Matching between Clinical and Dosimetric Results in Comparing Intensity Modulated Radiotherapy with Three-Dimensional Conformal Radiotherapy in Locally Advanced Lung Cancer

Abstract

Background Radiation therapy plays an essential role in the treatment of locally advanced lung cancer, but it inevitably leads to incidental and unnecessary dose to critical organs, including the lung, heart, and esophagus. Objective A dosimetric study to compare 3D CRT to IMRT in locally advanced lung cancer as regards normal tissue irradiation and target coverage using COSI & modified COSI indices, DVH, homogeneity index, conformity index, target coverage index. Also to evaluate acute and late toxicity of esophagus, heart and lung in three-dimensional conformal radiotherapy and intensity modulated radiotherapy, in patients with locally advanced lung cancer who received definitive concurrent chemo-radiation or sequential chemo-radiation according to Common Terminology Criteria for Adverse Events (CTCAE) version 5.0. Patients and Methods 20 patients were selected to participate in our retrospective study from 2014 till 2019. They were recruited from bronchogenic cancer clinic, clinical oncology department in Ain Shams University Hospitals using a convenient sampling method. Diagnosis of NSCLC or SCLC was confirmed histologically and further radiological assessment for TNM staging was performed. All patients where 18 years old or older and were prescribed for either combined or sequential chemoradiotherapy for treatment of locally invasive lung cancer with ECOG PS equal or less than 2. They received 3D CRT of total 60 Gy. On the same CT contour defined for 3D CRT another plan was done for IMRT by computer based inverse planning with specific dose constrains to surrounding organs. Results In our study IMRT technique helped in sparing doses delivered to heart, lung & esophagus in comparison with 3D CRT, but it was statistically significant for the lung only with p-value = 0.003. As regard the dosimetric indices IMRT showed better target coverage, dose homogenity & dose conformity in comaparison with 3D CRT, but it was statistically significant for CI with p-value= 0.028. Using the COSI & mCOSI also was in favor of IMRT but it was stastistically significant in mCOSI with pvalue=0.023 Conclusion IMRT showed superior outcomes as regards delivered doses (both to target and at-risk organs) compared to the conventional 3D CRT achieving the main purpose for patients with locally advanced lung cancer receiving chemoradiothrapy which is better target volume coverage and less unnecessary dose to at-risk nearby vital organs. As IMRT spares OAR it’s expected that clinical toxicity noticed with 3DCRT will be less thus, more tolerability to CCRT.