Quantifying interobserver variation in target definition in palliative radiotherapy.
OBJECTIVE
To describe the degree of interobserver and intraobserver variability in target and field definition when using three-dimensional (3D) volume- vs. two-dimensional (2D) field-based planning.


METHODS
Standardized case scenario and diagnostic imaging for 9 palliative cases (3 bone metastases, 3 palliative lung cancer, and 3 abdominal pelvis soft-tissue disease) were presented to 5 study radiation oncologists. After a decision on what the intended anatomic target should be, observers created two sets of treatment fields, first using a 2D field-based and then a 3D volume-based planning approach. Percent overlap, under-coverage, and over-coverage were used to describe interobserver and intraobserver variations in target definition.


RESULTS
The degree of interobserver variation for 2D and 3D planning was similar with a degree of overlap of 76% (range, 56%-85%) and 74% (range, 55%-88%), respectively. When comparing the treatment fields defined by the same observer using the two different planning methods, the mean degree of overlap was 78%; over-coverage, 22%; and under-coverage, 41%. There was statistically significantly more under-coverage when field-based planning was used for bone metastases (33%) vs. other anatomic sites (16%) (p = 0.02). In other words, 2D planning is more likely to result in geographic misses in bone metastases compared with other areas.


CONCLUSIONS
In palliative radiotherapy clinically significant interobserver and intraobserver variation existed when using both field- and volume-based planning approaches. Strategies that would reduce this variability deserve further investigation.
Grabarz
Daniel
D
Centro Oncologia Mendel & Associados, Toronto, Ontario, Canada.
Panzarella
Tony
T
Bezjak
Andrea
A
Mclean
Michael
M
Elder
Christine
C
Wong
Rebecca K S
RK
D000008:Abdominal Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy; D001859:Bone Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy* / Q000556:secondary; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D015588:Observer Variation; D010166:Palliative Care / Q000592:standards; D010386:Pelvic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D018787:Radiation Oncology / Q000592:standards; D011859:Radiography; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012983:Soft Tissue Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*