Biological Image-guided Radiotherapy in Rectal Cancer: Challenges and Pitfalls
(2009) International Journal of Radiation: Oncology - Biology - Physics — Vol. 75, n° 3, p. 782-790 (2009)
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- Purpose: To investigate the feasibility of integrating multiple imaging modalities for image-guided radiotherapy in rectal cancer. Patients and Methods: Magnetic resonance imaging (MRI) and fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT) were performed before, during, and after preoperative chemoradiotherapy (CRT) in patients with resectable rectal cancer. The FDG-PET signals were segmented with an adaptive threshold-based and a gradient-based method. Magnetic resonance tumor volumes (TVs) were manually delineated. A nonrigid registration algorithm was applied to register the images, and mismatch analyses were carried out between MR and FDG-PET TVs and between TVs over time. Tumor volumes delineated on the images after CRT were compared with the pathologic TV. Results: Forty-five FDG-PET/CT and 45 MR images were analyzed from 15 patients. The mean MRI and FDG-PET TVs showed a tendency to shrink during and after CRT. In general, MRI showed larger TVs than FDG-PET. There was an approximately 50% mismatch between the FDG-PET TV and the MRI TV at baseline and during CRT. Sixty-one percent of the FDG-PET TV and 76% of the MRI TV obtained after 10 fractions of CRT remained inside the corresponding baseline TV. On MRI, residual tumor was still suspected in all 6 patients with a pathologic complete response, whereas FDG-PET showed a metabolic complete response in 3 of them. The FDG-PET TVs delineated with the gradient-based method matched closest with pathologic findings. Conclusions: Integration of MRI and FDG-PET into radiotherapy seems feasible. Gradient-based segmentation is recommended for FDG-PET. Spatial variance between MRI and FDG-PET TVs should be taken into account for target definition. (C) 2009 Elsevier Inc.
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Roels, S., Slagmolen, P., Nuyts, J., Lee, J., Loeckx, D., Maes, F., Vandecaveye, V., Stroobants, S., Ectors, N., Penninckx, F., & Haustermans, K. (2009). Biological Image-guided Radiotherapy in Rectal Cancer: Challenges and Pitfalls. International Journal of Radiation: Oncology - Biology - Physics, 75(3), 782-790. https://doi.org/10.1016/j.ijrobp.2008.11.031 (Original work published 2009)