Margin of error.

Top Line: Clinical target volumes for definitive stereotactic ablative radiation (SABR) for early-stage non-small cell lung cancer (NSCLC) could stand to be better defined.

The Study: As opposed to conjecture, this French study went straight to the source: pathologic specimens. The “microscopic extent” from gross tumor (i.e., visible to the naked eye) to the farthest cancer cell (detectable per microscope) was measured for 112 adenocarcinomas and 42 squamous cell carcinomas (SCC) ≤4 cm undergoing upfront resection between 2013-2018. In order to cover 95% of the farthest microscopic extent of specimens, a CTV margin of 4.4 mm would be required for SCC and 2.9 mm for adenos. Interestingly, farthest microscopic extent could be distilled even further by the extent of tumor infiltrating lymphocytes in SCC, where CTV margins of 5.0 mm for 0–10%, 2.1 mm for 20–40% and 0 mm for 50–90% would be required to cover 95% of cases, and preseconce of COPD in adenos, where CTV margins of 3.7 mm with COPD and 2.3 mm without COPD would be required. Finally, while there was no detectable correlation between tumor size and farthest microscopic extent for adnoes, a CTV margin of 4.9 mm is required to cover 95% of SCC >1.5 cm versus only 0.7 mm for SCCs ≤1.5 cm.

TBL: Useful extent of CTV margins in definitive SABR for early-stage NSCLC may be informed by histologic subtype, tumor size, extent of TILs, even presence of COPD. | Schmitt, Cancers 2022