The Study: Consensus guidelines divide vertebrae into anatomic compartments. The involved compartment and adjacent uninvolved compartments are typically covered by the target volume. This study used SBRT plans from 283 patients with 360 lesions to compare recurrence patterns according to guideline adherence or deviation. The most common regimens were 24 Gy in 2 fractions and 27 Gy in 3 fractions. They categorized three types of deviation: 1) incomplete coverage of the involved vertebral compartment, 2) omission of the adjacent involved compartment, and 3) unnecessary circumferential coverage of the entire vertebral segment when disease was present in only one or two compartments. Overall, deviation was relatively low (16.7% of sites), and many of those cases (40%) were treated at or before the time of the first consensus guideline publication. The most common type of deviation was omission of uninvolved compartments adjacent to the involved compartment (48%) followed by incomplete coverage of the involved vertebral compartment (40%). Local control was 81.1% at 1 year and 70.6% at 2 years. Targets that deviated from guidelines had inferior local control (63.0% v 85.5%). Other factors associated with recurrence were GI primary tumor, epidural disease, and extraosseous paraspinal disease. Even after adjusting for these factors, the risk of local recurrence was more than doubled with targets that deviated from guidelines. The major difference in patterns of failure was a much higher rate of marginal failure in compartments adjacent to the involved compartment (i.e. compartments undercovered when deviating from guidelines). Notably, many patients in both groups had failures that involved the epidural space (49% adherent, 58% deviant).
TBL: Stick to consensus guidelines when delineating targets for spine SBRT as there is a high risk of failure in compartments adjacent to the involved compartment.
- Chen, Radiother Oncol 2022