Comparative study of experienced vs non-experienced radiologists in assessing parametric CT images of the response of the prostate gland to radiotherapy

Functional CT can demonstrate acute quantitative increases in perfusion, permeability and fractional vascular volume in the prostate gland of patients with prostate cancer following radiotherapy (RT). We hypothesize that these quantitative changes can also be demonstrated visually by presenting them as colour parametric maps using custom software. 21 patients with prostate cancer were studied before, and 1-2 weeks after, RT. Repeated CT scans through a single section of the prostate was performed following contrast injection. Capillary permeability, fractional vascular volume and tissue perfusion were calculated and converted to colour maps using a customized Matlab (R) imaging programme. Five "expert" and five "novice" radiologists scored pairs of randomized prostate images as an "increase", "decrease" or "no change" in intensity following RT. Kappa (K) statistics was used to assess the concordance of opinions. Significant quantitative increases in all indices occurred after RT, and almost all of the parametric images were scored as an increase in intensity following RT (perfusion=95%, permeability=88%, volume=84%). There was substantial agreement between the experts and novices (kappa: perfusion=0.93, permeability=0.80, volume=0.90), as well as within the expert (kappa: perfusion=1, permeability=0.86, volume=1) and novice (kappa: perfusion=0.82, permeability=0.78, volume=0.78) groups. Functional colour maps of the prostate can reliably portray the hyperaemic response following RT in a group with quantitative increases in perfusion permeability and fractional vascular volume, and provides a potentially accessible and convenient method for image analysis by radiologists of varying experience.