Status of particle therapy for lung cancer

The current standard treatment for lung cancer, the most common type of cancer worldwide, depends on disease stage. Surgery is the treatment of choice for early-stage tumors, but radiotherapy is a good option for those with early-stage tumors who cannot undergo surgery, and radiotherapy in conjunction with chemotherapy is the standard of care for locally advanced tumors. Although advances in photon (x-ray)-based radiotherapy involving three-dimensional conformal radiotherapy and intensity-modulated radiotherapy allow radiation doses to be escalated beyond the traditional limit of 60 Gy, this dose is not considered to be sufficient for tumor eradication. Moreover, the improvements in local control and survival conferred by concurrent chemotherapy come at the cost of considerable toxicity owing to inadvertent irradiation of surrounding normal tissues, and this toxicity often limits the radiation dose that can be delivered. Unfortunately for patients with locally advanced lung cancer, local control and survival remain poor. Attempts to improve clinical outcomes for patients with lung cancer have led to the use of charged particle therapy in an effort to exploit the physical properties of such particles to escalate the dose to the tumor while simultaneously limiting the dose to nearby structures, thereby enhancing the therapeutic ratio and potentially improving cancer cure rates. This review summarizes the rationale for and challenges associated with the use of charged particles for lung cancer therapy and reviews the clinical experience to date with using protons and carbon ions for early-stage and locally advanced stage non-small cell lung cancer.