The time course of radiation therapy-induced reductions in regional perfusion: a prospective study with >5 years of follow-up.

PURPOSE: To assess the time-dependence of radiation therapy (RT)-induced reductions in regional lung perfusion, as measured by single photon emission computed tomography (SPECT) lung perfusion scans. METHODS AND MATERIALS: Between 1991 and 1999, 79 patients had SPECT lung perfusion scans before and serially after RT. Changes in regional perfusion were correlated with regional dose using 3D planning tools and image fusion (PLUNC-Plan UNC). Multiple post-RT follow-up scans were evaluated to determine the temporal nature of RT-induced regional perfusion changes. To facilitate the comparison of dose-response curves (DRCs) at different post-RT intervals, each DRC was fit to a linear model and thus described by its slope.
RESULTS: There was a dose-dependent reduction in regional perfusion at nearly all time points post-RT (p = 0.0001). The slope of the DRCs for RT-induced reductions in regional perfusion became steeper at essentially each successive follow-up interval (p = 0.0001). However, the increases in slope became progressively smaller at later follow-up intervals. Overall, about 80% of the long-term RT-induced regional perfusion injury was manifest within 12 months post-RT.
CONCLUSION: There is a progression of RT-induced reductions in regional perfusion, with most of this injury manifest within 12 months post-RT. Additional regional injury appears to evolve for years.