SU-E-T-759: Evaluation of Pencil Beam Convolution and Anisotropic Analytical Algorithm in Stereotactic Lung Irradiation

Abstract

Purpose: To evaluate dose distributions in stereotactic body radiation therapy (SBRT) treatment plans for lung tumors calculated with pencil beam convolution (PBC) algorithm with modified Batho power law (MBPL) against heterogeneity corrected anisotropic analytical algorithm (AAA) of the Varian Eclipse treatment planning system. Methods: The 4D CT image data from twenty patients with low stage non-small cell lung cancer were used to create treatment plans with 5 to 7 fields 6 MV coplanar non-opposing beams. Internal target volumes (ITVs) were given a 0.7 cm margin to create planning target volumes (PTVs). Plans were generated with PBC (MBPL) for tissue heterogeneity and optimized with a prescribed dose of 60 Gy in 3 fractions to at least 95% of the PTV. These optimized plans were recalculated with AAA, with identical beam arrangements, fluences and monitor units, to generate comparison plans. Results: The AAA plans had lower average minimum, mean and maximum PTV doses by 17%, 8.2% and 2.1% respectively compared to PBC plans. The average dose to 95% of the PTV volume (D95) for AAA plans was lower by ∼14% compared to PBC. The average percentage of uninvolved lung volume receiving minimum doses of 10 Gy (V10) and 20 Gy (V20) was below 10.3% and 5.3% for both PBC and AAA plans. The AAA plans had lower average mean and maximum uninvolved lung dose by 8.6% and 8.9% respectively compared to PBC plans. Conclusions: The average D95 of 51.6 Gy calculated with AAA compared to 60 Gy with PBC in this study agrees well with the recent suggestion by the quality assurance working group of phase III Rosel study of prescription dose reduction of 10% from 60 Gy to 54 Gy when utilizing AAA instead of PBC.