Abstract
BACKGROUND: Radiation therapy is one of the essential treatment modalities for invasive thymomas. Clinically, respiratory motion poses a challenge for the radiotherapy of thoracic tumors. One method to address this issue is to train patients to hold their breath at the end of deep inspiration. The purpose of this retrospective cohort study was to investigate the dosimetric and clinical advantages of the deep inspiration breath-hold (DIBH) technique in postoperative intensity-modulated radiation therapy (IMRT) for thymomas. METHODS: Thymoma patients undergoing postoperative IMRT were included. Each patient underwent two computed tomography (CT) scans, one under free breath (FB) and the other under DIBH. Dosimetric parameters of organs at risk (OARs) were evaluated in three series plans. Dose analysis and volume comparisons were conducted during FB-3 mm (FB with 3 mm internal target volume margin), FB-10 mm (FB with 10 mm internal target volume margin), and DIBH and compared using a paired sample Student's t-test. Normal tissue complication probabilities (NTCP) for lungs and heart were calculated and compared. RESULTS: The total lung volume significantly increased by 31% (4,216±198 vs. 2,884±166 mL) and the heart volume reduced by 12% (552±25 vs. 636±35 mL) between DIBH acquisitions compared to FB. A significant improvement was observed in all the dosimetric parameters (D(mean), V20, V5) of the lung on DIBH compared to FB-3 mm (54%±2.85% vs. 47%±2.90%, P<0.001; 15%±1.37% vs. 12%±1.32%, P=0.004; and 10.28±0.58 vs. 8.76±0.57 Gy, P<0.001, respectively), as well as in the D(max) and D2% of the esophagus and spine. The lung volume increment was related to a reduction in the mean dose of lungs, with a correlation coefficient of r=0.27, P=0.03. The NTCP values for pneumonitis significantly reduced with DIBH compared to the FB state (0.6% vs. 1.1%, P<0.001). CONCLUSIONS: The radiation dose to the OARs can be significantly reduced by using the DIBH technique in postoperative IMRT for thymomas. The increased volume of lungs using DIBH acquisitions can significantly reduce the incidence of pneumonitis.