Pre-operative radiotherapy in soft tissue tumors - Assessment of response by static post-contrast MR imaging compared to histopathology

Purpose: To evaluate if static post-contrast MR imaging was adequate to ass ess tumor viability after pre-operative radiotherapy in soft tissue sarcoma . Material and Methods: Post-contrast MR imaging of 36 soft tissue sarcomas p erformed 0-54 days (median 13 days) after pre-operative radiotherapy, were retrospectively reviewed and compared to post-operative histopathology repo rts. The contrast enhancement of the tumor was visually graded as minor, mo derate or extensive. From the post-operative histopathology reports, three types of tumor response to radiotherapy were defined: Poor, intermediate or good. The size of the tumors before and after radiation was compared. Results: Even if most viable tumors enhanced more than non-viable tumors, t here was major overlapping and significant contrast enhancement could be se en in tumors where histopathological examination revealed no viable tumor t issue. Based on histopathology, there were 12 good responders; 8 of these s howed minor, 3 moderate and 1 extensive contrast enhancement on MR imaging. Sixteen tumors had an intermediate response; 3 showed minor, 8 moderate an d 5 extensive enhancement. Eight tumors had poor response: none showed mino r enhancement, 3 moderate and 5 extensive enhancement. Both increase and de crease in tumor size was seen in lesions with a good therapy response. Conclusion: Static post-contrast MR imaging cannot reliably assess tumor vi ability after pre-operative radiotherapy in soft tissue sarcoma. In tumors with no viable tumor tissue, moderate and extensive contrast enhancement ca n be seen.