Postradiotherapeutic changes and their evolution in MRI in children with aggressive soft tissue tumors.

Background: Magnetic resonance imaging is a commonly used method of monitoring of soft tissue tumours. The aim of the work was to describe precisely the typical changes within soft tissues and bones occurring after radiotherapy in children treated for sarcomas and other soft tissue tumours. With time, the changes undergo evolution and their characteristics and comparison with previous examinations help in a difficult differentiation between tumour lesions and posttherapeutic changes.

Material/methods: Fifteen children and young adolescents (9 boys and 6 girls) aged between 2 and 22 years (mean age of 13.4 years) with diagnosed aggressive soft tissue tumours, were treated with radiotherapy. There were 102 MRI examinations analysed in the period from February 2004 to February 2008. The examinations were performed with a 1.5T MRI scanner in the following sequences: SE T1, SE T1+fatsat, before and after gadolinium administration (Gd), FSE T2 and STIR in three planes, and, in some selected cases, a dynamic gadolinium-enhanced (DCE MRI) examination with FAME sequence. HISTOPATHOLOGICAL EXAMINATIONS SHOWED: rhabdomyosarcoma (RMS) in 8 cases, synovial sarcoma - 3, agressive desmoid fibroma - 3, mesenchymoma mal. - 1. MRI examinations were performed at different postradiotherapeutic stages, several times in one patient (12 times at the most).

Results: Every postirradiation stage revealed a typical picture of posttherapeutic changes. We distinguished four stages and described changes in different sequences within soft tissues and bones, as well as features of contrast enhancement and enhancement curves in a dynamic study. The stages included: I stage - early, up to 3 months after rth, II stage - chronic, from 3 months to 12 months after rth, with some differences between the following periods: • 3-9 months; 9-12 months; III stage - late, from 1 to 3 years after rth, IV stage - distant, more than 3 years after rth. In the early stage, there were 2 cases with a suspicious, equivocal image of postradiotherapeutic changes. In the chronic stage, there was one recurrence and one case of increasing changes after the therapy. However, the changes resolved in subsequent examinations. In the distant stage, we found two cases of a local recurrence.

Conclusions: 1. MRI is a method of choice in the monitoring of treatment of aggressive soft tissue tumours and in diagnosis of recurrence. 2. To interpret the examination results, it is very important to know the MRI characteristics of changes after radiotherapy and their evolution with time. 3. Interpretation of MRI images and differentiation between postradiotherapeutic and neoplastic changes is difficult, especially at an early postradiotherapeutic stage. 4. A dynamic MRI examination may be useful in the differentiation between postradiotherapeutic and neoplastic changes but it may be unreliable at an early postradiotherapeutic stage. 5. When interpreting the results, it is very important to compare the image with the previous ones. It is therefore indicated to carry out a baseline MRI in the early postradiotherapeutic stage, and then further follow-up images, at several-month intervals.