Sci-Thurs AM: YIS-08: Temporal and Dose Dependence of T2 and ADC at 9.4T in a Mouse Model Following External Beam Radiation Therapy

Abstract

A 9.4T MRI system was used to serially monitor the apparent diffusion coefficient (ADC) and transverse relaxation time (T2) of human glioblastoma multiforme (GBM) tumours grown in mice. The temporal and dose dependence of these parameters was studied in groups of mice ( per group) that were treated with a single fraction of 200 kVp x-rays of varying dose (50, 200, 400, or 800 cGy). An untreated control group was also observed using the same MRI scheme. To further examine the sensitivity of these parameters, an additional group of six mice were treated with two fractions of 400 cGy separated by 72 hours and monitored by MRI before, between, and after the two fractions. A relative increase in ADC was observed in all treated groups after irradiation. The relative increase in ADC was positively correlated with treatment dose. At two weeks post-treatment, the ADC did not return to baseline, but showed further increase. Relative T2 change was less than the relative ADC change for all treatment groups, and a significant response was not observed at all doses. T2 increased in the 800 cGy group two days after treatment, but had fallen below the pretreatment value two weeks after treatment. The response of the 2×400 cGy group agrees with the ADC and T2 response of the 1×400 cGy group during the interfraction period, and is consistent with the 1×800 cGy response after the second fraction, though lagging temporally by approximately the time between fractions.