Management of tumor volume changes during preoperative radiotherapy for extremity soft tissue sarcoma: a new strategy of adaptive radiotherapy

Abstract

Purpose: Using adaptive radiotherapy (ART), determine objective clinical criteria that identify extremity soft tissue sarcoma (ESTS) patients requiring adaptation of their preoperative radiotherapy (RT) plan.

Methods: We collected clinical, tumor parameter and treatment data from 17 patients with a lower extremity ESTS treated with RT, using helicoidal intensity-modulated RT (IMRT) tomotherapy, before surgical resection, between 2019 and 2021. Repositioning was ascertained by daily MV-CT (megavoltage computed tomography) imaging. Using the PreciseART technology we retrospectively manually delineated at least one MV-CT for each patient per week and recorded volume and dosimetric parameters. A greater than 5% change between target volume and planned target volume (PTV) dosimetric coverage from the initial planning CT scan to at least one MV-CT was defined as clinically significant.

Results: All 17 patients experienced significant tumor volume changes during treatment; 7 tumors grew (41%) and 10 shrank (59%). Three patients (18%), all undifferentiated pleomorphic sarcomas with increased volume changes, experienced significant reductions in tumor dose coverage. Seven patients required a plan adaptation, as determined by practical criteria applied in our departmental practice. Among these patients, only one ultimately experienced a significant change in PTV coverage. None of the patients with decreased tumor volumes had reduced target volume coverage. Monitoring volume variations by estimating GTV (gross tumor volume) on MV-CT, in addition to axial and sagittal linear tumor dimensions, appeared to be most effective for detecting reductions in PTV coverage throughout treatment.

Conclusions: Variations in ESTS volume are evident during preoperative RT, but significant dosimetric variations are rare. Specific attention should be paid to grade 2-3 UPSs during the first 2 weeks of treatment. In the absence of dedicated software in routine clinical practice, monitoring of tumor volume changes by estimating GTV may represent a useful strategy for identifying patients whose treatment needs to be replanned.