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 local-regional failure, and the influence of adaptive planning on those patterns, in patients given passive scattering proton therapy (PSPT) vs. intensity-modulated photon therapy (IMRT) for non-small cell lung cancer.

METHODS: Treatment simulation CT scans and dose distributions were registered with images depicting the recurrence. Local failure (LF) was failure within the internal target volume (ITV); marginal failure (MF), as failure between the ITV and PTV plus a 10-mm margin (PTV+10mm ); and regional failure (RF) as those outside the PTV+10mm . Weekly during-treatment 4D CT 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 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=0.558). 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 (OS) rates were poorer for patients with large tumors vs. small tumors or large tumors without adaptive planning (P<0.001), the rates were similar for patients with large tumors who received adaptive planning vs. small tumors.

CONCLUSIONS: No differences in LF, MF, or RF patterns were found for IMRT vs. 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.