Development and application of dynamic MR-imaging for evaluation of perfusion changes in rectal carcinoma during a course of radiotherapy in clinicaluse: Preliminary results

Purpose: This study was aimed at measuring microcirculatory parameters and contrast medium accumulation within the rectal carcinoma during fractionate d radiotherapy in the clinical setting. Material and Methods: Perfusion data were observed in patients with rectal carcinoma (n = 8) who underwent a preoperative combined chemo/radiotherapy. To acquire perfusion data, an ultrafast T1 mapping sequence was carried ou t on a 1.5-Tesla whole body imager to obtain T1 maps at intervals of 14 or 120 seconds. The overall measurement time was 40 minutes. The transaxial sl ice thickness (5 mm) was chosen in such a way that both arterial vessels an d the tumor could be clearly identified. The gadolinium-DTPA (Gd-DTPA) conc entration time curve was evaluated for arterial blood and tumor after intra venous constant rate infusion. The method allows a spatial resolution of 2 x 2 x 5 mm and a temporal resolution of 14 seconds. Patients underwent MR i maging before and at constant intervals during fractionated radiotherapy. Results: Spatial and temporal resolution of dynamic T1 mapping was sufficie nt to reveal varying CM accumulation levels within the tumor and to identif y the great arteries in the pelvis. In 6 patients Gd-DTPA concentration-tim e-curves were evaluated within the tumor during radiation. Pi index of Gd D TPA versus radiation dose showed a significant increase in the first or sec ond week of treatment, then either returned slowly to pretreatment level or a renewed increase was observed. The average Pi-value at the beginning was 0.16 (+/- 0.049), reaching highest level of 0.23 (+/-0.058). In all groups the rise from the Pi-value to the Pi-maximum was statistically significant . The relative increase in perfusion ranged between 20 to 83%. Conclusion: The results show, that the ultrafast MR-technique described abo ve provide a suitable tool for monitoring tumor microcirculation during the rapeutic interventions and offers the potential for an individualized optim ization of therapeutic procedures.