Single Fraction (30 Gy) Stereotactic Body Radiation Treatment of Peripheral Lung Lesions using Flattening Filter Free Volumetric Modulated Arc Therapy (FFF-VMAT): Early Clinical Outcomes

Abstract

To present early clinical outcomes utilizing stereotactic body radiation therapy (SBRT) to mid lung or peripheral lung lesions, delivering a dose of 30 Gy in a single fraction with flattening filter free volumetric modulated arc therapy (FFF-VMAT). Twenty-four lesions were identified from twenty-three patients with either early stage non-small cell lung cancer (lesions n = 17) or isolated, limited, thoracic progression from a known metastatic cancer diagnosis (lesions n = 2 head and neck, n = 2 rectal, n = 3 lung). Patients were prescribed a single dose of 30 Gy, delivered using FFF VMAT with noncoplanar 6MV beams and cone beam CT image guidance. Four-dimensional (4D) CT based treatment plans were generated using an advanced Acuros-based dose calculation engine for heterogeneity corrections. Plan quality and delivery efficiency were reported. Outcomes evaluated include local control, radiation-induced pneumonitis, and rib toxicity. Median follow-up time was 9 months (range: 1 to 38 months). Mean planning target volume (PTV) was 17.6 ± 13.9 cc. All plans met RTOG requirements for target coverage and dose to organs at risk (OAR). Average values of the conformity index, gradient index, maximum dose at 2 cm away from the PTV, normal lung V20Gy, and normal lung V10Gy were 1.06 ± 0.1, 5.4 ± 1.4, 49.5 ± 4.5%, 0.8 ± 0.5% and 3.2 ± 1.9 %, respectively. All OAR doses were well below RTOG compliance criteria. Average beam on time was 6.6 ± 1.3 min. Four patients were lost to follow up. One patient has initial post-treatment imaging pending. During the follow up period, all patients demonstrated local control of the treated lesion. Six patients developed new distant metastases, 4 of whom had prior stage 4 disease. All patients developed asymptomatic radiographic changes surrounding the treated lesion, though there were no reports of grade 2+ pneumonitis or chest wall pain and no radiographic evidence of rib fracture. Stereotactic delivery of 30 Gy in a single fraction using cone-beam CT image guidance with a non-coplanar FFF-VMAT plan is a fast, safe, and effective treatment modality for managing small mid-lung or peripherally located lung lesions. Local control is excellent and no symptomatic adverse events were noted over the follow up period. This is a promising strategy for rapidly delivering a meaningful oncologic dose to patients unable to tolerate a multi-fraction regimen due to discomfort, medical comorbidities, or socio-economic barriers hindering treatment compliance. Longer clinical follow up in a larger patient cohort is ongoing to further validate these outcomes.