Volume changes in soft tissue sarcomas during preoperative radiotherapy of extremities evaluated using cone-beam CT

Objective The objective of this study is to quantify volume changes in the gross target volume (GTV) during preoperative radiotherapy for extremity soft tissue sarcomas (ESTS). Methods Twenty-seven patients with ESTS, treated with preoperative radiotherapy, were included in this study. Weekly cone-beam CT scans acquired for setup correction were used for GTV delineation in order to quantify volume changes over the course of treatment. Age, anatomical location, tumour type and tumour volume were evaluated as predictive factors for volume changes. Finally, the optimal time point for adaptive intervention was quantified. Results A GTV increase to a maximum of 28 % occurred in five patients. Thirteen patients showed no change and nine patients (all diagnosed with myxoid liposarcoma (MLS)) showed a GTV decrease to a maximum of 57 % of the GTV volume at start of treatment. In the multivariate analysis, only the relative volume change for tumour type was significant (p= 0.001). The optimal time point for adaptive intervention in non-MLS patients was the first week and for MLS patients the third week. Conclusions Volume changes were quantified during preoperative RT of ESTS. Volume decrease was observed only in MLS patients. Individualised treatment resulting in plan adaptations could result in a clinically useful volume reduction for MLS patients.