Patterns of Local-Regional Failure After Intensity Modulated Radiation Therapy or Passive Scattering Proton Therapy With Concurrent Chemotherapy for Non-Small Cell Lung Cancer

Purpose: We compared differences in patterns of locoregional failure, and the influence of adaptive planning on those patterns, in patients who received passive scattering proton therapy (PSPT) versus intensity modulated photon therapy (IMRT) for non-small cell lung cancer. Methods and Materials: Treatment simulation computed tomography scans and dose distributions were registered with images depicting the recurrence. Local failure (LF) was defined as failure within the internal target volume (ITV); marginal failure (MF) as failure between the ITV and planning target volume (PTV) plus a 10-mm margin (PTV_+10mm); and regional failure (RF) as outside the PTV_+10mm. Weekly during-treatment 4-dimensional computed tomography simulation and verification plans were obtained for all patients. Adaptive plans were developed if the verification plan showed deviations in protocol-specified dose distribution, and failure locations were recorded for those patients as well. Results: Of the 212 patients analyzed, most (152 [72%]) had no failure; of the 60 patients with failure, 27 (45%) had LF (within the ITV), 23 (38%) had MF (between the ITV and PTV_+10mm), and 10 (17%) had RF (>10 mm outside the PTV). MF rates were no different for IMRT patients (16 of 136 [12%]) or PSPT patients (7 of 76 [9%], log-rank P =.558). The only independent predictor of MF on Cox proportional hazards analysis was T3-4 status. Large tumors and use of PSPT independently predicted the need for adaptive planning. Although 5-year overall survival rates were poorer for patients with large tumors versus small tumors (P <.001), the rates were similar for patients with large tumors who received adaptive planning versus small tumors. Conclusions: No differences in LF, MF, or RF patterns were found for IMRT versus PSPT. Proton therapy more often required adaptive planning, and the techniques used for adaptive planning did not compromise tumor control. Response to chemoradiation by larger tumors predicted favorable survival.