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The Optimal A-Value in the Equivalent Uniform Dose Model to Predict Radiation-Induced Proximal Bronchial Tree Toxicity in Patients with Non-Small Cell Lung Cancer

H Ai

H Ai1*, W Wang2 , M Matuszak3 , J Jin4 , F Kong5 , (1) Indiana University School of Medicine, Indianapolis, IN, (2) Indiana University School of Medicine, Indianapolis, INDIANA, (3) University of Michigan, Ann Arbor, MI, (4) Indiana University- School of Medicine, Indianapolis, IN, (5) Indiana University- School of Medicine, Indianapolis, IN


SU-I-GPD-T-99 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: We have found that the dosimetry of proximal bronchial tree (PBT) is a significant risk factor for radiation-induced PBT toxicity in patients treated with radiotherapy for non-small cell lung cancer (NSCLC). This study aimed to determine the optimal a-value in the equivalent uniform dose (EUD) model that best predicts PBT toxicity.

Methods: 100 NSCLC patients treated with definitive thoracic radiotherapy were included in this study. PBT and PBT wall (PBTW) were consistently contoured following RTOG guideline. EUDs of PBT and PBTW were calculated from their corresponding dose volume histogram (DVH) using a power-law based model with variable a-values (integer from 1 to 40). Receiver operator characteristic curves (ROC) with areas under the ROC (AUC) were generated to assess the optimal a-value and to compare with other single-point DVH parameters such as V30 and V75.

Results: V75 and V80 were the optimal single-point DVH parameters for PBT and PBTW, with AUC = 0.660 and 0.690, respectively. The optimal a-value was 6 for EUD of PBT with the maximum AUC =0.712. The optimal a-value was 5 for EUD of PBTW, with the maximum AUC =0.710. The AUC was at a relatively stable value (0.705-0.708) when a-value further increased from 10 to 40.

Conclusion: EUD appears to be a better dosimetry parameter than the single-point parameter. The optimum a-value is about 5-6 for PBT and PBTW, suggesting that PBT or PBTW is a series organ.

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