Consensus Statement on Proton Therapy in Early-Stage and Locally Advanced Non-Small Cell Lung Cancer

Abstract

Radiation dose escalation has been shown to improve local control and survival in patients with non-small cell lung cancer in some studies, but randomized data have not supported this premise, possibly owing to adverse effects. Because of the physical characteristics of the Bragg peak, proton therapy (PT) delivers minimal exit dose distal to the target volume, resulting in better sparing of normal tissues in comparison to photon-based radiation therapy. This is particularly important for lung cancer given the proximity of the lung, heart, esophagus, major airways, large blood vessels, and spinal cord. However, PT is associated with more uncertainty because of the finite range of the proton beam and motion for thoracic cancers. PT is more costly than traditional photon therapy but may reduce side effects and toxicity-related hospitalization, which has its own associated cost. The cost of PT is decreasing over time because of reduced prices for the building, machine, maintenance, and overhead, as well as newer, shorter treatment programs. PT is improving rapidly as more research is performed particularly with the implementation of 4-dimensional computed tomography-based motion management and intensity modulated PT. Given these controversies, there is much debate in the oncology community about which patients with lung cancer benefit significantly from PT. The Particle Therapy Co-operative Group (PTCOG) Thoracic Subcommittee task group intends to address the issues of PT indications, advantages and limitations, cost-effectiveness, technology improvement, clinical trials, and future research directions. This consensus report can be used to guide clinical practice and indications for PT, insurance approval, and clinical or translational research directions.

Fig. 1.

Comparison of intensity modulated proton therapy (IMPT) versus passive scattering proton therapy (PSPT) and volumetric intensity modulated arc therapy (VMAT) in stage III non–small cell lung cancer. The IMPT plan achieves the best sparing of all critical structures. PSPT spares more of the heart and contralateral lung but not the esophagus ipsilateral lung, lung mean dose, or volume receiving a dose of 20 Gy or higher as compared with VMAT. Abbreviations: CTV = clinical target volume; GTV = gross tumor volume; PTV = planning target volume.

Fig. 2.

Comparison of proton- versus proton-based stereotactic body radiation therapy in a centrally located lesion in stage I non–small cell lung cancer. As compared with photon therapy, proton therapy spares more of the bronchial tree, lung, major vessels, heart, and spinal cord.