Single isocenter versus dual isocenter treatment using flattening filter-free and jaw-tracking volumetrically modulated arc therapy for boot-shaped lung cancer: Evaluation of dosimetric and feasibility

Background: To determine whether a dual-isocenter volumetrically modulated arc therapy (VMAT) technique results in lower normal pulmonary dosage compared to a traditional single isocenter technique for boot-shaped lung cancer. Methods: A cohort of 15 patients with advanced peripheral or central lung cancer who had metastases in the mediastinum and supraclavicular lymph nodes was randomly selected for this retrospective study. VMAT plans were generated for each patient using two different beam alignment techniques with the 6-MV flattening filter-free (FFF) photon beam: single-isocenter jaw-tracking VMAT based on the Varian TrueBeam linear accelerator (S-TV), and dual-isocenter VMAT based on both TrueBeam (D-TV) and Halcyon linear accelerator (D-HV). For all 45 treatment plans, planning target volume (PTV) dose coverage, conformity/homogeneity index (CI/HI), mean heart dose (MHD), mean lung dose (MLD) and the total lung tissue receiving 5, 20, 30 Gy (V-5, V-20, V-30) were evaluated. The monitor units (MUs), delivery time, and plan quality assurance (QA) results were recorded. Results: The quality of the objectives of the three plans was comparable to each other. In comparison with S-TV, D-TV and D-HV improved the CI and HI of the PTV (p < 0.05). The MLD was 13.84 +/- 1.44 Gy (mean +/- SD) for D-TV, 14.22 +/- 1.30 Gy and 14.16 +/- 1.42 Gy for S-TV and D-HV, respectively. Lungs-V-5Gy was 50.78 +/- 6.24%, 52.00 +/- 7.32% and 53.36 +/- 8.48%, Lungs-V-20Gy was 23.72 +/- 2.27%, 26.18 +/- 2.86% and 24.96 +/- 3.09%, Lungs-V30Gy was 15.69 +/- 1.76%, 17.20 +/- 1.72% and 16.52 +/- 2.07%. Compared to S-TV, D-TV provided statistically significant better protection for the total lung, with the exception of the lungs-V-5. All plans passed QA according the gamma criteria of 3%/3 mm. Conclusions: Taking into account the dosimetric results and published clinical data on radiation-induced pulmonary injury, dual-isocenter jaw-tracking VMAT may be the optimal choice for treating boot-shaped lung cancer.