Change in diffusion weighted MRI during liver cancer radiotherapy: Preliminary observations

Purpose. To evaluate diffusion weighted magnetic resonance imaging (DWI) in liver and liver cancers during and following conformal radiotherapy (RT). To determine the feasibility of using changes in apparent diffusion coefficients (ADC) as a potential surrogate for tumour control or normal tissue injury. Materials and methods. Patients on a six-fraction conformal liver RT protocol underwent DW-MRI at the time of treatment planning, during RT (week one and two) and one month following RT. Diffusion weighted MR images were acquired in exhale breath hold, using b-values of 0 and 600. Regions of interest (ROIs) corresponding to maximal tumour dose, high-dose peri-tumour liver, irradiated normal liver, non-irradiated liver, and spleen were analyzed on ADC maps. Results. Eleven patients (four hepatocellular carcinoma, five liver metastases, two cholangiocarcinoma) were evaluated. The baseline median tumour ADC of 1.56 x 10(-3) mm(2)/sec increased to 1.89 x 10(-3) mm(2)/sec at RT week one, to 1.91 x 10(-3) mm(2)/sec during week two and to 2.01 x 10(-3) mm(2)/sec at one month following treatment (p<0.0001). Early increases in mean ADC were correlated with higher dose and sustained tumour response, whereas RECIST and volume changes on T2 images were not. Peri-tumour mean ADC also increased, from 1.40 x 10(-3) mm(2)/sec (baseline) to 1.55 x 10(-3) mm(2)/sec (RT week 2) and 1.64 x 10(-3) mm(2)/sec (follow-up). Small ADC changes were seen in the irradiated liver, and no significant changes were seen in the un-irradiated liver. Conclusions. Changes in tumour ADC were seen during RT. Larger increases were correlated with higher doses and increased likelihood of response.