Shrinkage of locally advanced non-small-cell lung cancers in response to induction chemotherapy: implications for radiotherapy treatment planning.

PURPOSE

To quantify the impact that changes in tumor volume after induction chemotherapy have on radiotherapy treatment planning for locally advanced non-small-cell lung cancer.

METHODS AND MATERIALS

An analysis of coregistered pre- and postchemotherapy tumor volumes in a Phase II study of induction chemotherapy delivered before radical radiotherapy.

RESULTS

Using the Response Evaluation Criteria In Solid Tumors measurement, 35% of patients had a partial response and 62% had stable disease after chemotherapy. Conversely, volumetric decreases in tumor size were seen in 95% of patients. Mean decreases in gross tumor volume and planning target volume were 37% and 26%, respectively. Using the smaller postchemotherapy tumor volume to plan radiotherapy treatment leads to a mean decrease in volume of lung receiving 20 Gy or greater of 3% (p < 0.005). Targeting the postchemotherapy volume also results in the delivery of a significant, although inhomogeneous, incidental dose of radiation to the rind of tissue formed around the shrinking tumor. Disease shrinkage is anisotropic, with greater displacements observed along anterior, posterior, and lateral margins. After chemotherapy, there is measurable blurring of the tumor's radiologic edge.

CONCLUSIONS

Modest decreases in tumor volume that are not reflected by the Response Evaluation Criteria In Solid Tumors measurement occur in most patients. Although targeting the postchemotherapy tumor may decrease lung toxicity, the magnitude of the benefit is small. Because this strategy runs the risk of increasing the marginal recurrence rate, it should be used with caution. Quantification of tumor shrinkage and margin blurring permits more accurate reconstruction of the prechemotherapy target volume.