Cartesian co-ordinates, traditionally used for radiotherapy margins, calculated at 6 points, may not adequately represent changes in inter-observer contour variation as necessary to define a delineation margin. As a first step, this study compared the standard deviation (SD) in contour delineation using Polar and Cartesian co-ordinates for whole breast. Whole breast Clinical Target Volumes (CTV) were delineated by eight observers for 9 patients. The SD of contour position was determined for Polar co-ordinates at 1° increments for 5 slices and averaged across all patients. The mean centre of mass (COM) was used as the origin for the right breast, for the left the COM was shifted 1cm superiorly to avoid clipping. The SD was determined for Cartesian co-ordinates for medial-lateral and anterior-posterior positions. At slice Z=0cm considering Polar co-ordinates, the SD peaked medially reaching 3.55cm at 15° for the right breast, and 1.44cm at 171° for the left. The SD of the remaining slices maintained a similar distribution, with variation in the peak occurring within 10° of the Z=0cm positions. By comparison, for Cartesian co-ordinates at slice Z=0cm, the largest SD in the medial-lateral and anterior-posterior directions was 0.54/0.57cm and 1.03/0.67cm respectively for right/left breasts. The SD for inter-observer variation for whole breast varies with anatomical position. The maximum SD determined with Polar co-ordinates was greater than with Cartesian coordinates. A delineation margin may thus need to vary with angle over the entire structure and Cartesian co-ordinates may not be the best approach for margin determination for whole breast.