Single-Isocenter Online Adaptive Radiotherapy for Multi-Lesion Lung Cases: Dosimetric Gains and Time Efficiency
Abstract
Purpose
Lung cancer cases frequently involve multiple lesions, and treatment with a single isocenter can introduce geometric uncertainties, particularly due to inter-fraction motion. Online adaptive radiotherapy (ART) offers a strategy to mitigate these effects. This study evaluates the dosimetric impact and treatment efficiency of CBCT-guided online ART for multi-lesion lung cases treated using a single-isocenter multi-lesion (SIML) approach, compared with single-isocenter single-lesion (SISL), and assesses the impact of lesion-to-isocenter distance on target coverage in scheduled (non-adapted) plans.
Methods
A retrospective analysis included 25 lung cancer patients with ≥2 lesions, comprising 152 treatment fractions delivered on a CBCT-guided adaptive platform (Varian Ethos). PTV margins ranged from 3–7 mm (typically 5 mm). Of these, 92 fractions used SIML (227 lesion–fraction evaluations) and 60 used SISL (60 lesion–fraction evaluations). Lesion-to-isocenter distances in the SIML group ranged from 0.03 cm to 16.68 cm. PTV V100% was analyzed for scheduled and adapted plans to quantify dosimetric gain from adaptation. In the SIML group, scheduled plan coverage was further evaluated as a function of lesion-to-isocenter distance. Treatment efficiency was estimated as treatment time per lesion, defined as session duration divided by the number of lesions treated per plan.
Results
In scheduled plans, PTV coverage was lower in SIML than SISL (84.7 ± 17.0% vs 91.6 ± 8.7%), while adapted plans achieved comparable coverage (96.0 ± 2.1% vs 95.1 ± 1.3%). In SIML treatments, scheduled plan PTV coverage decreased with lesion-to-isocenter distance. Treatment time per lesion was significantly shorter with SIML (26.6 ± 8.4 min) than SISL (50.5 ± 15.8 min).
Conclusion
CBCT-guided online ART using a SIML approach achieves target coverage comparable to SISL in adapted plans while reducing treatment time per lesion, even across a wide range of lesion-to-isocenter distances. These findings support the feasibility and potential clinical benefit of SIML adaptive workflows.