Modeling daily changes in organ-at-risk anatomy in a cohort of pancreatic cancer patients
Purpose: To characterize daily geometrical variations of gastrointestinal organs with respect to pancreatic tumors, through a population-based statistical model. Materials and methods: The study included 131 CT scans from 35 pancreatic cancer patients treated with Stereotactic Body Radiotherapy (SBRT). For each patient, day-to-day anatomical variations of the stomach, the duodenum and the bowel were assessed from the deformation vector fields (DVF) obtained by non-rigidly registering the contours of the fractions to the planning CT scans. For the whole population, day-to-day motion-deformation patterns were abstracted using principal component analysis (PCA) on the set of DVFs mapped on a reference patient. Based on these geometrical variations, anatomies were generated to create population-based dose-volume histograms (DVH) per patient, which were also compared to clinical values. Results: Through PCA, the most dominant directions of daily deformations were localized in the abdominal organs. Common patterns were found, such as stomach contraction–expansion in the anterior–posterior direction ranging from 5 to 13 mm, and superior-inferior deformations on the bowel from 7 to 14 mm. The duodenum resulted to move laterally, but in a lesser extent (4–8 mm). The populationbased DVHs derived from the model mostly included the daily DVHs observed in the clinic (in >90% of the cases). Conclusions: Anatomical variations influence the delivered doses to healthy organs during SBRT. A motion model was successfully built and explored to extract the larger directions of movement of the gastrointestinal organs. Day-to-day motion modeling can potentially be used to account for geometrical uncertainties in future plan optimization and in online adaptive strategies.
|Keywords||Organ motion management, Daily geometric variations, Statistical motion-deformation model, PCA, SBRT, Pancreas|
|Persistent URL||dx.doi.org/10.1016/j.radonc.2019.01.030, hdl.handle.net/1765/116169|
|Journal||Radiotherapy & Oncology|
Magallon-Baro, A., Loi, M., Milder, M.T.W., Granton, P.V., Zolnay, A.G., Nuyttens, J.J., & Hoogeman, M.S. (2019). Modeling daily changes in organ-at-risk anatomy in a cohort of pancreatic cancer patients. Radiotherapy & Oncology, 134, 127–134. doi:10.1016/j.radonc.2019.01.030