Radiosensitivity of rat mammary tumors correlates with early vessel changes assessed by power Doppler sonography.
OBJECTIVE
To investigate the changes occurring in the vascularization of tumors during irradiation, we used a model of autochthonous mammary tumors in rats and assessed early vascular changes after irradiation by power Doppler sonography.


METHODS
Mammary tumors were induced in 24 female Sprague Dawley rats by a single subcutaneous injection of N-nitroso N-methyl urea. After tumor areas reached 1 cm2, the animals received a single fraction of 18-Gy radiation or intraperitoneal saline injection. Power Doppler sonographic quantification of detected vessels was performed 1 day before irradiation and 7 days after the use of a power Doppler index of 5 different tumor imaging planes. Final tumor shrinkage was compared with early changes in the power Doppler index. Not all tumors regressed in a similar fashion. Radiosensitive tumors were defined as tumors with a greater than 50% decrease in baseline area 28 days after irradiation, whereas radioresistant tumors were tumors with a less than 50% decrease in baseline area. Statistical analysis was performed by the Mann-Whitney U test.


RESULTS
Tumor area changes were similar in radioresistant and radiosensitive tumors 7 days after irradiation (-41% and -35%, respectively; P > .05, not significant), whereas reduction in the power Doppler index was significantly greater in radiosensitive tumors (mean value, -63%) than in radioresistant tumors (mean value, -12%) (P = .001). Late tumor regrowth was correlated with day 7 power Doppler index changes (P = .009). A 40% reduction in the power Doppler index at day 7 distinguished 8 of 9 radiosensitive tumors and 8 of 9 radioresistant tumors (P = .003).


CONCLUSIONS
This study suggests that early changes in tumor perfusion as assessed by power Doppler sonography after tumor irradiation may precede the long-term tumor regression.
D000818:Animals; D005260:Female; D008325:Mammary Neoplasms, Experimental / Q000139:chemically induced / Q000000981:diagnostic imaging* / Q000532:radiotherapy; D008770:Methylnitrosourea; D023421:Models, Animal; D009389:Neovascularization, Pathologic / Q000000981:diagnostic imaging*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012965:Sodium Chloride / Q000008:administration & dosage; D018709:Statistics, Nonparametric; D018608:Ultrasonography, Doppler / Q000379:methods*
D012965:Sodium Chloride; D008770:Methylnitrosourea