It was a pleasure to read the manuscript written by Dr. Decker and colleagues regarding the role of radiation therapy in unresectable lung cancer. However, the reader should be advised that a great deal of this manuscript, as it pertains to radiation dose, confuses the issue by including stage I through stage III lung cancer. The most common clinical situation in radiation oncology concerns the management of patients with stage III disease. Most of the literature regarding radiation dose escalation comes from patients with regionally advanced, nonmetastatic, non-small-cell lung cancer (NSCLC). It is unclear whether data abstracted from the management of stage III patients is relevant to the management of those with relatively small peripheral lesions and no clinical evidence of metastatic disease.Does biology trump anatomy? Radiation oncologists have long maintained that dose escalation to the tumor volume in patients with stage III disease will impart an improvement in local control that will result in an improvement in survival. Theoretically this represents an attractive hypothesis, but there is little level 1 evidence to support this conclusion. The exception to this statement is the Saunders paper referenced in Dr. Decker's review. The reader should also be aware that the data from Great Britain includes patients with stage I and II disease and may not necessarily be representative of stage III lung cancer patients treated in the United States.
Improved Survival in Stage III Lung Cancer
The median survival for regionally advanced NSCLC has improved steadily since 1973, when the Radiation Therapy Oncology Group (RTOG) conducted its first dose-escalation trial. However, it is unclear that radiation dose escalation has contributed to the improvement in median survival. Median survival has improved from approximately 10 to 18 months, but the cause for this improvement is multifactorial.
The routine inclusion of systemic therapy into initial treatment in the management of stage III disease has undoubtedly contributed to an improvement in median survival. The inclusion of concurrent chemoradiation therapy into the management of patients with stage III disease has resulted in an increase in acute toxicity. As the toxicity of initial treatment increases, patient selection for these aggressive treatment regimens narrows. The resulting "Will Rogers effect" has also contributed to the observed improvement in median survival seen in recent cooperative group trials.Clearly, in regionally advanced NSCLC, we have improved the median survival and decreased radiation toxicity with sophisticated treatment planning. Whether this supports the theoretical benefits of dose escalation, however, remains unclear.
Radioablation in Stage I NSCLC
The management of potentially operable lung cancer with external-beam radiation therapy represents an interesting chapter in the evolution of radiation oncology. Scientific developments related to equipment hardware, imaging, and treatment delivery software have contributed substantially to our ability to deliver finely directed radiation. Peripheral lung lesions represent a unique technical challenge that potentially lends itself to the adaptation of this new technology. Small peripheral lung lesions represent a moving target surrounded by relatively easily damaged tissue. Patients with smoking-induced cancer are functionally challenged at diagnosis and can suffer substantially from radiation injury.
As outlined in the review, the incorporation of these technologic advances in the management of lung cancer has resulted in clinical research into frequently administered, finely focused radiation therapy delivered to peripheral lesions. The biologic doses of radiation in most series are more correctly termed "radioablation," representing doses that far exceed what is normally delivered with standard technology. Although theoretically attractive and preliminarily encouraging, one must be aware that no level 1 evidence suggests that dose escalation is either required or represents an improvement over surgical techniques.