Impact of anatomical changes on simulated proton arc therapy and intensity‐modulated proton therapy for lung cancer

Abstract Purpose : During lung cancer radiotherapy, inter‐fractional anatomical changes may cause the delivered dose to deviate from the primary plan, affecting tumor control and increasing the risk of normal tissue damage. This study aims to evaluate the impact of anatomical changes on the dosimetric and radiobiological performance of simulated proton arc therapy (sPAT) versus intensity‐modulated proton therapy (IMPT) for lung cancer patients under patient‐specific anatomical changes. Methods : Data from 21 lung cancer patients were retrospectively analyzed. The prescribed dose for all patients was 6000 cGy (relative biological effectiveness, RBE). Each patient with a primary planning computed tomography (pCT) and a mid‐treatment adaptive‐planning CT (aCT) acquired at a median of 29 days into treatment due to notable tumor volume changes. Primary plans for sPAT and IMPT were designed on the pCT. After rigid registration of the pCT and aCT, non‐adaptive plans (sPAT p‐a , IMPT p‐a ) were generated by directly recalculating the doses of the primary plans on the aCT. The comparison evaluated the dosimetric impact of anatomical changes by comparing non‐adaptive plans (sPAT p‐a vs. IMPT p‐a ). Dose‐volume histogram (DVH) parameters for targets and organs at risk (OARs) and tumor control probability (TCP) and normal tissue complication probability (NTCP) were evaluated. Results : For the primary plans, sPAT and IMPT achieved similar target coverage, while the doses to OARs were generally lower in sPAT p . Under anatomical changes, both non‐adaptive plans exhibited a decrease in target coverage, sPAT p‐a achieved a D 95% of 5567.57 cGy[RBE] compared with 5423.33 cGy[RBE] for IMPT p‐a ( p < 0.001), indicating that sPAT better preserved target coverage. Compared with the primary plans, sPAT p‐a and IMPT p‐a exhibited TCP reductions of 5.83% and 8.07%, respectively. Conclusions : Compared with IMPT, sPAT exhibits enhanced robustness against inter‐fractional anatomical changes occurring in lung‐cancer radiotherapy.