Value of Diffusion-Weighted MR Imaging as an Early Surrogate Parameter for the Response of Colorectal Metastases to Interstitial 192Ir-High-Dose-Rate Brachytherapy

Oliver Dudeck¹, Christian Wybranski¹, Martin Zeile¹, David Lwenthal¹, Frank Fischbach¹, Maciej Pech¹, Gero Wieners¹, Jens Ricke¹

Forty colorectal liver metastases in 30 patients were evaluated with MRI including diffusion-weighted imaging (DWI) immediately before, 2 days after and 90 days following CT- and MR-guided brachytherapy. Tumor diameter (TD) and ADC were evaluated by two radiologists. On early postprocedural MRI, mean TD sligthly incresed while mean ADC decreased significantly (p<0,001). On follow-up MRI, a decrease in mean TD correlated with an increase of mean ADC (p<0,001 both; r=-0,565). In conclusion, changes in ADC can be assessed as soon as 2 days following brachytherapy. Early ADC decrease most likely reflected cell swelling, late increase reduction of tumor cell density.