[Radiotherapy for soft tissue sarcomas of extremities. Preliminary comparative dosimetric study of 3D conformal radiotherapy versus helical tomotherapy]

Abstract

Purpose: To evaluate dosimetry of helicoidal tomotherapy versus three-dimensional conformal radiotherapy (3D-CRT) with and without IMRT for the treatment of soft tissue sarcoma (STS) of the thigh.

Methods and patients: A retrospective study was performed for three patients who received 3D-CRT as adjuvant radiation therapy for STS of the thigh. These three patients had a tumor in posterior, adductor or anterior compartment of the thigh. In each case, three treatments plans were optimised in tomotherapy, without bloc, with directional bloc and complete bloc of controlateral limb, to adequately treat the planning target volume and spare organ at risk. For each patient, we compare the three modalities of tomotherapy or "classical" IMRT from a clinac with the 3D-CRT actually performed for the treatment.

Results: Tomotherapy provides improved PTV coverage and dose homogeneity. This benefit was comparable in the three tomotherapy plans. The average D95% for tomotherapy and 3D-CRT were 97.6% and 94.8% respectively and the standard deviation is, at least, divided by two with conformal and is always better than performed with a clinac. The volume of the surrounding soft tissues receiving at least full prescription and hot spots, as evaluated by D2%, were significantly reduced in tomotherapy. Nevertheless, the results concerning the skin, the femur and the gonads were dependent on the tumor site in the thigh and not always improved with tomotherapy dosimetric studies.

Conclusions: For this preliminary study, tomotherapy can provide better coverage and dose uniformity in PTV and minimize the volume of surrounding muscular tissues receiving high doses. However, in this study, there is no benefit for others OAR (skin, femur and gonads) except in particular constraint (for instance for a precise sparing of cutaneous or bony area). Other dosimetric studies, followed by prospective evaluations with long-term follow-up are needed to determine whether tomotherapy can improve outcome for patients with STS of the thigh.