Radiation-induced changes in MR signal intensity and contrast enhancement of lumbosacral vertebrae: do changes occur only inside the radiation therapy field?

PURPOSE: To evaluate temporal changes in signal intensity (SI) and degree of contrast enhancement (CE) of bone marrow in lumbosacral vertebrae inside and outside the radiation therapy (RT) field.
MATERIALS AND METHODS: Twenty-three patients with advanced uterine cervical cancer who were treated with RT were prospectively evaluated. Each patient underwent four dynamic magnetic resonance (MR) studies: before RT, 2 and 4 weeks after initiation of RT, and 4 weeks after completion of RT. SI and CE were calculated in all four studies of each patient.
RESULTS: Bone marrow inside the RT field showed steady and marked increase in precontrast SI and early and transient increase in CE at 2 weeks after initiation of RT followed by progressive and marked decrease in CE at 4 weeks after initiation of RT and 4 weeks after completion of RT. Bone marrow outside the RT field showed slight increase in precontrast SI and steady and moderate decrease in CE to a lesser degree without early increase as seen in bone marrow inside the RT field.
CONCLUSION: RT causes an increase in precontrast SI predominantly in bone marrow inside the RT field. However, a decrease in CE is seen in bone marrow not only inside but also outside the RT field.