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.