4DCT ventilation function image-based functional lung protection for esophageal cancer radiotherapy

Background 4DCT (four-dimensional computed tomography) can effectively obtain functional lung ventilation images for patients and integrate them into radiotherapy treatment planning. Studies have not been performed on esophageal cancer, and there is no clear consensus on the optimal functional lung threshold for functional lung. Methods Functional lung images were generated for 11 patients with esophageal cancer. The correlation between the dose-volume parameters of functional lung (FL) as defined by different thresholds and the change of PFT/PDFT (pulmonary [diffusion] function test) metrics before and after radiotherapy were evaluated. FL-sparing planning was generated for each patient to preserve the functional lung and compared to conventional anatomical CT (non-sparing) planning. Results There was a significant positive correlation between the FL0.8 (defined Jacobian value <= 0.8), FL0.84, and FL0.9 dose-volume parameters and Delta FEV1/FVC (reduction before and after radiotherapy), and the FL0.8-V-30 correlation was the strongest (r = 0.819, P < 0.01). The FL-sparing planning had a target area conformity index and homogeneity index comparable to the non-sparing planning (P > 0.05). For FL, the FL-sparing planning achieved lower FL-MLD (6.30 +/- 2.14 Gy vs. 7.83 +/- 2.70 Gy), V-10 (17.13 +/- 7.70% vs. 27.40 +/- 9.48%), and V-20 (6.96 +/- 3.85% vs. 11.63 +/- 7.19%) compared to the non-sparing planning (P < 0.05), while heart and spinal cord doses were not significantly different between the two planning groups. Conclusion The 4DCT-based FL irradiation dose for esophageal cancer was significantly associated with a decrease in FEV1/FVC. The optimal FL defined as a Jacobian value <= 0.8 or about 21% of the whole lung volume may be a good choice. FL-sparing planning significantly reduced the FL dose without compromising target area coverage.