Room: Exhibit Hall | Forum 5
Purpose: To assess the accuracy of deformable image registrations between 4DCT average intensity images (AVG) from different weeks for dose accumulation in lung adaptive radiotherapy.
Methods: Fifty non-small cell lung cancer patients previously treated were imported into a commercial treatment planning system. Hybrid Intensity-based deformable image registrations (DIR) were performed between planning 4DCT and 4DCT obtained after 4 weeks of treatment based on the corresponding AVGs, end-inhale phases (T0), mid-ventilation phases (T3), and end-exhale phases (T5). Sixteen bifurcation landmarks uniformly distributed in the superior-inferior direction of the ipsilateral lung were identified on all three phases and copied onto the corresponding AVG image in the same 4DCT. Target registration error (TRE) of each landmark was obtained for DIR of each image pair.
Results: DIR evaluation has been performed on a subset of the patients to date. For the selected 3 patient cases, their mean TREs of landmarks in T0s, T3s, and T5s with AVG-AVG DIR were 5.4 mm, 5.0 mm, and 4.3 mm, respectively, as compared to 4.6 mm, 4.0 mm, and 3.7 mm with T0-T0, T3-T3, and T5-T5 DIRs. TRE increased as the landmarks were located in more inferior portion of the lung due to their larger breathing motions. The landmark that experienced 30.5 mm displacement in a full breathing cycle resulted in the largest mean TRE for AVG-AVG DIR (8.2 mm) and phase-phase DIRs (7.9 mm).
Conclusion: Based on our analysis, the accuracy of DIR between average-intensity images is sufficient for dose accumulation when tumor movement is small. When tumor experiences larger breathing motions, DIR between end-exhale phases is recommended.
Funding Support, Disclosures, and Conflict of Interest: This research is funded by RaySearch Laboratories.