PET/CT in brachytherapy early response evaluation of pancreatic ductal adenocarcinoma xenografts: comparison with apparent diffusion coefficient from diffusion-weighted MR imaging.

OBJECTIVE: To evaluate the feasibility of using PET/CT and diffusion-weighted magnetic resonance imaging (DW-MRI) to monitor the early response of pancreatic ductal adenocarcinoma (PDAC) xenografts to brachytherapy, and to determine whether maximum standardized uptake value (SUVmax) correlate with apparent diffusion coefficient (ADC).

MATERIALS AND METHODS: SW1990 human PDAC were subcutaneously implanted in 20 nude mice. They were randomly divided into 125-Iodine (125 I) seeds and blank seeds group. PET/CT and DW-MRI were performed at pretreatment and 5 days after therapy. SUVmax and ADC values were calculated, respectively. The correlation between SUVmax and ADC values was analyzed by the Pearson correlation test.

RESULTS: The SUVmax were significantly decreased between pretreatment and 5 days after 125 I seeds treatment (p < 0.001) and between two groups (p < 0.001). And the ADC values were significantly increased between pretreatment and 5 days after 125 I seeds treatment (p < 0.001) and between two groups (p < 0.001). While in the bank seeds group, there were no significantly difference between pretreatment and after treatment in SUVmax and ADC values (p = 0.057; p = 0.397). SUVmax and ADC correlated significantly and negatively before treatment in both groups (r = - 0.964, R2  = 0.929, p < 0.001; r = - 0.917, R2  = 0.841, p < 0.001) and after treatment in the blank seeds group (r = - 0.944, R2  = 0.891, p < 0.001). But after 125 I seeds treatment there was no significant correlation between SUVmax and ADC (r = - 0.388, R2  = 0.151, p = 0.268).

CONCLUSION: The PET/CT and DW-MRI are capable of monitoring the early response of PDAC xenografts to brachytherapy. The significantly inverse correlation between pretreatment SUVmax and ADC suggests that PET/CT and DW-MRI might play complementary roles for therapy assessment.