Implementation and Safety of a Single Fraction Peripheral Lung SBRT during the Global COVID-19 Pandemic, a Single Institution's Experience

PURPOSE/OBJECTIVE(S): In response to the COVID-19 pandemic, a single fraction peripheral lung SBRT program was established to minimize potential COVID-19 exposures. This analysis aims to review clinical and treatment characteristics and associated toxicities in appropriately selected patients for this newly implemented technique. MATERIALS/METHODS: From May 2020 until Feb 2022, patients with peripheral lung tumors who met eligibility for 3400cGy in a single-fraction SBRT were treated at a tertiary academic cancer center. Patient, treatment, and toxicity parameters were retrospectively collected. Radiation dosimetric parameters were tabulated. Toxicities were quantified using CTCAE v5.0. Fisher's exact test was used to assess the differences in toxicities with clinical and dosimetric parameters. P-value < 0.05 was considered significant. RESULTS: 23 patients were analyzed with a median age of 72 years (IRQ: 67-80) and 61% were females. 96% were smokers and 43% had COPD. All patients were ECOG ≤ 2. Majority of patients (96%) had early-stage primary lung cancer while 4% had pulmonary oligometastatic cancer. 39% of patients were treated on SABR-BRIDGE protocol while another 35% were medically inoperable and 26% refused surgery. A total of 23 peripheral lesions were treated with median greatest dimension of 1.7 cm (IQR: 1.4-2), ITV 4.9 cm(3) (IQR: 3.6-8.4) and PTV 18.1 cm(3) (IQR: 12.8-26). 87% had PTV within 1 cm form chest wall. After median follow-up of 6 months (IQR: 2-12), 52% of patients experienced grade ≤ 2 toxicities and no patients experienced ≥ grade 3. Radiation pneumonitis was the most common toxicity (35%; 5/8 with asymptomatic radiographic) followed by fatigue (30%) and chest wall pain (30%; 3/7 with grade 2). Two patients (9%) had rib fractures. Chest wall pain was significantly higher in patients with tumor diameter >1.5 cm (p = 0.02). No other significant difference was observed between clinical or dosimetric parameters and development of radiation pneumonitis or chest wall pain (p > 0.05). On the other hand, patients with ribs fractures were observed to have larger tumors (mean 3.2 vs. 1.7 cm), ITVs (mean 30 vs. 11 cm(3)), PTVs (mean 61 vs. 16 cm(3)), chest wall V30(Gy) (mean 4.8 vs. 0.4 cm(3)), and ribs V30(Gy) (mean 1.1 vs. 0.1 cm(3)). Only 1 patient had local failure after 12 months while another patient on SABR-BRIDGE underwent surgical resection after 6 months in which there were 20% viable tumor cells. CONCLUSION: Single fraction peripheral lung SBRT is a practical and safe option with no grade ≥ 3 toxicity. Our observed toxicities are within previously reported ranges. We observed that patients with rib fractures had larger tumors and higher V30(Gy) to chest wall and ribs. Careful patient selection and dosimetric efforts to limit high fall-off dose to chest wall and ribs may limit these toxicities.