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VALUE OF 4D CT SIMULATION IN RADIATION PLANNING FOR STAGE III NON-SMALL CELL LUNG CANCER
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Abstract
Objectives: To evaluate changes in target volumes and dose of organs at risk between 3D and 4D plans. Subjects and methods: A cross-sectional descriptive prospective and retrospective study on 31 non-small cell lung cancer (NSCLC) patients receiving radiotherapy at Military Hospital 175 from July 2020 to July 2022. Gross tumor volume was contoured on 3D CT images (GTV 3D) and on all 10 respiratory phases of 4D CT scans (ITV or GTV 4D) in 31 patients with stage III NSCLC. Both 3D and 4D treatment plans were performed for each patient using planning target volume PTV 3D (derived from a single CTV plus conventional margins) and PTV 4D (derived from 4D internal target volume, which included all 10 CTVs plus setup margins). Target volumes and dose volume histograms were compared for the lung, heart, esophagus, and spinal cord between 3D and 4D treatment plans. Results: The average GTV of the 4D (111.4 ± 69.4 cm³) was larger than the 3D plans (77.7 ± 54.2 cm³) (p = 0.001). However, the average PTV 4D (401.8 ± 167.3 cm³) was less than the PTV 3D (460.2 ± 179.1 cm³) (p = 0.002). The 4D plans spared more surrounding normal tissues than the 3D plans, especially in the lung. Compared with 3D plans, lung mean dose and V5, V10, V20 of the total lung decreased from 18.3Gy, 59.9%, 55.8%, 40.5% to 16.9Gy, 44.6%, 31.2%, 28.9% respectively. The mean dose of heart, esophagus, and the max dose of the spinal cord on the 4D plans were reduced compared with the 3D plans (13.1 Gy, 18.7 Gy, and 37.9 Gy compared with 15,8 Gy, 19,1 Gy, and 40 Gy). However, the difference was not statistically significant (p > 0,05). Conclusion: 4DCT-based plans can reduce the target volumes and spare more normal tissues compared with 3D plans in radiotherapy for NSCLC.
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Keywords
4DCT, Internal target volume, Non-small cell lung cancer, Normal tissue
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