MO‐A‐137‐11: How Successful Are We in Meeting SBRT Planning Goals? A Multi‐Institutional Study

Abstract

Purpose: To assess the variability in treatment planning of stereotactic body radiotherapy (SBRT) of lung lesions, a multi‐institutional planning comparison study was performed. Methods: A total of 150 patients receiving lung SBRT treatments in five different institutions were reviewed. Treatment plans were generated using Varian/Eclipse™ (82), CMS/Xio™ (53) and Cyberknife/Multiplan™ (15) systems. Most tumors were located peripherally (126/150) and in right lung (82/150). Various dose fractionations were used: 3x18Gy (5 cases), 3x20Gy (13), 4x12Gy (18), 4x12.5Gy (9), 5x10Gy (65), 5x12Gy (38), and 5x8or9Gy (2). The following planning criteria derived from RTOG trials and literature were used to evaluate the 4 or 5 fraction SBRT plans (133 cases): PTV‐V100>=95°/o, PTVV95>=99%, conformality index (CI‐100%) <1.2, CI‐50% isodose <4 for PTV>50cc or <5 for PTV<50cc, total lung‐ITV: V20Gy<10%, V12.5Gy<15%, V5Gy<37%, contralateral lung V5Gy<26%, cord: maximum<25 Gy, D0.25cc<22.5Gy, esophagus: max<30Gy, D5cc<27.5Gy, trachea/bronchus maximum<40Gy, heart & great vessels maximum<45Gy. The mean, standard deviation (±) and dosimetric criteria pass rates (PR) were reported. Results: The median PTV volume was 27.0cc (range:3.8/188.9cc). The mean PTV‐V100 was 96.0% (±3.6, PR:87.1%). The mean PTV‐V95 was 99.4% (±2.1, PR:90.2%) and the mean CI‐100% was 1.16 (±0.18, PR:74.0%). The mean CI‐50% was 4.14 (±0.67, PR:46.4%) for PTV>50cc (28 cases) and 7.36 (±3.36, PR:29.4%) for PTV<50cc (102 cases). The planning criteria were met for all the critical structure such as lung, heart, cord, esophagus, and trachea for at least 90% of the patients. The mean of all OAR criteria PR was 97.7% for peripheral and 88.6% for central lesions. Conclusion: Five fraction regimens were the most common lung SBRT fractionation (70%). Among the various parameters that were used to evaluate the SBRT plans, the CI‐100% and CI‐50% were the most challenging criteria to meet. Although the OAR PRs were higher among all cases, their proximity to the PTV was a significant factor.