Nonspine Bone Metastases SBRT Practice Patterns
ForNonsurgical nonspine bone metastases considered for SBRT
TL;DR35 Gy/5 most often chosen (29/99 responses); 40 Gy/5 acceptable to 8 or 9 of 9 experts wherever listed; every schedule BED ≤100 Gy10.
The site-specific rejections are the RT read: 20 Gy/1 lost majority support in the humerus, acetabulum and femur cases, and 50 Gy/5 in the humerus and acetabulum, while 40 Gy/5 stayed acceptable to 8 or 9 of 9 wherever listed. For weight-bearing or periarticular targets, that favors moderate 5-fraction schedules over single fraction.
For a nonsurgical nonspine bone met irradiated >3 months ago, this survey supports dose de-escalation (all 9 experts after prior SBRT, 7 of 9 after prior cRT); it does not address spine targets or postoperative bone.
Site drives the objections: a majority rejected 20 Gy/1 in the humerus, acetabulum and femur cases and 50 Gy/5 in the humerus and acetabulum, while 40 Gy/5 kept 8 or 9 of 9 votes everywhere listed. For weight-bearing or periarticular NSBM, moderate 5-fraction schedules have the broadest expert backing.
14 details
Two-round survey of 9 international radiation oncologists chosen for NSBM-SBRT expertise, covering 11 cases with planning CT, MRI and GTV contours supplied. Round 2 rated each proposed schedule acceptable / not recommended / no opinion and picked 2 preferred schedules; majority defined as ≥5 of 9. Completion was 100%.
Nonsurgical nonspine bone metastases across long bones, pelvis and thorax, with RCC, breast, NSCLC and prostate primaries; some cases carried an extraosseous component.
6 experts prescribed one dose volume, 3 used an SIB with GTV/CTV or nested CTV1/CTV2 volumes. Schedules spanned 18-24 Gy/1 to 42-50 Gy/10, all at BED ≤100 Gy10.
35 Gy/5 was chosen most (29 of 99 responses), and 40 Gy/5 was the most widely accepted. Scapula was the only case where every schedule had majority acceptance. Humerus, acetabulum and femur were the only cases where a majority rejected one or more schedules.
| Schedule | BED (Gy10) | Use |
|---|---|---|
| 35 Gy/5 | 60 | Most common: 29 of 99 responses (29%); 5 experts in ≥1 case |
| 20 Gy/1 | 60 | ≥3 experts |
| 30 Gy/3 | 60 | ≥3 experts |
| 30 Gy/5 | 48 | ≥3 experts |
| Case | Not recommended by majority |
|---|---|
| Humerus (RCC) | 20 Gy/1 · 50 Gy/5 |
| Acetabulum (breast) | 20 Gy/1 · 50 Gy/5 · 8 Gy/1 + 18 Gy/1 SIB |
| Femur (NSCLC) | 20 Gy/1 |
The ≤100 Gy10 ceiling sits below the BED >100 Gy10 recommended for lung and liver SBRT. The cited Erler series reported LC 95% and 87% at 6 and 24 mo after 30-35 Gy/5, with 8.5% fracture at a median 2.5 mo; a second series of 85 NSBM reported 1-yr LC 92%.
BED equivalence assumes α/β 10 across histologies, which the authors concede may not hold for breast and prostate. Health-system and resource differences across the panel may drive part of the variation attributed to judgment.
The heterogeneity is real but bounded: a moderate-BED, 5-fraction working range emerges, and caution concentrates on weight-bearing long bones and joints. The optimal dose balancing LC and fracture stays unknown, and the authors call for phase I dose-finding and comparative trials.
Expert practice survey (n=9) with acceptability ratings; no formal consensus process and no clinical outcomes, so it maps opinion rather than testing efficacy.
- Upper dose threshold balancing LC and fracture in NSBM-SBRT
- Predictors of fracture after nonspine bone SBRT
- Toxicity profile of salvage NSBM-SBRT reirradiation
📚 Sources · 📄 1 paper
The longer read
The useful output of this survey is not the heterogeneity it headlines but the boundaries around it. Nine experienced NSBM-SBRT practitioners prescribed dozens of different schedules, yet none exceeded BED 100 Gy10, five-fraction regimens dominated, and 40 Gy/5 drew acceptance from all or all but one expert in every case where it appeared. Read that way, the paper describes a de facto working range for nonspine bone SBRT at a time when prospective dose data for these sites are close to absent.
The ceiling is the most interesting finding. Lung and liver SBRT practice anchors on BED above 100 Gy10, and this panel deliberately stayed under it. The authors attribute the restraint to fracture caution, and the site-level rejections support that reading: single-fraction 20 Gy/1 lost majority support in the humerus, acetabulum and femur cases, and 50 Gy/5 in the humerus and acetabulum. The panel is effectively treating weight-bearing long bones and periarticular targets as their own toxicity class. Whether that caution is warranted cannot be settled from the fracture data available. The cited series reported 8.5% fracture after 30-35 Gy/5, but most of those events were in ribs and iliac bones, not the long bones that worried the panel.
Whether the lower dose costs local control is the open question. The retrospective data the authors cite, LC 95% and 87% at 6 and 24 months in the Erler series and 1-year LC 92% in a second series of 85 lesions, suggest the moderate range performs acceptably. Both are retrospective, histologically mixed, and short relative to the survival horizon of an oligometastatic pt. If control erodes beyond two years in radioresistant histologies, the minority who escalated for radioresistant disease may turn out to be right, and a uniform ceiling would be the wrong lesson.
Confidence should be calibrated to the method. This is nine selected experts rating contoured scenarios, with no Delphi iteration, no outcomes, and a panel spread across health systems with different resources. The α/β 10 convention is a simplification the authors acknowledge for the breast and prostate cases, so schedules that share BED 60 Gy10 are only approximately equivalent across histologies. The unanimous de-escalation after prior SBRT is a reasonable instinct, but the authors themselves note the risk profile of salvage NSBM-SBRT is not well characterized.
What it changes: for a nonsurgical nonspine target, 35 Gy/5 and 40 Gy/5 are defensible defaults with broad expert backing, and single fraction in a weight-bearing long bone or acetabulum now carries a documented majority objection. What it does not do is define an optimal dose or show that the site-specific caution prevents fractures. Those require the dose-finding and comparative trials the authors call for.