KEY POINTS
- Investigators replanned 15 bulky retroperitoneal sarcomas using hypofractionated RT with a simultaneous central boost. The cohort was heavily enriched for liposarcoma, with 12/15 tumors (80%) classified as well- or dedifferentiated liposarcoma.
- The experimental three-week strategy prescribed 42.75 Gy in 15 fractions to the PTV, 45 Gy in 15 fractions to the internal GTV and 52.5 Gy in 15 fractions to a central SIB volume.
- All 15/15 plans met prespecified target-coverage criteria for the PTV, iGTV and boost. Mean PTV CI95% was 0.99, indicating highly conformal prescription coverage.
- Only 10/15 plans met every target and OAR objective. The other five exceeded at least one bowel objective, although every deviation was by less than 1% of the specified constraint.
- Bowel proximity remained the principal limitation. The largest large-bowel maximum dose was 45.4 Gy versus a 45-Gy objective, and deviations occurred specifically where bowel directly abutted tumor. The duodenal constraint was met in every plan.
- Bilateral kidney objectives were exceeded in 4 patients, although interpretation was complicated by ipsilateral renal involvement and cases in which the affected kidney was difficult to distinguish from tumor.
- These were planning simulations, not delivered treatments. The selected patients ultimately underwent surgery and should not be considered equivalent to patients with genuinely unresectable disease. The assumed sarcoma α/β of 3 Gy and biological rationale for the central boost also remain uncertain.
CLINICAL TAKEAWAY
A 15-fraction central-boost strategy can be planned even for very large retroperitoneal tumors, but bowel and kidney anatomy remain the limiting factors. The study establishes plan-generation feasibility only; whether 52.5 Gy to the tumor centre improves control or can be delivered safely is unknown.