ABSTRACT
Introduction: The COVID-19 pandemic led to worldwide barriers to access to operating rooms;some multidisciplinary thoracic oncology teams pivoted to a paradigm of stereotactic ablative radiotherapy (SABR) as a bridge to provide radical-intent treatment combining immediate SABR followed by planned surgery when surgical resource constraints ameliorated. This pragmatic approach, termed SABR-BRIDGE, was instituted with prospective data collection at four institutions (3 Canada, 1 USA);herein we present the surgical and pathological results from this approach. Methods: Eligible participants had early-stage presumed or biopsy-proven lung malignancy that would otherwise be surgically-resected. SABR was delivered using standard institutional guidelines with one of three fractionation regimens: 30-34 Gy /1 fraction, 45-55 Gy/3-5 fractions, or 60 Gy/8 fractions. Surgery was recommended at a minimum of 3 months following SABR with standardized pathologic assessment of resected tissue. A pathological complete response (pCR) was defined as absence of viable cancer, and a major pathologic response (MPR) was defined as ≤10% viable tissue. Results: Seventy-five participants were enrolled, of which 72 received SABR. Following SABR, 26 patients underwent resection, while 46 did not;reasons for not undergoing surgery included metastasis (n=2), non-cancer death (n=1), awaiting lung surgery (n=13) and patient choice given favorable post-SABR imaging response (n=30). Of 26 patients who underwent resection, 62% had a pre-treatment biopsy. The most common SABR regimens were 34 Gy /1 fraction (31%) and 48 Gy in 3-4 fractions (31%). SABR was well-tolerated, with two grade 1 toxicities (pain, 7.7%), and one grade 3 pneumonitis (3.8%). Median time-to-surgery was 4.5 months from SABR completion (range:2-17.5 months). Most had minimally-invasive surgery (n=19, 73%) with 4 patients (15%) requiring conversion to thoracotomy, and 3 (12%) had planned open operation. Surgery was reported as being more difficult because of SABR in 38% (n=10). There were two intraoperative complications (7.7%, pulmonary artery injury), and 8 patients with post-operative complications (31%, all grade 2, most commonly air leaks [n=5]). The amount of residual primary tumor ranged from 0% to 90%. Thirteen (50%) had pCR while 19 (73%) had MPR. Rates of pCR were higher in patients operated upon at earlier time points (75% if within 3 months, 50% if 3-6 months, and 33% if ≥6 months). Rates of pCR were higher in patients without pre-treatment tissue diagnosis (91% versus 20% in those without and with tissue diagnosis, respectively). In 31% (n=8) of patients, nodal disease was discovered on resection, with half being N2 (4/26=15%). Conclusions: The SABR-BRIDGE approach allowed for delivery of treatment with minimal upstaging during a period of operating room closure & high risk for patients. Surgery was well-tolerated. However, most patients who received SABR did not proceed to surgery, limiting precise estimates of pCR rates. However, the reported pCR rate is consistent with previous phase II trial data. Keywords: lung surgery, SBRT, Multi-modal therapy