UC Irvine

Rationale and objectives

To use a rapid gas-challenge blood oxygen-level dependent magnetic resonance imaging exam to evaluate changes in tumor hypoxia after ⁹⁰Y radioembolization (Y90) in the VX2 rabbit model.

Materials and methods

White New Zealand rabbits (n = 11) provided a Y90 group (n = 6 rabbits) and untreated control group (n = 5 rabbits). R2* maps were generated with gas-challenges (O₂/room air) at baseline, 1 week, and 2 weeks post-Y90. Laboratory toxicity was evaluated at baseline, 24 hours, 72 hours, 1 hours, and 2 weeks. Histology was used to evaluate tumor necrosis on hematoxylin and eosin and immunofluorescence imaging was used to assess microvessel density (CD31) and proliferative index (Ki67).

Results

At baseline, median tumor volumes and time to imaging were similar between groups (p = 1.000 and p = 0.4512, respectively). The median administered dose was 50.4 Gy (95% confidence interval:44.8-55.9). At week 2, mean tumor volumes were 5769.8 versus 643.7 mm³ for control versus Y90 rabbits, respectively (p = 0.0246). At two weeks, ΔR2* increased for control tumors to 12.37 ± 12.36sec^-1 and decreased to 4.48 ± 9.00sec^-1 after Y90. The Pearson correlation coefficient for ΔR2* at baseline and percent increase in tumor size by two weeks was 0.798 for the Y90 group (p = 0.002). There was no difference in mean microvessel density for control versus Y90 treated tumors (p = 0.6682). The mean proliferative index was reduced in Y90 treated tumors at 30.5% versus 47.5% for controls (p = 0.0071).

Conclusion

The baseline ΔR2* of tumors prior to Y90 may be a predictive imaging biomarker of tumor response and treatment of these tumors with Y90 may influence tumor oxygenation over time.