Selective nodal irradiation of regionally advanced non‐small‐cell lung cancer with proton therapy and IMRT: A dosimetric comparison

OBJECTIVES: Evaluate the dosimetric impact of selective/elective nodal treatment with dose-escalated radiotherapy for regionally advanced non-small-cell lung cancer (NSCLC) using proton therapy (PT) or intensity-modulated radiotherapy (IMRT). METHODS: Five consecutive patients with regionally advanced NSCLC underwent treatment planning for high-dose involved-field (IF) treatment (positron emission tomography-positive gross disease) with or without selective/elective nodal irradiation, defined as the extended field (EF). Four treatment plans were developed for each patient: i) IMRT to treat IF to 74 Gy (IFrT); ii) IMRT to treat high-risk nodes to 44 Gy and IF to 74 Gy (EFrT); iii) PT to treat IF to 74CGE (IFpT); and iv) PT to treat high-risk nodes to 44CGE and IF to 74CGE (EFpT). High-risk nodes were defined as mediastinal, hilar, and supraclavicular lymph node stations adjacent to foci of PET-positive gross disease. The IMRT and PT plans were isoeffective. Dose to organs at risk (OARs), including the lung, esophagus, heart and spinal cord, were evaluated. RESULTS: The average IF clinical target volume (CTV) was 397 cc (344-428), while the average EF CTV was 642 cc (530-753 cc). Comparing IMRT with PT, mean lung dose reduced 3.4 Gy/CGE and 3.7 Gy/CGE; lung V20 reduced 4% and 5% for EF and IF, respectively. CONCLUSIONS: Selective/elective nodal irradiation with protons reduces normal-lung exposure compared to selective/elective nodal irradiation with IMRT.