Assessment of radiation mediated gene therapy via multimodality imaging

Imaging techniques are under development which are intended to facilitate early analysis of spatial patterns of tumor response to combined radiation and antivascular gene therapy. We present initial results demonstrating treatment related changes of vascular permeability and blood volume maps using MRI, and tissue oxygenation measurements using electron paramagnetic resonance imaging (EPRI). Using a modified Kety model, the volume fraction accessible to the contrast agent was significantly greater in the tumor (0.81±0.11), compared to muscle (0.20±0.00, p<0.05). However, the two compartment model is probably not able to account for accumulation of contrast agent in the tumor. A three compartment model may improve fitting.