COMPARISON OF HYBRID TECHNIQUES WITH 3D-CONFORMAL RADIOTHERAPY IN PATIENTS WITH LUNG CANCER.

Purpose: It's postulated that hybrid techniques (HT) with lower weighting of IMRT/VMAT component would improve lung dose-volume parameters despite some disadvantage in PTV homogeneity index (HI) and target coverage (TC). Material and Methods: Conformal plans were prepared using 6-10-15 MV-X photon energies while IMRT/VMAT plans of HTs were prepared using 6MV-X. Four HTs were developed having two different ratios (10% and 50%) of IMRT/VMAT component (h-IMRT1, h-IMRT2 and h-VMAT1, h-VMAT2, respectively). HTs were compared with 3D-CRT in terms of HI and TC for PTV, and total lung (TL) and contralateral lung (CL) V5Gy, V10Gy, V20Gy and mean lung dose (MLD). Results: All HTs were advantageous for HI and TC, while disadvantageous for TL and CL-V5Gy. H-IMRT2 provided better TC than h-IMRT1, and so did h-VMAT2 compared to h-VMAT1. Lower weighting of IMRT/VMAT decreased TL and CL-V5Gy in HTs. In addition, h-IMRT1 decreased TL and CL-MLD and CLV20Gy compared to h-IMRT2, while h-VMAT2 decreased TL-V20Gy and CL-MLD compared to h-VMAT2. Conclusion: In the RT of lung tumors close to vertebra, it may be appropriate to suggest a ratio of IMRT/VMAT component approximately 10% in order to decrease the low and intermediate dose-wash lung volume, if HI and TC values are acceptable. [ABSTRACT FROM AUTHOR]