KEY POINTS
- This single-institution retrospective study included 180 patients with lung or thymic malignancies treated with intensity-modulated proton therapy between 2020 and 2023.
- Adaptive replanning was required in 41 patients (22.8%), with 56 total replans. Main triggers included tumor shrinkage (33.9%), clinical target volume changes (17.8%), lung anatomy changes (16.1%), and pleural effusion (12.5%).
- Several initial-plan parameters differed between replanned and non-replanned patients, including clinical target volume, heart volume, plan maximum dose, mean lung dose, lung V20, lung V5, mean heart dose, heart V50, and spinal cord maximum dose.
- In multivariable analysis, only clinical target volume and heart volume remained independent predictors. Per 100 cubic centimetre increase, replanning odds increased by 15% for clinical target volume (odds ratio 1.15, 95% confidence interval 1.02–1.31) and 26% for heart volume (odds ratio 1.26, 95% confidence interval 1.03–1.55).
- Optimal cutoff values were 191 cubic centimetres for clinical target volume and 888 cubic centimetres for heart volume. Replanning probability rose from 9.2% to 39.0% above the target-volume cutoff and from 17.5% to 53.8% above the heart-volume cutoff.
CLINICAL TAKEAWAY
Initial planning parameters may help identify thoracic proton therapy patients who need closer surveillance and more frequent quality assurance computed tomography during treatment. The results are useful for workflow triage, but they come from a retrospective single-centre cohort and should be validated before being used as strict replanning rules.