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Aim: To assess the changes in the angiogenic status of rectal cancer before and after preoperative radiotherapy (RT) using endosonography (ES). Material and methods: Fifty-four patients with rectal cancer were examined by ES before and 6-7 weeks after preoperative RT and . The tumour size, stage, echostructure and vascularization before and after RT were compared. Tumour vascularization was determined by qualitative power Doppler and by computer-assisted method. Results: Compared to the histological data, ES restaging after RT was accurate in 65% of the cases for the T parameter and in 83% for the N parameter (TNM tumour classification). The histological data compared with the initial ES examination revealed downstaging in relation to the T parameter in 33% and for the N stage in 24% of the cases. The tumour structure following RT became hyperechogenic in 89% of tumours and remained hypoechogenic in 11% of tumours. Power Doppler found a reduction in tumour vascularization after RT in 61% of the tumours. The PDVI before RT was 10.7±5.8% and 6.3±4.6% after RT (p<0.05). A strong correlation between the qualitative assessment of the vascularization and PDVI was found (r=0.536, p<0.001). The vascularization reduction after RT was found to be a protective factor which decreased the death risk by about 86 % (OR=0.14, p=0.001). Conclusions: Endorectal Doppler sonographic findings are promising in the evaluation of tumour vascularization in patients with rectal cancer. The qualitative and quantitative digital assessment of the vascularization gives supplementary information about the patients' prognosis. [ABSTRACT FROM AUTHOR]