Apparently 15% of clinics have radiation plans that pass internal quality assurance (QA) metrics but fail external audits with Imaging and Radiation Oncology Core-Houston (IROC-H). What could these small deviations that meet standard QA but not IROC-H measures mean for our most ablative treatments such as lung stereotactic body radiotherapy (SBRT)? This practical dosimetric study introduced such small errors by offsetting multileaf collimators (MLCs) over the range of ±1.0 mm for 55 lung SBRT plans. Incredibly, these tiny miscalculations in the closed direction decreased the realized delivery of radiation with a BED10 ≥100 Gy to the intended target from 95% → 27% of cases, which translated to a relative decrease in tumor control probability at two years of 21%. Tiny miscalculations in the open direction, on the other hand, lead to over a third of cases exceeding previously met dose constraints. Bottom line here is that very tight quality assurance is meaningful for procedures such as lung SBRT. | Greer, Int J Radiat Oncol Biol Phys 2022
