Evaluation of the hybrid-dynamic conformal arc therapy technique for radiotherapy of lung cancer.

Purpose: A hybrid-dynamic conformal arc therapy (HDCAT) technique consisting of a single half-rotated dynamic conformal arcbeam and static field-in-field beams in two directions was designed and evaluated in terms of dosimetric benefits for radiotherapyof lung cancer. Materials and Methods: This planning study was performed in 20 lung cancer cases treated with the VERO system (BrainLABAG, Feldkirchen, Germany). Dosimetric parameters of HDCAT plans were compared with those of three-dimensional conformalradiotherapy (3D-CRT) plans in terms of target volume coverage, dose conformity, and sparing of organs at risk. Results: HDCAT showed better dose conformity compared with 3D-CRT (conformity index: 0.74 +/- 0.06 vs. 0.62 +/- 0.06, p < 0.001).HDCAT significantly reduced the lung volume receiving more than 20 Gy (V-20: 21.4% +/- 8.2% vs. 24.5% +/- 8.8%, p < 0.001; V-30: 14.2%+/- 6.1% vs. 15.1% +/- 6.4%, p = 0.02; V-40: 8.8% +/- 3.9% vs. 10.3% +/- 4.5%, p < 0.001; and V-50: 5.7% +/- 2.7% vs. 7.1% +/- 3.2%, p < 0.001),V-40 and V-50 of the heart (V40: 5.2 +/- 3.9 Gy vs. 7.6 +/- 5.5 Gy, p < 0.001; V50: 1.8 +/- 1.6 Gy vs. 3.1 +/- 2.8 Gy, p = 0.001), and the maximumspinal cord dose (34.8 +/- 9.4 Gy vs. 42.5 +/- 7.8 Gy, p < 0.001) compared with 3D-CRT. Conclusions: HDCAT could achieve highly conformal target coverage and reduce the doses to critical organs such as the lung,heart, and spinal cord compared to 3D-CRT for the treatment of lung cancer patients.