Lung Stereotactic Radiation Therapy: Intercomparison of Several Irradiation Devices in Terms of Outcome and Predictive Factors

Abstract

Background: Stereotactic body radiotherapy (SBRT) is recommended for the treatment of inoperable early stage non-small-cell lung cancer and lung oligometastases. The radiation oncology department of the Lausanne University Hospital (CHUV) gathers three different radiotherapy devices able to treat pulmonary lesions in SBRT conditions: CyberKnife® (CK), Helical Tomotherapy® (HT), and volumetric modulated arc therapy (VMAT). The aim of this study is to define the patients’ outcome in terms of irradiation efficacy and toxicities after lung SBRT depending of the choice of the SBRT technique.Methods: We retrospectively analyzed the clinical, radiological, and dosimetric data of patients with primary lung tumor or pulmonary oligometastases treated with SBRT between January 2016 and February 2020. We analyzed descriptive data using the Chi-2 test for proportions and the T-test for means comparisons, survival data by the Kaplan-Meier method and comparisons between groups by the Log-rank test and Cox-regression.Results: We identified 111 patients mostly in good condition (82.9% PS 0-1) with a median age of 71.4 years. One hundred forty-two lesions were treated with a typical fractionation of 55 Gy in 5 fractions, delivered by CK (59.9%), VMAT (38.0%), or HT (2.1%). Compared to other techniques, CK technique allowed to treat comparable gross tumor volume (GTV; 2.1 vs 1.4cc, p = 0.84) with smaller planning treatment volume (PTV; 12.3 vs 21.9 cc, p = 0.013), and was associated with a lower mean lung dose (MLD; 2.6 vs 4.1 Gy, p < 0.001), a lower V5 (13.5 vs 19.9 cc, p = 0.002) and a lower V20 (2.3 vs 5.4 cc, p < 0.001). Local control rates at 2 years were not different depending on the irradiation device, respectively of 96.2% (range, 90.8-100) and 98.1% (range, 94.4-100), p = 0.68. Toxicity incidence was significantly increased with V5 value > 17.2% (56.0 vs 77.4%, p = 0.021). Conclusions: Compared to other SBRT techniques, CK treatments permitted to treat comparable GTV with reduced PTV, MLD, V20, and V5. The dosimetric benefit of CK SBRT was not associated with a clear clinical benefit, with comparable outcome in terms of control rates and toxicity. Toxicity incidence was less frequent when reducing the V5. The use of CK is particularly attractive in case of multiple courses of lung SBRT or in case of local relapse requiring lung re-irradiation.Trial registration: Registered on February 24th 2021, ID 2021-00267, with the authorization of the CER-VD ethics committee (Switzerland).