Abstract
External-beam radiotherapy, often combined with chemotherapy, is the treatment of choice for locally advanced inoperable lung cancer. Locoregional control and disease-free survival, however, are limited with the current clinically applied treatment strategies. An important factor is the inability to deliver sufficiently high dose levels, mainly caused by the fact that the limited geometrical accuracy impedes further dose escalation owing to risk of complications. Higher conformality of the planned dose distributions and higher levels of accuracy in radiotherapy delivery reduces the amount of normal tissues irradiated, such that the tumor and pathologic lymph nodes can be safely irradiated to higher doses. In this review we describe recent developments in imaging, treatment planning and treatment delivery that have the potential to increase the efficacy of lung cancer radiation therapy. Respiratory-correlated imaging techniques eliminate respiratory-induced artifacts and produces 4D scans representing the patient's anatomy (CT) and biology (18-fludeoxyglucose [(18)FDG]-PET) over the respiratory cycle. Moreover, (18)FDG-PET scans provide information on the heterogeneous tumor characteristics. Intensity-modulated radiotherapy planning techniques produce highly conformal dose distributions tailored to the patient-specific respiratory motion patterns and, possibly, tumor characteristics. Image-guided radiotherapy utilizes repetitive imaging in the treatment room to measure and correct tumor misalignments. Finally, adaptive radiotherapy monitors the patient over the course of treatment and allows for adaptive treatment-plan modifications to individualize the treatment to the observed patient-specific changes. These techniques thus allow the delivery of higher doses of irradiation that yield a greater probability of complete response, higher tumor control and better survival in irradiated lung cancer patients.