Room: AAPM ePoster Library
Purpose: To assess respiratory-induced stomach motion and deformation as well as interfractional deformation, and if/how these should be incorporated in radiation treatment planning.
Methods: Five gastric cancer patients with 4-6 fiducial markers distributed over the stomach for pre-operative image-guided radiotherapy were included. On all available 4DCTs (3-4 per patient, 17 in total), the markers (25 in total) were manually delineated; their center of mass (COM) per scan was determined for every end-inhale and end-exhale scan. COM respiratory amplitude was determined in superoinferior (SI), anteroposterior (AP), and left-right (LR) directions. For each scan, the marker-COM distances were measured, from which the maximum observed difference in distance (maximum rigid body error; RBEmax) was determined, between end-inhale and end-exhale (intrafractional deformation) and between the first end-inhale scan and their respective repeat scans (interfractional deformation). Difference in respiratory motion between markers at most proximal and distal part of the stomach was evaluated.
Results: COM respiratory amplitude was larger in SI than AP direction (average[range], 8.0[3.9-13.3] mm vs. 3.2[1.4-5.4] mm, paired t-test: p<0.001), and larger in AP than LR direction (1.4[0.1-3.7], p<0.001). Interfractional deformation was larger than intrafractional deformation (RBEmax median[range], 9.7[7.1-18.2] mm vs. 2.3[0.5-5.9] mm, Wilcoxon signed-rank: p<0.001). Overall, 3D COM respiratory amplitude (median[range], 9.0[4.5-13.5] mm) was larger than intrafractional deformation (p<0.001). With respect to the proximal stomach, the distal stomach moves superior (average 1.8 mm, paired t-test: p=0.007), posterior (2.2 mm, p=0.02) and left (1.8 mm, p=0.005) upon inhalation.
Conclusion: Respiratory-induced stomach motion is substantial and differs between the proximal and distal part of the stomach. Respiratory-induced motion/deformation should be incorporated in treatment margins or dealt with by tracking/gating. Conversely, magnitude and character of the interfractional deformations imply these should be managed by adaptive radiotherapy. However, more data is needed for (anisotropic) margin calculations and determination of a suitable adaptive radiotherapy strategy.
Funding Support, Disclosures, and Conflict of Interest: This work was funded by the Dutch Cancer Society (KWF Kankerbestrijding; Grant No. KWF 10882).