Decreased 3D observer variation with matched CT-MRI, for target delineation in Nasopharynx cancer.
OBJECTIVE
To determine the variation in target delineation of nasopharyngeal carcinoma and the impact of measures to minimize this variation.


METHODS
For ten nasopharyngeal cancer patients, ten observers each delineated the Clinical Target Volume (CTV) and the CTV elective. After 3D analysis of the delineated volumes, a second delineation was performed. This implied improved delineation instructions, a combined delineation on CT and co-registered MRI, forced use of sagittal reconstructions, and an on-line anatomical atlas.


RESULTS
Both for the CTV and the CTV elective delineations, the 3D SD decreased from Phase 1 to Phase 2, from 4.4 to 3.3 mm for the CTV and from 5.9 to 4.9 mm for the elective. There was an increase agreement, where the observers intended to delineate the same structure, from 36 to 64 surface % (p = 0.003) for the CTV and from 17 to 59% (p = 0.004) for the elective. The largest variations were at the caudal border of the delineations but these were smaller when an observer utilized the sagittal window. Hence, the use of sagittal side windows was enforced in the second phase and resulted in a decreased standard deviation for this area from 7.7 to 3.3 mm (p = 0.001) for the CTV and 7.9 to 5.6 mm (p = 0.03) for the CTV elective.


CONCLUSIONS
Attempts to decrease the variation need to be tailored to the specific causes of the variation. Use of delineation instructions multimodality imaging, the use of sagittal windows and an on-line atlas result in a higher agreement on the intended target.
Department of Radiation Oncology, The Netherlands Cancer Institute/Antoni van Leeuwenhoekhuis, Amsterdam, The Netherlands. c.rasch@nki.nl
Coen R N
CR
Rasch
Roel J H M
RJ
Steenbakkers
Isabelle
I
Fitton
Joop C
JC
Duppen
Peter J C M
PJ
Nowak
Frank A
FA
Pameijer
Avraham
A
Eisbruch
Johannes H A M
JH
Kaanders
Frank
F
Paulsen
Marcel
M
van Herk
D006801:Humans; D007090:Image Interpretation, Computer-Assisted; D021621:Imaging, Three-Dimensional; D008279:Magnetic Resonance Imaging; D009303:Nasopharyngeal Neoplasms / Q000453:epidemiology / Q000473:pathology* / Q000532:radiotherapy*; D015588:Observer Variation; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D020266:Radiotherapy, Conformal; D014057:Tomography, X-Ray Computed