Sixteen New Zealand white rabbits received a subcutaneous implantation of VX2
tumor cell
suspension 0.5 mL (4 x 10(7) cells/mL) in their right thighs to set up
tumor model. And 2 weeks later they were randomly divided into therapy group (Group T, n = 10) and control group (Group C, n = 6). Group T received
radiotherapy at a single dose of 10 Gy. MR imaging (MRI) scan including short TI inversion recovery echo-planar imaging DWI, T1-weighted imaging (T1WI) and T2-weighted imaging (T2WI) sequences were performed 1 day prior to as well as 1 day, 2 days, 3 days and 7 days after
radiotherapy. Group C received only MRI scan at the same time points without any treatment. MRI appearance on T2WI, T1WI, and DWI images was compared and
tumor volume was calculated. Apparent diffusion coefficient (ADC) values of the
tumor were evaluated in all cases. HE staining was used for pathological study.
RESULTS:
Necrosis (n = 8) and
hemorrhage (n = 2) were seen gradually on T2WI and T1WI images of Group T after time point of day 2 after irradiation. In Group C, no obvious
necrosis was found until day 7. There was no significant difference in
tumor volume between the two groups before
radiotherapy. After
radiotherapy,
tumors in Group T showed a gradual growth but not as obvious as Group C. There was a significant difference in
tumor volume between the two groups from day 2 on (P < 0.05). ADC value changed dramatically right from the 1st day after
radiotherapy in Group T [(0.99 +/- 0.15) x 10(-3) mm2/s for 1 day before
radiotherapy, (1.23 +/- 0.08) x 10(-3), (1.45 +/- 0.07) x 10(-3), (1.63 +/- 0.06) x 10(-3), and (2.02 +/- 0.18) x 10(-3) mm2/s for day 1, 2, 3, and 7]; and ADC value had no significant changes after
radiotherapy in Group C except day 7 [(1.07 +/- 0.08) x 10(-3) mm2/s for 1 day before
radiotherapy, (1.03 +/- 0.04) x 10(-3), (1.05 +/- 0.02) x 10(-3), (1.05 +/- 0.05) x 10(-3), and (0.95 +/- 0.07) x 10(-3) mm2/s for day 1, 2, 3, and 7]. There was significant difference in ADC value between the two groups for each time point after
radiotherapy (P < 0.01). Pathological study showed that the number of viable
tumor cells in Group T decreased 1 day after
radiotherapy, and the inflammatory cell infiltration was marked and almost all viable
tumor cells disappeared by day 7 after
radiotherapy.
CONCLUSIONS: DWI is a new promising technique for monitoring
radiotherapy outcomes. ADC value may give a prior clue on physiological changes of
radiotherapy before routine MRI could tell.