Room: Exhibit Hall | Forum 7
Purpose: To evaluate dosimetric changes in target volumes and organs at risk (OARs) of patients with large-volume non-small cell lung cancer (NSCLC) who underwent intensity-modulated radiation therapy (IMRT) based on deformation registration techniques.
Methods: Thirty patients treated with IMRT for large-volume NSCLC with twice 4DCT scans acquired before radiotherapy (CT1) and after 20 fractions of radiotherapy (CT2) were used for the study. The original plan (Plan1) and second plan (Plan2) were calculated on the average density projection CT of CT1 and CT2 respectively. The dose distribution of Plan1 and Plan2 were accumulated by rigid registration method and deformable registration method to obtain Plan-rig and Plan-def, respectively. The volume of GTV and OARs between CT1 and CT2 were compared, as well as the dosimetric differences among Plan1, Plan2, Plan-rig and Plan-def.
Results: The mean volume of GTV and heart on CT2 decreased by 44.2% and 5.5% from CT1, respectively, while the mean volume of ipsilateral lung, contralateral lung and total lung increased by 5.2%, 6.2% and 5.8%, respectively. The differences were statistically significant (P < 0.05). For the D95, D98 and V100% of IGTV and PTV on Plan2 didnâ€™t change significantly from Plan2 (P > 0.05). The dose-volume parameters of spinal-cord, heart, ipsilateral lung and total lung on Plan2, Plan-rig and Plan-def were significantly lower than those on Plan1 (P < 0.05). Among them, mean heart dose decreased by 15.2%, 6.6%, 7.4%, respectively, and mean lung dose decreased by 15.7%, 6.2%, 6.9%, respectively. The Dice similarity coefficients (DSCs) after deformation registration were significantly higher than those after rigid registration (P < 0.05).
Conclusion: With tumor regression during IMRT, the dose of OARs changed significantly. Therefore, the dose-volume parameters of original plan have great errors in predicting radioactive damage, and those obtained by deformable registration are better.
Funding Support, Disclosures, and Conflict of Interest: Funding Support: Key Research Program of Shandong province (No. 2018GSF118006)