Program Information
Evaluation of Improvement of Esophagus Sparing in SBRT Lung Patients with Biologically Based IMRT Optimization
X Liang*, J Penagaricano , N Paudel , X Zhang , S Morrill , P Corry , E Han , M Hardee , V Ratanatharathorn, University of Arkansas Medical Science, Little Rock, AR
Presentations
SU-E-P-47 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose: To study the potential of improving esophageal sparing for stereotactic body radiation therapy (SBRT) lung cancer patients by using biological optimization (BO) compared to conventional dose-volume based optimization (DVO) in treatment planning.
Methods: Three NSCLC patients (PTV (62.3cc, 65.1cc, and 125.1cc) adjacent to the heart) previously treated with SBRT were re-planned using Varian Eclipse TPS (V11) using DVO and BO. The prescription dose was 60 Gy in 5 fractions normalized to 95% of the PTV volume. Plans were evaluated by comparing esophageal maximum doses, PTV heterogeneity (HI= D5%/D95%), and Paddickâs conformity (CI) indices. Quality of the plans was assessed by clinically-used IMRT QA procedures.
Results: By using BO, the maximum dose to the esophagus was decreased 1384 cGy (34.6%), 502 cGy (16.5%) and 532 cGy (16.2%) in patient 1, 2 and 3 respectively. The maximum doses to spinal cord and the doses to 1000 cc and 1500 cc of normal lung were comparable in both plans. The mean doses (Dmean_hrt) and doses to 15cc of the heart (V15_hrt) were comparable for patient 1 and 2. However for patient 3, with the largest PTV, Dmean_hrt and V15_hrt increased by 62.2 cGy (18.3%) and 549.9 cGy (24.9%) respectively for the BO plans. The mean target HI of BO plans (1.13) was inferior to the DVO plans (1.07). The same trend was also observed for mean CI in BO plans (0.77) versus DVO plans (0.83). The QA pass rates (3%, 3mm) were comparable for both plans.
Conclusion: This study demonstrated that the use of biological models in treatment planning optimization can substantially improve esophageal sparing without compromising spinal cord and normal lung doses. However, for the large PTV case (125.1cc) we studied here, Dmean_hrt and V15_hrt increased substantially. The target HI and CI were inferior in the BO plans.
Contact Email: