Introduction: For patients with stage III non-small cell lung cancer treated with induction chemotherapy (ICT), delayed initiation of subsequent radiotherapy (RT) may allow for repopulation in the interval between treatment modalities and during the early phase of RT. We quantified the impact of postinduction RT timing by evaluating the pace of tumor regrowth.
Methods: Institutionally approved retrospective review identified 21 analyzable patients with stage III non-small cell lung cancer who had platinum-based ICT followed by RT+/- chemotherapy from 2002 to 2009. Radiographic response was determined by RECIST criteria and the volume of the single largest tumor mass on the pre-ICT, post-ICT, and RT-planning computed tomography scans.
Results: After ICT, the median percent volume change from pre-ICT baseline was -41% (range -86 to +86%). By the RT-planning computed tomography scan, the median percent volume change from the post-ICT timepoint was +40% (range -11 to +311%) and the median volume change was +20 ml (range -4 to 102 ml); these changes were significant (p = 0.0002). Similar results were seen for tumor diameter. A correlation was observed between the amount of delay and degree of regrowth for percent volume (p = 0.0006) and percent diameter change (p = 0.003). A delay greater than 21 days produced greater increases in percent volume change (p = 0.002) and percent diameter (p = 0.055) than lesser delays.
Conclusions: After ICT, tumor regrowth can occur within a few weeks. Radiation treatment planning should begin as soon as possible after the administration of ICT to maximize the benefits of cytoreduction.