Stereotactic Body Radiotherapy for Lung Lesions using Multiple Phase 3D-CT Based on the Analysis of Radiobiological Parameters

Introduction: Planning target volume (PTV) is generated from internal treatment volume (ITV) using four-dimensional computed tomography (4D-CT) for enhanced therapeutic gain in the stereotactic body radiotherapy for lung lesions (SBRT-Lung). This study aimed to propose a strategy to generate ITV on multiple-phase 3D-CT and enhance therapeutic gain in SBRT-Lung. Material and Methods: This study was conducted on 6 peripherally located and 5 centrally located lung lesions suitable for SBRT. The PTV was delineated based on 3D-CT datasets acquired at three different phases of respiratory motion. The prescribed dose of 50 Gy in 5 fractions was delivered using RapidArc technique. The therapeutic-gain was compared based on tumor control probability (TCP) and normal tissue complication probability (NTCP) against a multicenter trial, which uses single-phase 3D-CT for PTV delineation. The TCP and NTCP were calculated by Poisson’s linear-quadratic and Lyman-Kutcher-Burman models, respectively. Results: Regarding the multicentre trial, the PTVs were maximally reduced to 42% and 57% among the 6 peripherally and 5 centrally located lung lesions, respectively. In peripheral lung lesions, TCP was significantly enhanced to 0.6% for long-term (>5years) local control (P<0.05), and NTCP was significantly reduced in pneumonitis (Grade≥II) of lung (0.2%; P<0.05). In central lung lesions, TCP was insignificantly enhanced; however, NTCPs were maximally reduced for cartilage necrosis in trachea (35%) and myelitis in spinal cord (19%). Conclusion: The proposed strategy reduced the complications for normal tissues and enhanced therapeutic gain. The successful clinical outcomes validated our hypothesis in short-term (6-12 months), and we are currently testing the long-term efficacy.