Abstract
PurposeTo investigate the influence of induction chemotherapy (ICT) on dosimetric outcomes in patients with inoperable non-small cell lung cancer (NSCLC) treated with definitive chemoradiation (CRT).Materials and methods30 patients with inoperable stage II-III NSCLC treated with 2–4 cycles of ICT followed by definitive CRT to ≥ 60 Gy were selected. Tumor response to chemotherapy was scored by RECIST criteria. Treatment plans based on tumor extent prior to chemotherapy were generated based on equivalent planning constraints and techniques as the original post-chemotherapy plans. Dosimetric parameters predictive of toxicity for lung, esophagus, heart, and spinal cord were compared amongst the pre- and post-ICT plans.ResultsThe majority of patients (70%) experienced an overall reduction in GTV size between the pre-ICT imaging and the time of simulation. Comparing pre-and post-ICT diagnostic imaging, 5 patients met the RECIST criteria for response, 23 were classified as stable, and 2 experienced disease progression on diagnostic imaging. Despite a significantly reduced GTV size in the post-ICT group, no systematic improvements in normal tissue doses were seen amongst the entire cohort. This result persisted amongst the subgroup of patients with larger pre-ICT GTV tumor volumes (>100 cc3). Among patients with RECIST-defined response, a significant reduction in lung mean dose (1.9 Gy absolute, median 18.2 Gy to 16.4 Gy, p = 0.04) and V20, the percentage of lung receiving 20 Gy (3.1% absolute, median 29.3% to 26.3%, p = 0.04) was observed. In the non-responding group of patients, an increased esophageal V50 was found post-chemotherapy (median 28.9% vs 30.1%, p = 0.02).ConclusionsFor patients classified as having a response by RECIST to ICT, modest improvements in V20 and mean lung dose were found. However, these benefits were not realized for the cohort as a whole or for patients with larger tumors upfront. Given the variability of tumor response to ICT, the a priori impact of induction chemotherapy to reduce RT dose to normal tissue in these patients is minimal in the setting of modern treatment planning.
Highlights
In the treatment of non-small cell lung cancer (NSCLC), induction chemotherapy (ICT) is commonly used as a means of cytoreduction to reduce subsequent radiotherapy field size or to convert a previously unresectable lung tumor to resectability
For patients classified as having a response by Response Evaluation Criteria for Solid Tumors (RECIST) to ICT, modest improvements in V20 and mean lung dose were found
Given the variability of tumor response to ICT, the a priori impact of induction chemotherapy to reduce RT dose to normal tissue in these patients is minimal in the setting of modern treatment planning
Summary
In the treatment of non-small cell lung cancer (NSCLC), induction chemotherapy (ICT) is commonly used as a means of cytoreduction to reduce subsequent radiotherapy field size or to convert a previously unresectable lung tumor to resectability. The actual impact, of this approach in improving dosimetric parameters to normal tissues using modern techniques in clinical practice is not well studied. ICT has not been shown to confer survival advantage in a sequential approach with concurrent chemoradiotherapy (CRT) and confers added toxicity and treatment time [1,2]. Given these costs, we sought to investigate dosimetric impact of ICT in 30 sequential patients treated with a homogeneous and well-accepted regimen of ICT followed. The effects of ICT on target and normal tissue dosimetric variables were quantified in this population by comparing treatment plans generated from pre- and postchemotherapy volumes, both as an entire cohort and stratified by RECIST response
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