The multimodality management of inoperable non–small cell lung cancer (NSCLC) – from early-stage disease to locally advanced presentations – has changed substantially over the past 20 years. With the exception of small, stage I NSCLC, most nonmetastatic patients are treated with both local and systemic therapy, and there is an increasing interest in the integration of all three modalities. Radiation oncology has experienced dramatic technologic innovations over this time, which has allowed for reduced toxicity and consequent improvements in the therapeutic ratio, and in the notable case of stage I NSCLC, significantly higher cure rates.
The purpose of this chapter is to summarize the state of contemporary thoracic radiotherapy as it is used in the management of nonmetastatic, inoperable NSCLC. Inherent to this discussion are the relevant improvements in radiation therapy planning and delivery, which will be outlined in the beginning of this chapter. The remarkably improved efficacy of stereotactic body radiotherapy (SBRT) for stage I NSCLC will then be described, and this discussion will conclude with a focus on locally advanced lung cancer, highlighting three key and controversial issues that are central to the development of a treatment plan: use of chemotherapy, total radiotherapy dose, and the volume of tissue irradiated.
Brief History of Radiation Therapy
In the early era of radiotherapy, radiation planning was based on external anatomic landmarks and simple measurements of patient thickness.1 These plans were obviously crude, but the large field size presumably made up for inaccuracies in treatment planning. By the 1960s, fluoroscopic simulators, which emulated treatment machine geometry, were developed commercially, allowing radiation oncologists to design fields based on bony anatomy. Radiation planning was performed in two dimensions following the fluoroscopic simulation, in which plain radiographs were taken in the treatment position. The external contour of the patient was modeled at the isocenter of the field, and relevant internal structures were drawn on the contour by the physician, including the target and critical normal organs. The appropriate location of these structures was determined by their anatomic relationship with bony anatomy. Although the visualization of bony anatomy allowed radiation fields to become more complex, they were still fundamentally limited by an inability to know the three-dimensional (3D) location of the tumor and surrounding normal structures.
The 1970s witnessed the dawn of axial imaging, as computed tomography (CT) and magnetic resonance imaging (MRI) were developed and introduced into medical care.1 As soon as CT was developed, it became obvious to radiation oncologists and physicists that the technology could revolutionize radiation planning.2 First, the anatomic detail dramatically improved the physician's knowledge of tumor extent, and theoretically this information would lead to better target coverage. Second, the 3D dataset would allow the radiation planner to create a substantially more sophisticated beam arrangement, using computerized dosimetry and a “beam's eye-view” to optimally cover the tumor and avoid normal ...