Physical considerations on discrepancies in target volume delineation.
OBJECTIVE
To compare the delineations and interpretations of target volumes by physicians in different radio-oncology centers.


METHODS
Eleven Swiss radio-oncology centers delineated volumes according to ICRU 50 recommendations for one prostate and one head and neck case. In order to evaluate the consistency of the volume delineations, the following parameters were determined: 1) the target volumes (GTV, CTV and manually expanded PTV) and their extensions in the three main axes and 2) the correlation of the volume delineated by each pair of centers using the ratio of the intersection to the union (called proximity index).


RESULTS
The delineated prostate volume was 105+/-55 cm(3) for the CTV and 218+/-44 cm(3) for the PTV. The delineated head and neck volume was 46+/-15 cm(3) for the GTV, 327+/-154 cm(3) for the CTV and 528+/-106 cm(3) for the PTV. The mean proximity index for the prostate case was 0.50+/-0.13 for the CTV and 0.57+/-0.11 for the PTV. The proximity index for the head and neck case was 0.45+/-0.09 for the GTV, 0.42+/-0.13 for the CTV and 0.59+/-0.06 for the PTV.


CONCLUSIONS
Large discrepancies between all the delineated target volumes were observed. There was an inverse relationship between the CTV volume and the margin between CTV and PTV, leading to less discrepancies in the PTV than is the CTV delineations. There was more spread in the sagittal and frontal planes due to CT pixel anisotropy, which suggests that radiation oncologists should delineate the target volumes not only in the transverse plane, but also in the sagittal and frontal planes to improve the delineation by allowing a consistency check.
Moeckli
Raphaël
R
University Institute for Radiation Physics, Grand-Pré 1, 1007 Lausanne, Switzerland. Raphael.Moeckli@chuv.ch
Sozzi
Wendy Jeanneret
WJ
Mirimanoff
René-Olivier
RO
Ozsahin
Mahmut
M
Zouhair
Abderrahim
A
Valley
Jean-François
JF
Bochud
François
F
D006258:Head and Neck Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy*; D006801:Humans; D008297:Male; D009367:Neoplasm Staging; D049268:Positron-Emission Tomography; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods* / Q000592:standards; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods; D012680:Sensitivity and Specificity; D013557:Switzerland; D014057:Tomography, X-Ray Computed / Q000379:methods