Hybrid VMAT for Patients with Large-size Stage III Non-small Cell Lung Cancer

Purpose:To avoid the rapid growth of lung cancer, radiotherapy should be started as soon as possible after diagnosis. Three-dimensional conformal radiotherapy (3D-CRT) is commonly used in Japan; however, lung cancer with vertebral invasion or lymph node metastasis to the bilateral mediastinum cannot be completely cured using 3D-CRT considering the dose constraints for the spinal cord. Therefore, we developed hybrid volumetric modulated arc therapy (hVMAT), a combination of 3D-CRT and VMAT, for patients with large-size stage III non-small cell lung cancer (NSCLC). Here, we assessed its utility.Methods:Eleven patients with large-size stage III NSCLC who underwent hVMAT between May 2010 and August 2013 were enrolled in this study. For all patients, to maintain the spinal cord with dose constraint (maximum dose of <50 Gy in 25 fractions) used for 3D-CRT was impossible. The median total dose and fractionations were 74 Gy and 37 fractions, respectively. A dose of up to 36-40 Gy was used for 3D-CRT, and a dose of up to 30-38 Gy was used for VMAT. The dose constraint for the lung, defined as the percentage of the total lung volume irradiated with 5 Gy and 20 Gy, was less than 50% and 30%, respectively. Nine patients received concurrent chemotherapy, and two received only radiotherapy. We evaluated the following:1)Adverse effects in patients who underwent hVMAT2)Simulated comparison of 3D-CRT and VMAT with hVMAT for PTV D95, lung V5, V20, and mean lung dose (MLD)Results:Only one patient had grade III radiation pneumonitis (RP) during the median 7-month follow-up period, whereas grade I and II RP were observed in 4 and 6 patients, respectively. The mean total values for lung V5, V20, and MLD in patients with grade II or III RP were significantly higher compared with those in patients with grade I RP (48.9% vs. 28.0%, p = 0.027 for V5; 27.0% vs. 14.4%, p = 0.035 for V20; 16.4 Gy vs. 9.0 Gy , p = 0.024 for MLD). No other non-hematological toxicities of more than grade III were observed.PTV D95 for hVMAT was equal to that for VMAT (89.7% vs. 90.8%, p = 0.736) and superior to that for 3D-CRT (89.7% vs. 69.5%, p < 0.001).The total lung dose for hVMAT and VMAT was also equivalent (41.3% vs. 40.2%, p = 0.104 for V5; 22.4% vs. 22.3%, p = 0.856 for V20; 13.7 Gy vs. 14.1 Gy, p = 0.284 for MLD). 3D-CRT exhibited lower V5, but no difference for V20 and MLD in comparison with hVMAT (31.7% vs. 41.3%, p < 0.001 for V5; 21.9% vs. 22.4%, p = 0.386 for V20; 13.2 Gy vs. 13.7 Gy, p = 0.152 for MLD).Conclusion:In addition to VMAT, hVMAT could be another treatment option for large-size stage III NSCLC.

SSA22-06

Hybrid VMAT for Patients with Large-size Stage III Non-small Cell Lung Cancer