KEY POINTS
- This exploratory study tested retroperitoneal hydrogel placement in 3 Thiel-embalmed cadavers, with 10 mL of spacer injected under CT guidance into the perirenal, perivascular, or iliacus compartments.
- Spacer behavior differed markedly by anatomy. In the perirenal compartment, approximately 1 cm of kidney–bowel separation was maintained with 87.3% volume retention at one month and minimal positional change.
- Perivascular injection performed poorly: the hydrogel lost its discrete configuration immediately and became indistinguishable on follow-up imaging. Iliacus placement remained stable but produced little clinically useful bowel displacement.
- A simulated renal cell carcinoma SBRT plan was generated in the successful perirenal case using 26 Gy in a single fraction, with PTV D99 normalized to prescription in both pre- and post-spacer plans.
- Small-bowel Dmax decreased from 25.1 to 22.7 Gy, while D2cc changed from 13.2 to 12.7 Gy. The effect was larger for large bowel: Dmax decreased from 34.5 to 22.1 Gy and D2cc from 20.8 to 15.0 Gy.
- Target coverage remained broadly comparable after spacer placement, suggesting that the dosimetric gain came primarily from physical bowel displacement rather than target compromise.
- The experiment cannot establish safety, injectability, stability, or benefit in living patients; the authors explicitly describe it as exploratory and hypothesis-generating.
CLINICAL TAKEAWAY
Perirenal hydrogel placement is anatomically plausible and could become useful when bowel proximity prevents ablative kidney SBRT. For now, however, this is preclinical evidence from a single simulated treatment scenario—not a clinically validated spacer technique.