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.