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Comprehensive Investigation of Dose Calculation for Lung Stereotactic Ablative Radiation (SABR): Effects of Tumor Size and Location and Clinical Recommendations

S Devpura

S Devpura*, M Siddiqui, D Liu, D Chen, H Li, S Kumar, M Ajlouni, B Movsas, I Chetty, Henry Ford Health System, Detroit, MI

TH-A-137-10 Thursday 8:00AM - 9:55AM Room: 137

Purpose: To determine the influence of tumor size and location on dose calculation accuracy of 6 different algorithms in treatment of lung cancer patients using SABR.

Methods: The study consisted of 135 patients with non-small-cell lung cancer previously treated using SABR treatment plans created using a 1-D pencil beam algorithm (1-D equivalent-path-length (1D-EPL) in iPlan). The dose regimen was 12Gy in 4 fractions. Dose was recomputed using six clinically commissioned dose calculation algorithms; 3-D pencil beam (3D equivalent-path-length (3D-EPL) in Eclipse), anisotropic analytical algorithm (convolution/superposition type, AAA in Eclipse), collapsed cone convolution (convolution/superposition type CCC in Pinnacle), AcurosXB (Eclipse), and Monte Carlo (MC iPlan). Location of the lung tumors was categorized as follows: island-type peripheral tumors surrounded by lung tissues (lung-island; N=39), tumors attached to the chest-wall (lung-wall; N=44), and tumors located in the central area (lung-central; N=52). Average irradiated field size (FS) was subdivided into three groups, between 3-5, 5-7, and 7-10 cm.

Results: For lung-island tumors, D95 values relative to the 1D-EPL (with which the patients were treated) were 81.6±4.4%, 81.4±5.8%, 78.4±6.6%, and 81.4±5.8% for AAA, CCC, AcurosXB, and MC algorithms respectively. For lung-wall tumors, dose values for AAA, CCC, AcurosXB, and MC were 86.8±4.9%, 87.4±5.6%, 84.7±6.6%, and 86.9±5.7%, while respective values for lung-central tumors dose values were 86.1±5.9%, 86.5±6.6%, 85.0±7.0%, and 86.7±6.2%. Considering the effects of both tumor size and location, the lowest D95 values (relative to 1D-EPL) were observed for the smallest lung-island tumors (3-5 cm): 80.2±4.3%, 80.0±6.0%, 76.6±6.9%, and 79.7±5.9% for AAA, CCC, AcurosXB, and MC algorithms, respectively. The smallest dose difference was observed for the largest tumors (7-10 cm) for lung-central tumors.

Conclusion: For small lung tumors located peripherally, treated using SABR, EPL-based algorithms must be used with extreme caution. Under these circumstances even convolution/superposition and MC-based algorithms show larger variation in PTV dose.

Funding Support, Disclosures, and Conflict of Interest: Please refer to the supporting document.

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