In the bone.

Top Line: When treating oligometastatic cancer with stereotactic body radiation (SBRT), it’s fairly common to have at least one site that’s a non-spine bone metastasis (NSBM).

The Study: So, what’s the best way to approach such targets? We’ve seen an MDACC trial that showed improved pain control from 12-16 Gy x 1 compared to 8 Gy x 1 for NSBM. Here we have a nice survey of world experts describing their approaches. They were asked to generate targets and propose fractionation schemes for a series of cases involving long bones, pelvic bones, and non-spine axial skeleton (ribs, sternum, scapula, clavicle). Just over half the experts routinely used MRI to delineate targets while a quarter selectively used MRI, and the rest routinely relied on CT alone. As a result, there was considerable variability in target volumes. 35 Gy in 5 fractions was the most frequently chosen fractionation scheme. The other most common schemes were 30 Gy/5, 30 Gy/3, and 20 Gy/1. And a solid third of experts used a simultaneous integrated boost (SIB) approach to their targets. The SIB approach typically employed these SBRT doses with a lower, more conventional dose to a larger surrounding target. Importantly, depending on the site, not just any fractionation scheme would do. Factors such as prior treatment, weight-bearing, and severe cortex erosion heavily influenced recommendations. So while almost any scheme was deemed appropriate in the scapula, some regimens (mainly single fraction or high BED) were deemed less so for targets in the humerus, femur, or acetabulum. Lastly, there was a fairly strong consensus against super high-BED regimens such as 50 Gy/5. 

TBL: Non-spine bone SBRT deserves just as much care in planning and delivery as other targets. | Nguyen, Pract Radiat Oncol 2020