Intensity-modulated radiotherapy of the prostate: Dynamic ADC monitoring by DWI at 3.0 T

Background and purpose Diffusion weighted imaging (DWI) as a functional MR technique allows for both qualitative and quantitative assessment of tumour cellularity and changes during therapy. The objective of this study was to evaluate changes of apparent diffusion coefficient (ADC) in biopsy proven prostate cancer (PCa) under intensity modulated radiotherapy (IMRT) at 3T. Material & methods Thirteen patients with biopsy proven PCa treated with intensity modulated external beam radiotherapy (IMRT) underwent four standardized MR examinations after approval of the local institutional review board. These included DWI at 3T on a strict time table: before, in between, directly after (between 1 and 4days after the last radiation), as well as 3months after IMRT. Quantitative analysis of two different ADCs, - the ADC(0,800) and the ADC(50,800), was performed dynamically over 4 time points in PCa, gluteal muscle and healthy prostate tissue. Results In PCa, a significant increase of ADC(0,800)/ADC(50,800) values was measured under IMRT by about 16%/15% (P=0.00008/0.00017), 21%/21% (P=0.00006/0.00030), and 33%/34% (P=0.00004/0.00002) at the three time points compared to initial value. Healthy prostate tissue did not show any significant increase. Conclusion DWI is suitable as a biomarker for radiation therapy response of PCa by allowing the dynamic monitoring of treatment effectiveness.