Effect of external beam radiotherapy on prostate ADC values

Introduction The effects of ionising radiation on cells are complex and include cell apoptosis, cell swelling and cell lysis, all of which affect the cellular density. The aim of this study was to investigate if the apparent diffusion coefficient (ADC) changed before and after external beam radiotherapy (EBRT) in response to these effects using similar acquisition techniques to studies that have demonstrated a significant difference in ADC between normal prostatic peripheral zone and prostate cancer (1,2). The effect of using different combinations of b-values to calculate the ADC was also investigated. Methods. 17 patients who were undergoing radical EBRT (55 Gy in 20 fractions) for localized prostate cancer participated in this study. All patients had been on hormone therapy prior to EBRT commencing. Patients were excluded if they had contraindications to MRI scanning. MRI scans were performed on a 1.5T Siemens Avanto scanner with SQ gradients. All patients had T2W-TSE and diffusion MRI scans of their prostate before the first EBRT fraction and immediately after their last fraction of EBRT. The diffusion MRI scans used a single-shot diffusion weighted echo-planar imaging (DWEPI) sequence using a 3-scan trace diffusion acquisition with b-values of 0, 50, 300, 500 and 800 s/mm. The slice positions of T2W-TSE and DWEPI scans were matched.