ABSTRACT
An accurate assessment of the extent of the tumor is critical for successful local treatment of lung cancer by surgery and/or radiotherapy. Guidelines to establish the extent of treatment margins may be derived from correlation studies between pre-treatment imaging and histopathology. Deformations occur, however, between in-vivo CT imaging and ex-vivo pathology due to the softness of lung tissue and pathology processing. The first aim of this study was to quantify these deformations in tissue around non-small cell lung cancer. The second aim was to explore factors associated with the magnitude of the deformations. The study was performed in 25 patients who underwent lobectomy after preoperative CT. Non-rigid registration was employed to evaluate tissue deformations around the gross tumor volume (GTV), taking into account potential differences in elasticity between tumor and healthy lung tissue. Tissue was found to be compacted by approximately 60% depending on circularity of the tumor and orientation of the specimen on the pathology table during processing. The deformations give rise to potential underestimation of the treatment margins in pathology studies that do not take this aspect into account.
Subject(s)
Algorithms , Carcinoma, Non-Small-Cell Lung/diagnostic imaging , Carcinoma, Non-Small-Cell Lung/surgery , Lung Neoplasms/diagnostic imaging , Lung Neoplasms/surgery , Radiographic Image Interpretation, Computer-Assisted/methods , Tomography, X-Ray Computed/methods , Adult , Aged , Female , Humans , Lung , Male , Middle Aged , Postoperative Period , Radiographic Image Enhancement/methods , Reproducibility of Results , Sensitivity and SpecificityABSTRACT
Lower lobe lung tumours in particular can move up to 2 cm in the cranio-caudal direction during the respiration cycle. This breathing motion causes image artefacts in conventional free-breathing computed tomography (CT) and positron emission tomography (PET) scanning, rendering delineation of structures for radiotherapy inaccurate. The purpose of this study was to develop a method for four-dimensional (4D) respiration-correlated (RC) acquisition of both CT and PET scans and to develop a framework to fuse these modalities. The breathing signal was acquired using a thermometer in the breathing airflow of the patient. Using this breathing signal, the acquired CT and PET data were grouped to the corresponding respiratory phases, thereby obtaining 4D CT and PET scans. Tumour motion curves were assessed in both image modalities. From these tumour motion curves, the deviation with respect to the mean tumour position was calculated for each phase. The absolute position of the centre of the tumour, relative to the bony anatomy, in the RCCT and gated PET scans was determined. This 4D acquisition and 4D fusion methodology was performed for five patients with lower lobe tumours. The peak-to-peak amplitude range in this sample group was 1-2 cm. The 3D tumour motion curve differed less than 1 mm between PET and CT for all phases. The mean difference in amplitude was less than 1 mm. The position of the centre of the tumour (relative to the bony anatomy) in the RCCT and gated PET scan was similar (difference <1 mm) when no atelectasis was present. Based on these results, we conclude that the method described in this study allows for accurate quantification of tumour motion in CT and PET scans and yields accurate respiration-correlated 4D anatomical and functional information on the tumour region.
