PROTON STEREOTACTIC BODY RADIATION THERAPY FOR CLINICALLY CHALLENGING CASES OF CENTRALLY AND SUPERIORLY LOCATED STAGE I NON-SMALL-CELL LUNG CANCER

Purpose: To minimize toxicity while maintaining tumor coverage with stereotactic body radiation therapy (SBRT) for centrally or superiorly located stage I non-small-cell lung cancer (NSCLC), we investigated passive-scattering proton therapy (PSPT) and intensity-modulated proton therapy (IMPT). Methods and Materials: Fifteen patients with centrally or superiorly located (within 2 cm of critical structures) stage I NSCLC were treated clinically with three-dimensional photon SBRT (50 Gy in 4 fractions). The photon SBRT plan was compared with the PSPT and IMPT plans. The maximum tolerated dose (MTD) was defined as the dose that exceeded the dose volume constraints in the critical structures. Results: Only 6 photon plans satisfied the >95% planning target volume (PTV) coverage and MTD constraints, compared to 12 PSPT plans (p = 0.009) and 14 IMPT plans (p = 0.001). Compared with the photon SBRT plans, the PSPT and IMPT plans significantly reduced the mean total lung dose from 5.4 Gy to 3.5 Gy (p < 0.001) and 2.8 Gy (p < 0.001) and reduced the total lung volume receiving 5 Gy, 10 Gy, and 20 Gy (p < 0.001). When the PTV was within 2 cm of the critical structures, the PSPT and IMPT plans significantly reduced the mean maximal dose to the aorta, brachial plexus, heart, pulmonary vessels, and spinal cord. Conclusions: For centrally or superiorly located stage I NSCLC, proton therapy, particularly IMPT, delivered ablative doses to the target volume and significantly reduced doses to the surrounding normal tissues compared with photon SBRT. (C) 2011 Elsevier Inc.