Functional CT imaging of the acute hyperemic response to radiation therapy of the prostate gland: early experience.

PURPOSE: Functional CT can measure perfusion and permeability. We hypothesized that acute changes could be measured in these indexes following radiation 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 repeatedly scanned after contrast medium bolus injection. Contrast agent clearance per unit volume (alpha/V) and fractional vascular volume (fvv) were calculated using Patlak graphical analysis. Perfusion was calculated as the ratio between maximal rate of tissue enhancement and peak arterial enhancement. RESULTS: Significant increases in all indexes occurred after RT. Mean perfusion rose from 0.122 to 0.263 ml/min/ml at 1-2 weeks, mean alpha/V increased from 0.0012 to 0.0016 ml/min/ml at 1-2 weeks, and mean fvv increased from 13.7 to 21% at 1-2 weeks. All three indexes remained elevated at 6-12 weeks after the start of RT. CONCLUSION: Functional CT demonstrated an acute hyperemic response following RT to the prostate gland.

Imaging of tumour therapy responses by dynamic CT.

The objective of this study was to investigate whether functional CT with Patlak analysis could be used to demonstrate acute changes associated with radiotherapy. Patlak analysis yields fractional vascular volume and contrast clearance per unit volume (a measure of permeability). Four tumour types (prostate, bronchus, breast and cervix) were studied pre-radiotherapy and at 1-2 weeks and 6-12 weeks post-therapy. Significant rises in fractional vascular volume and contrast clearance were shown at 1-2 weeks. These indices were still significantly elevated at 6-12 weeks post-therapy. In the prostates perfusion values were also elevated reflecting a hyperemic response to radiotherapy. Dynamic CT with Patlak analysis can be used to measure important pathophysiological indices which may prove useful in assessing response to therapy of tumours.