Functional CT imaging of the acute hyperemic response to radiation therapyof the prostate gland: Early experience

Purpose: Functional CT can measure perfusion and permeability. We hypothesi zed that acute changes could be measured in these indexes following radiati on therapy (RT) to the prostate gland. Method: Twenty-two patients with prostatic cancer were studied before and 1 -2 and 6-12 weeks after RT. A single section through the prostate was repea tedly scanned after contrast medium bolus injection. Contrast agent clearan ce per unit volume (alpha /V) and fractional vascular volume (fvv) were cal culated using Patlak graphical analysis. Perfusion was calculated as the ra tio between maximal rate of tissue enhancement and peak arterial enhancemen t. Results: Significant increases in all indexes occurred after RT. Mean perfu sion rose from 0.122 to 0.263 ml/min/ml at 1-2 weeks, mean alpha /V increas ed from 0.0012 to 0.0016 ml/min/ml at 1-2 weeks, and mean fvv increased fro m 13.7 to 21% at 1-2 weeks. All three indexes remained elevated at 6-12 wee ks after the start of RT. Conclusion: Functional CT demonstrated an acute hyperemic response followin g RT to the prostate gland.