ESTRO 2025 - Abstract Book

S3171

Physics - Inter-fraction motion management and offline adaptive radiotherapy

ESTRO 2025

Additionally, the benefits of a replanning were also investigated for both photon and proton therapy of lung cancer patients.

Material/Methods: The study included 83 stage III/IV (non)-small cell lung cancer patients treated with concurrent (n=53) or sequential (n=30) chemoradiation with an available repeat CT of the treatment. For all patients a treatment plan on the planning CT, a dose recalculation on the repeat CT, and a replanning on the repeat CT were performed for both photon and proton therapy. These dose distributions were compared in terms of dose and NTCP. The dose evaluation criteria included criteria for target coverage (V95%≥95%) and maximum organ-at-risk dose. The NTCP evaluation criteria included a ≥10 percent point (pp) difference in NTCP for grade≥2 dysphagia and grade≥2 pneumonitis, and a ≥2 pp difference in NTCP for two-year mortality. Results: Out of 83 patients, 28 showed no or minimal anatomical changes, 23 had tumor regression, 29 atelectasis or pleural effusion and 3 patients had other changes. Figure 1 shows the results of the dose recalculation on the repeat CT for each anatomical subgroup. The percentage of patients passing the dose evaluation criteria for photons/protons were 89%/64% in case of no or minimal anatomical changes, 83%/52% for tumor regression, and 24%/14% for atelectasis or pleural effusion. Figure 2 shows the results of the dose recalculation and replanning on the repeat CT. In patients who passed the dose evaluation criteria, the NTCP criteria failed in 6% of the photon plans and 11% of the proton plans, and the number of patients that benefitted substantially from replanning was 13% for photons and 17% for protons, with the most evident NTCP improvements in patients with tumor regression.