Analysis of V20 and Radiation Pneumonitis on SWOG 0023: A Phase III Trial of Concurrent Chemoradiation and Docetaxel Consolidation in Stage III Non-small Cell Lung Cancer
SWOG 0023 was a phase III trial evaluating the use of radiation therapy given with cisplatin and etoposide chemotherapy, followed by docetaxel chemotherapy, and then gefitinib or placebo for maintenance, in patients with inoperable stage IIIA or stage IIIB non-small cell lung cancer. This analysis of the data from SWOG 0023 looked to evaluate the risk and rates of pneumonitis (inflammation of the lung tissue) in the patients who received radiation. A measurement called V20 (% of the total lung volume receiving ?20 Gy dose of radiation) has previously been found to correlate with the development of pneumonitis. A V20 of <35% was recommended but not required for patients enrolled in the trial.
Of the 444 patients for whom radiation details are known, V20 was found to exceed 35% in 18% of patients. V20 was found to be significantly associated with the subsequent development of grade 3 (out of 4) pneumonitis. V20 > 35% was found to be significantly associated with the development of grade 3 (out of 4) esophagitis. Survival for patients with V20 > 35% was found to be significantly worse compared to those with a lower V20. Caution must be used in interpreting this data because the study was not designed to determine survival. Furthermore, this difference may have been due to a larger tumor size, and thus a necessarily larger V20.
V20 is increasingly being used in treatment planning in an effort to decrease the incidence of radiation-induced pneumonitis. However, the measure does not provide information on the "quality" of the lung receiving radiation. The volume of lung able to tolerate a given amount of radiation may certainly differ between that of a "never-smoker" and that of a patient with a long-standing history of heavy tobacco use who has a large amount of non-functioning lung. A measure or tool that would assist in estimating the allowable V20 for an individual patient, based on the "quality" of that patient's lungs, would be very useful.