Reduction of observer variation using matched CT-PET for lung cancer delineation: a three-dimensional analysis.

Marcel Van Herk, Roel J H M Steenbakkers, Joop C Duppen, Isabelle Fitton, Kirsten E I Deurloo, Lambert J Zijp, Emile F I Comans, Apollonia L J Uitterhoeve, Patrick T R Rodrigus, Gijsbert W P Kramer, Johan Bussink, Katrien De Jaeger, José S A Belderbos, Peter J C M Nowak, Marcel van Herk, Coen R N Rasch

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    PURPOSE: Target delineation using only CT information introduces large geometric uncertainties in radiotherapy for lung cancer. Therefore, a reduction of the delineation variability is needed. The impact of including a matched CT scan with 2-[18F]fluoro-2-deoxy-D-glucose positron emission tomography (FDG-PET) and adaptation of the delineation protocol and software on target delineation in lung cancer was evaluated in an extensive multi-institutional setting and compared with the delineations using CT only. METHODS AND MATERIALS: The study was separated into two phases. For the first phase, 11 radiation oncologists (observers) delineated the gross tumor volume (GTV), including the pathologic lymph nodes of 22 lung cancer patients (Stages I-IIIB) on CT only. For the second phase (1 year later), the same radiation oncologists delineated the GTV of the same 22 patients on a matched CT-FDG-PET scan using an adapted delineation protocol and software (according to the results of the first phase). All delineated volumes were analyzed in detail. The observer variation was computed in three dimensions by measuring the distance between the median GTV surface and each individual GTV. The variation in distance of all radiation oncologists was expressed as a standard deviation. The observer variation was evaluated for anatomic regions (lung, mediastinum, chest wall, atelectasis, and lymph nodes) and interpretation regions (agreement and disagreement; i.e., >80% vs. 0. For all anatomic regions, the interpretation differences among the radiation oncologists were reduced. The amount of disagreement was 45% and 18% for the first and second phase, respectively. Furthermore, the mean delineation time (12 vs. 16 min, p
    Original languageEnglish
    JournalInternational journal of radiation oncology, biology, physics
    Issue number2
    Publication statusPublished - 1 Feb 2006


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