Secret sauce.

Despite the straightforward dose/fractionation schemes and organ-at-risk constraints for lung SBRT, the details of treatment planning are highly variable among providers and institutions. Here’s a great paper outlining the specific details of the treatment planning process for lung SBRT at three academic centers. Consistent across centers was the use of supine, arms up positioning, 4DCT simulation with the use of the average dataset for planning, the use of a 5 mm PTV margin, and prescription normalization to D95%≥100%. But then things diverge. One of the three centers uses a 2-3 mm CTV margin. Typical prescriptions also varied. The typical prescription for a peripheral tumor for each center was: 1) 48 Gy in 4 fractions, 2) 50Gy in 4 fractions with 60 Gy SIB, and 3) 54 Gy in 3 fractions (or 48 Gy in 4 fractions adjacent to the chest wall). The typical prescription for central tumors for each center was: 1) 48 Gy in 4 fractions, 2) 50 Gy in 4 fractions or 70 Gy in 10 fractions, and 3) 50Gy in 5 fractions. There was also considerable variation in intra-target dose heterogeneity. Center 1 prescribed a 60 Gy in 4 fraction SIB to the GTV and required the maximum dose to be between 115% and 150%. Center 2 used no maximum dose constraint, and Center 3 kept maximum dose <115%. Only Center 1 utilized the RTOG R50 and conformity index in their planning goals. | De Leo, Pract Radiat Oncol 2022