The Impact of Induction Chemotherapy and the Associated Tumor Response on Subsequent Radiation-Related Changes in Lung Function and Tumor Response

Purpose: To assess the impact of induction chemotherapy, and associated tumor shrinkage, on the subsequent radiation-related changes in pulmonary function and tumor response. Methods and Materials: As part of a prospective institutional review board-approved study, 91 evaluable patients treated definitively with thoracic radiation therapy (RT) for unresectable lung cancer were analyzed. The rates of RT-associated pulmonary toxicity and tumor response were compared in the patients with and without pre-RT chemotherapy. In the patients receiving induction chemotherapy, the rates of RT-associated pulmonary toxicity and tumor response were compared in the patients with and without a response (modified Response Evaluation Criteria in Solid Tumor criteria) to the pre-RT chemotherapy. Comparisons of the rates of improvements in pulmonary function tests (PFTs) post-RT, dyspnea requiring steroids, and percent declines in PFTs post-RT were compared in patient subgroups using Fisher's exact test, analysis of variance, and linear or logistic regression. Results: The use of pre-RT chemotherapy appears to increase the rate of radiation-induced pneumonitis (p = 0.009-0.07), but has no consistent impact on changes in PFTs. The degree of induction chemotherapy-associated tumor shrinkage is not associated with the rate of subsequent RT-associated pulmonary toxicity. The degree of tumor response to chemotherapy is not related to the degree of tumor response to RT. Conclusions: Additional study is needed to better clarify the impact of chemotherapy on radiation-associated disfunction.