Adjuvant volumetric modulated arc therapy compared to 3D conformal radiation therapy for newly diagnosed soft tissue sarcoma of the extremities: outcome and toxicity evaluation

Objective: To assess the impact of adjuvant volumetric modulated arc therapy (VMAT) compared with three-dimensional conformal radiation therapy (3DCRT) in terms of toxicity and local control (LC) in patients with soft tissue sarcoma of the extremities. Methods: From 2004 to 2016, 109 patients were treated, initially using 3DCRT and subsequently with VMAT. Clinical outcome was evaluated by contrast-enhanced MRI, thoracic and abdominal CT 3 months after treatments and then every 6 months. Toxicity was evaluated with Common Terminology Criteria for Adverse Events scale v. 4.3. Results: Patients presented Stage III soft tissue sarcoma disease (77%), localized tumor (95%) at the lower extremity (87%), adipocytic histotype (46%). Surgical resection was performed in all patients, followed by adjuvant 3DCRT in 38, and VMAT in 71. The median total dose was 66Gy/33 fractions (range 60-70Gy;25-35 fractions). More successful bone sparing was recorded using VMAT (p < 0.001). Median follow-up was 61 months, 93 and 58 months for 3DCRT and VMAT group, respectively. The 2- and 5year LC were 95.3 +/- 2.1%, and 87.4 +/- 3.4% for the whole cohort, 92.0 +/- 4.5%, 82.9 16.4% for 3DCRT, 97.1 +/- 2.0%, 89.6 +/- 4.1% for VMAT (p = 0.150). On univariate and multivariate analysis the factors recorded as conditioning LC were the status of the surgical resection margins (p = 0.028) and the total dose delivered (p = 0.013). Conclusion: The availability of modern radiotherapy technique permit a better conformity on the target with maximum sparing of normal tissue and acceptable side-effects. VMAT is a safe and feasible treatment with limited rate of toxicity, compared to 3DCRT. Results on LC of VMAT are encouraging. Advances in knowledge: Soft tissue sarcoma of the extremities can benefit from the use of VMAT, with a reduction of the high dose to bones to avoid radiation osteonecrosis. An adequate total dose of at least 66Gy and a radical surgical margin allow a good local control.