1991 Volume 3 Issue 4 Pages 239-249
The effect of radiation therapy on bone metastasis was studied by MR imaging. The present series included Groups I and II, Group I consisted of 32 patients with bone metastasis from lung cancer, breast cancer, renal cell carcinoma and various other malignancies that were evaluated by MR imaging before and after radiation therapy, Group II included 3 patients with preexising bone metastasis of breast cancer who were free from recurrence for more than five years after the radiation therapy. The signal intensities were standardized in 5 degrees;(I) iso-intense to normal bone marrow within the radiation field, (L) iso-intense to the muscles, (LL) hypointense to the muscles, (H) iso-intense to subctaneous fat, (HH) hyperintense to the fat.
Before radiation therapy, most bone metastasis was (L) on T1-weighted images, or (H) on T2-weighted images with enhancement by Gd-DTPA. Changes of MR images of Group I within or after 2 years had 5 variations in T1-/T2-weighted images; LL/HH (31%) as Type I, I/I (13%) as Type II, LL/LL (9%) as Type III, mixed changes as Type IV, and unchanged as NC. Gd-DTPA enhanced images before radiotherapy were mostly solid pattern in 23 of 27 patients. After radiation, the enhancement showed some decrease in 18 of these 23 patients with the following 3 patterns; mottled in 7, ring-shaped in 4 and lacking in 7. At this stage, we conclude that the decrease in enhancement was caused by radiation. Tumor size reduction on MR images was noted in 12 of 35 patients, also by radiotherapy. The 3 patients of Group II had Type III change (without enhancement).
These radiation-induced changes, in addition to past literature, reflect the pathologic features; Type I as liquefying tumor tissue, Type II as fatty change, and Type III as osteosclerosis or fibrosis. In this respect, the therapeutic effect of bone metastasis can be evaluated by the following parameters;(1) change of intensity on T1-and T2-weighted images, (2) Gd-DTPA enhancement and (3) size of tumor. Of 27 patients who showed good response to radiotherapy, 20 (74.1%) were estimated to be in the earlier stage; 5 were already in therapy and the other 15 were within 2 months after the completion of radiation therapy.
Bone metastasis has been diagnosed by X-ray films, radionuclide study and CT in the pre-MR era, however, MR imaging can be a promising diagnostic tool and a means of following up the effects of radiation therapy. Problems on precise pathologic-MR correlation should be solved in the future.
