Fortin, DominiqueBasran, Parminder SBerrang, TanyaPeterson, DavidWai, Elaine S2015-06-032015-06-0320142014-02-10Fortin et al.: Deformable versus rigid registration of PET/CT images for radiation treatment planning of head and neck and lung cancer patients: a retrospective dosimetric comparison. Radiation Oncology 2014 9:50http://www.ro-journal.com/content/9/1/50http:/dx.doi.org/10.1186/1748-717X-9-50http://hdl.handle.net/1828/6226BioMed CentralBackground: The purpose of this study is to evaluate the clinical impact of using deformable registration in tumor volume definition between separately acquired PET/CT and planning CT images. Methods: Ten lung and 10 head and neck cancer patients were retrospectively selected. PET/CT images were registered with planning CT scans using commercially available software. Radiation oncologists defined two sets of gross tumor volumes based on either rigidly or deformably registered PET/CT images, and properties of these volumes were then compared. Results: The average displacement between rigid and deformable gross tumor volumes was 1.8 mm (0.7 mm) with a standard deviation of 1.0 mm (0.6 mm) for the head and neck (lung) cancer subjects. The Dice similarity coefficients ranged from 0.76-0.92 and 0.76-0.97 for the head and neck and lung subjects, respectively, indicating conformity. All gross tumor volumes received at least 95% of the prescribed dose to 99% of their volume. Differences in the mean radiation dose delivered to the gross tumor volumes were at most 2%. Differences in the fraction of the tumor volumes receiving 100% of the radiation dose were at most 5%. Conclusions: The study revealed limitations in the commercial software used to perform deformable registration. Unless significant anatomical differences between PET/CT and planning CT images are present, deformable registration was shown to be of marginal value when delineating gross tumor volumes.enDeformableRegistrationPET/CTTreatmentPlanningArticleAttribution-NonCommercial-NoDerivs 2.5 CanadaDepartment of Physics and Astronomy