Multiple Fractionated and Single-Dose Irradiation of Bone Marrow

Purpose: To evaluate the MR appearance of bone marrow during and after multiple fractionated and single-dose irradiation using SE sequences, with histopathological correlation. Material and Methods: the left hind limbs of Wistar rats were irradiated with doses of either 2 GyX10 fractions or 20 Gy as a single dose. MR images of the femora were taken on days 0, 1, 3, 5, 7, 10, 15, 20, 25, 30, 40, 50, 60, 90, 120, 150 and 180. T1-, proton-density- and T2-weighted images were obtained with SE sequences. the rats were sacrificed on days 3, 12, 40 and 180 for histological study. Results: No significant change in the T1 relaxation time was observed in the fractionated group during the first 15 days after irradiation. T2 did not change during the initial 7 days. There were significant differences in T1 and T2 between nonirradiated and fractionated, and between fractionated and single-dose irradiated marrows ( p<0.01). Sinusoidal dilatation, decrease in cellularity, and hemorrhage were observed on day 3. Fat increased on/after day 12. the fractionated group showed mild changes compared to the single-dose irradiated group. Conclusion: the T1 and T2 relaxation times of bone marrow receiving multiple fractionated irradiation did not change significantly on SE sequences during the early phase. However, dilatation of sinusoids, hemorrhage, decrease in cellularity, and increase in fat content were observed. Single-dose irradiation resulted in marked and early changes in T1 and T2 of the bone marrow.