Target delineation in post-operative radiotherapy of brain gliomas: interobserver variability and impact of image registration of MR(pre-operative) images on treatment planning CT scans.
OBJECTIVE
To investigate the interobserver variability of intracranial tumour delineation on computed tomography (CT) scans using pre-operative MR hardcopies (CT+MR(conv)) or CT-MR (pre-operative) registered images (CT+MR(matched)).


METHODS
Five physicians outlined the 'initial' clinical tumour volume (CTV0) of seven patients affected by HGG and candidates for radiotherapy (RT) after radical resection. The observers performed on screen-tumour delineation using post-operative CT images of the patients in the treatment position and pre-operative MR radiographs (CT+MR(conv)); they also outlined CTV0 with both CT and corresponding MR axial image on screen (CT+MR(matched)). The accuracy of the image fusion was quantitatively assessed. An analysis was conducted to assess the variability among the five observers in CT+MR(conv) and CT+MR(matched) modality.


RESULTS
The registration accuracy in 3D space is always less than 3.7 mm. The concordance index was significantly better in CT+MR(matched) (47.4+/-12.4%) than in CT+MR(conv) (14.1+/-12.7%) modality (P<0.02). The intersecting volumes represent 67+/-15 and 24+/-18% of the patient mean volume for CT+MR(matched) and CT+MR(conv), respectively (P<0.02).


CONCLUSIONS
The use of CT and MR registered imaging reduces interobserver variability in target volume delineation for post-operative irradiation of HGG; smaller margins around target volume could be adopted in defining irradiation technique.
Cattaneo
Giovanni Mauro
GM
Medical Physics, Scientific Institute, H.S. Raffaele, Milano, Italy. cattaneo.mauro@hsr.it
Reni
Michele
M
Rizzo
Giovanna
G
Castellone
Pietro
P
Ceresoli
Giovanni Luca
GL
Cozzarini
Cesare
C
Ferreri
Andrés José Maria
AJ
Passoni
Paolo
P
Calandrino
Riccardo
R
D000328:Adult; D000368:Aged; D001932:Brain Neoplasms / Q000473:pathology / Q000532:radiotherapy* / Q000601:surgery*; D003131:Combined Modality Therapy; D019583:Dose Fractionation, Radiation; D005260:Female; D005910:Glioma / Q000473:pathology / Q000532:radiotherapy* / Q000601:surgery*; D006801:Humans; D021621:Imaging, Three-Dimensional; D008279:Magnetic Resonance Imaging / Q000592:standards*; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D015203:Reproducibility of Results; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed / Q000592:standards*