Ablative radiation to the sacrum differs from treatment to more proximal spine in a big way, namely target lesions occurring in much larger contiguous bone segments. This has led to very generous contouring guidelines and noted increases in local failure when skimping on said generous volumes. A pattern-of-failure analysis of 48 local recurrences following ablative radiation to the sacrum, 11(23%) occurred outside of the target but within bony sectors that would have been included per published guidelines. Nonadherent contours were associated with higher failure rates in both involved (37% vs. 18%) and adjacent (23% vs. 2%) at-risk sectors. Put another way, the widely-recognized phenomenon of metastatic bone lesions harboring microscopic disease in notoriously wide swaths of contiguous bone becomes a moot point for discrete vertebral bodies of the spine in a way it does not for the large bony sacrum. | Moore-Palhares, Pract Radiat Oncol 2026
