Following publication of the landmark RTOG 0236, stereotactic body radiation therapy (SBRT) was rapidly implemented around the country as a curative-intent treatment for early-stage, medically inoperable non-small cell lung cancer (NSCLC) patients. Prior to the development of SBRT, such patients were treated with long (six- to seven-week) courses of conventionally fractionated radiotherapy with sub-optimal disease control and survival. SBRT has allowed these often medically frail patients to undergo a quick, convenient course of treatment over one to five fractions with excellent rates of primary tumor control—greater than or equal to 90 percent at three years in many studies.
However, the early studies treated a relatively homogeneous group of medically inoperable patients with peripherally located (i.e., more than 2 centimeters from the proximal airways) T1-2 tumors, and questions still remain as to the safety and efficacy of SBRT for challenging clinical scenarios, including centrally located tumors directly abutting critical structures, tumors touching or invading the chest wall and previously irradiated tumors. Considerable controversy also still exists as to the appropriate use of SBRT for medically operable patients and those lacking tissue confirmation. ASTRO recently published a comprehensive guideline on the clinical use of SBRT in these clinical scenarios, intended to offer pragmatic guidance to clinicians treating patients with early-stage NSCLC.
The use of SBRT among operable patients in particular continues to generate considerable controversy. Three prospective randomized trials randomizing patients between surgery and SBRT have closed prematurely secondary to poor accrual. Additional efforts to prospectively compare surgery and SBRT are ongoing through the VA (VALOR), the JoLT-Ca STABLE-MATES consortium and the RTOG Foundation. The guidelines panel unanimously and strongly endorsed these continued efforts to complete randomized prospective trials comparing surgery and SBRT.
In the absence of completed trials, the ASTRO guideline endorses surgical resection as the standard-of-care for patients fit for lobectomy, although it states that discussions about SBRT are reasonable as part of a shared decision-making process. For those patients deemed “high-operative risk” (an admittedly nebulous term as the definition varies between studies and between surgeons), discussions about SBRT are encouraged, with full disclosure that long-term data on the efficacy of SBRT beyond a three-to-five year window is limited. It was recommended that all potentially operable patients undergo consultation with a thoracic surgeon who performs lung cancer resections.
The guideline also addresses patients lacking tissue confirmation. Radiation oncologists are traditionally taught the mantra of “no meat, no treat.” However, a growing body of literature has emerged that questions this dogma for patients with radiographically convincing lung tumors who are at significant or prohibitive risk from biopsy. Such patients may face more risks from the biopsy than from the treatment of the tumor. The panel endorsed that, first, whenever possible, a biopsy should be obtained prior to treatment, and second, that SBRT can be delivered in consenting patients who have a prohibitive risk or refuse biopsy after multidisciplinary imaging review with consensus the lesion is radiographically and clinically consistent with lung cancer.
The additional key questions within the guideline largely focus on risk-benefit analyses for challenging clinical scenarios that may pose significant risk of toxicities, but for which no other curative-intent treatment is feasible. These included centrally located tumors, particularly those with unique and substantial risks, such as those abutting the esophagus, multi-focal tumors and recurrent tumors within a previously irradiated field. The consistent themes across these recommendations include appropriate patient consent, shared decision-making and multidisciplinary discussion, and guidance is provided as to optimizing dose and fractionation.
The development and refinement of SBRT has provided a potentially curative treatment to patients who previously had few treatment options. Continued high-quality clinical research should allow us to further refine fractionation schedules and dose constraints to optimize both safety and tumor control.
Dr. Daly served as co-chair of the task force that authored this guideline. She is a radiation oncologist at the University of California, Davis in Sacramento, California.