Evaluation of the effect of cone beam computed tomography (CBCT) system in adaptive radiotherapy (ART) lung plans

Target volume and healthy lung tissue changes during radiotherapy may effect lung tissue-toxicity for patients with lung cancer. Shrinkage or upsizing of the tumor size may be seen during the course of conventionally fractionated radiotherapy course. Pre-radiotherapy Computed Tomography (CT) and Cone Beam CT (CBCT) images taken during-radiotherapy may be effectively used for Adaptive Radiotherapy (ART) of lung cancer patients. However, the reasonable time interval between CBCT imaging is important for consideration of tumor volume changes to achieve normal tissue sparing. CBCT of twenty non-small cell lung cancer patients were retrospectively examined to evaluate the effectivity of 10th, 20th and 30th imaging days in establishing a better tumor coverage and healthy tissue sparing for shrinkage and upsizing conditions. The baseline treatment plan (pCT), 1st adaptive treatment plan (pCBCT1), 2nd adaptive treatment plan (pCBCT2), 3rd adaptive treatment plan (pCBCT3) were analyzed to determine changes in target and critical organs. Wilcoxon signed-ranks test with Bon Ferroni correction was performed to determine which adaptive plan was different. A significant difference was found between pCT to pCBCT2; pCT to pCBCT3; pCBCT1 to pCBCT2; pCBCT1 to pCBCT3 in adaptive treatment plans for Lung-GTV (V20) and Lung-GTV (V5) (p value ≤ 0.05). A significant difference was found between pCT to pCBCT2; pCT to pCBCT3: pCBCT1 to pCBCT3 in adaptive treatment plans for Lung-GTV (MLD), Heart V (30), Heart V (45), Heart (mean), Esophagus (mean) and Brachial plexus (max) (p value ≤ 0.05). A significant difference was found between pCT to pCBCT1; pCT to pCBCT2; pCT to pCBCT3: pCBCT1 to pCBCT3 in adaptive treatment plans for Cord (max) (p value ≤ 0.05). A significant difference was found between pCT to pCBCT3 in adaptive treatment plans for Heart V (60) (p value ≤ 0.05) (Spss version 22). CBCT serves as an effective imaging tool for normal tissue sparing by adaptive lung cancer radiotherapy.