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

Abstract

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 66 Gy/33 fractions (range 60-70 Gy;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 5 year LC were 95.3±2.1%, and 87.4±3.4% for the whole cohort, 92.0±4.5%, 82.9±6.4% 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 66 Gy and a radical surgical margin allow a good local control.

Figure 1.

Dose distribution for a 3DCRT and a VMAT patient. 3DCRT,three-dimensional conformal radiation therapy; VMAT, volumetric modulated arctherapy.

Figure 2.

DVH of bone. On the left: tolerance DVH for G4 toxicity; on the right: DVH of the whole patient cohort, in black bold the patients who had G4 toxicity, in dotted line the tolerance DVH as plot on the left. DVH,dose–volume histogram.

Figure 3.

Kaplan–Meier plot of the local lontrol for the whole patient cohort (on the upper left), stratified by RT technique (upper right), by surgical margin (lower left), and by prescription dose (lower right). 3DCRT,three-dimensional conformal radiation therapy; RT,radiation therapy; VMAT, volumetric modulated arctherapy.

Figure 4.

Kaplan–Meier plot of the disease free survival for the whole patient cohort (on the left), and stratified by RT technique (on the right). 3DCRT,three-dimensional conformal radiation therapy; RT, radiation therapy; VMAT, volumetricmodulated arc therapy.

Figure 5.

Kaplan–Meier plot of the overall survival for the whole patient cohort (on the left), and stratified by RT technique (on the right). 3DCRT,three-dimensional conformal radiation therapy; RT, radiation therapy; VMAT, volumetricmodulated arc therapy.