Single-Isocenter/Multi-Lesion Synchronous Lung Stereotactic Body Radiation Therapy (SBRT): Plan Quality, Treatment Efficiency and Clinical Outcomes

Abstract

Patients with multiple primary or metastatic lung lesions may not well tolerate relatively longer SBRT treatments due to distress or shortness of breath, with traditional treatment planning and delivery with individual isocenter per lesion. Treating lesions synchronously with a single-isocenter volumetric modulated arc therapy (VMAT) plan with flattening filter free (FFF) beam will decrease treatment time and improve patient comfort. We report dosimetry, treatment efficiency and early clinical outcomes of oligometastases (< 5 lesions) lung cancer patients who underwent synchronous single-isocenter/multiple-lesions VMAT lung SBRT. Fourteen patients with multiple peripherally located non-small-cell-lung cancer (NSCLC) lesions (two n = 12, three n = 1, five n = 1, total 32 lesions) were treated synchronously with highly conformal single-isocenter non-coplanar VMAT-SBRT plan (bilateral lesions n = 6, right lesions n = 5, left lesions n = 3). Single-isocenter was placed between or in the middle of all lesions. Doses were 54 Gy/50 Gy in 3/5 fractions prescribed to 70-80% isodose line. Plans were generated with Acuros-based algorithm and 6MV-FFF beam following RTOG criteria. Plan quality and delivery efficiency were reported. Outcomes evaluated include local control rates, radiation pneumonitis and rib toxicity. Kaplan-Meier (KM) estimates of time-to-local failure were investigated. Median follow-up time was 5 ± 5 months (range 1 to 15 months). Mean isocenter to tumor distance was 5.6 ± 1.9 cm. Mean combined planning target volume (PTV) was 38.7 ± 22.7 cc. All plans were accepted by treating physicians and met RTOG criteria for target coverage and organs at risk (OAR) dose. Average values of conformity index, gradient index, maximum dose at 2 cm away from the PTV and normal lung V20 were 1.05 ± 0.1, 5.1 ± 0.8, 50.1 ± 5.2% and 6.4 ± 3.1%, respectively. All OAR doses were well below RTOG criteria. Additionally, normal lung V10, V5 and mean lung dose were 18.2%, 31.0 % and 5.4 Gy, on average, respectively. Average beam on time was 3.4 ± 1.4 min. One patient died before follow up and one was lost to follow up. Of twelve patients, eleven achieved complete response to treatment with one lesion of one patient progressing. KM estimated 1-year actuarial tumor local control rate was 100%; however, 50% of the patients developed distant metastases. During the follow-up period, no patient had adverse pulmonary effects, developed grade+2 pneumonitis or had chest wall pain/rib fracture. However, four patients developed radiographic changes that were asymptomatic. Synchronous SBRT treatment to oligometastases lung lesions was fast, effective and safe, with promising early clinical outcomes in terms of local control rates and no adverse side effects to lung or ribs. Although six patients had distant failure, the local control of treated lesions could preserve the patient’s quality of life or delay chemotherapy treatment. Longer follow up of these patients is warranted.