Abstract
BackgroundThe optimal timing of chemoradiotherapy in limited-stage small-cell lung cancer (LS-SCLC) hasn’t been established, although evidence from studies supported that patients can benefit from early radiation therapy. The purpose of this study was to quantify tumor shrinkage in response to induction chemotherapy (IC), evaluate the impact of tumor shrinkage on radiation dosimetric parameters and determine its implication for the timing of radiation therapy for patients with LS-SCLC.MethodsTwenty patients with LS-SCLC who were treated with IC followed by concomitant radiation therapy were investigated retrospectively. Ten patients received 1 cycle of IC, and 10 patients received 2 cycles of IC. Pre-IC CT imaging was coregistered with a simulation CT, and virtual radiation plans were created for pre- and post-IC thoracic disease in each case. The changes in the gross target volume (GTV), planning target volume (PTV) and dosimetric factors associated with the lungs, esophagus and heart were analyzed.ResultsThe mean GTV and PTV for all of the patients decreased by 60.9% and 40.2%, respectively, which resulted in a significant reduction in the radiation exposure to the lungs, esophagus and heart. Changes in the PTV and radiation exposure of normal tissue were not significantly affected by the number of chemotherapy cycles delivered, although patients who received 2 cycles of IC had a greater decrease in GTV than those who received only 1 cycle of IC (69.6% vs. 52.1%, p = 0.273).ConclusionsOur data showed that targeting the tumor post-IC may reduce the radiation dose to normal tissue in patients with LS-SCLC. However, the benefit to the normal tissue was not increased by an additional cycle of IC. These findings suggest that the first cycle of chemotherapy is very important for tumor shrinkage and that initiating thoracic radiation therapy at the second cycle of chemotherapy may be a reasonable strategy for timing of radiation therapy in LS-SCLC treatment.
Highlights
The optimal timing of chemoradiotherapy in limited-stage small-cell lung cancer (LS-Small cell lung cancer (SCLC)) hasn’t been established, evidence from studies supported that patients can benefit from early radiation therapy
Radiotherapy plans In some cases, the planning target volume (PTV) was very close to the spinal cord, the PTV was modified manually to meet the dose constrain of spinal cord for clinical purposes
We did not find a significant difference in the degree of reduction in PTV or radiation dose to the normal tissue between patients who received 1 cycle of induction chemotherapy (IC) and those who received 2 cycles of IC; patients who received 2 cycles of IC had a greater decrease in gross target volume (GTV) compared with those who received only 1 cycle of IC
Summary
The optimal timing of chemoradiotherapy in limited-stage small-cell lung cancer (LS-SCLC) hasn’t been established, evidence from studies supported that patients can benefit from early radiation therapy. The optimum timing for TRT has not been established, previous studies support the notion that patients can benefit from early initiation of TRT and concomitant platinum-based chemotherapy [4,5]. The first cycle of chemotherapy is the earliest time for delivering TRT. This is often accompanied by a high rate of treatment-related toxicities due to the relative extent of disease in SCLC [1,5,15], which potentially delayed subsequent chemotherapy and compromised the dose of chemotherapy, leading to prolonged overall treatment time. For patients who received TRT concurrently in the first cycle of chemotherapy, the proportion of patients completing planned chemotherapy was reported to be lower than 69% [5]
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