An ASCO Expert Panel has endorsed an American Society for Radiation Oncology (ASTRO) guideline on radiation therapy for small cell lung cancer (SCLC), stating the recommendations in the ASTRO guideline “are clear, thorough, and based upon the most relevant scientific evidence” available.1
Radiotherapy in SCLC: Current Directions and Unanswered Questions
The ASCO endorsement was co-chaired by Megan E. Daly, MD, of the University of California Davis Health, and Bryan J. Schneider, MD, of the University of Michigan School of Medicine.
Megan E. Daly, MD
Bryan J. Schneider, MD
“The ASTRO guideline addresses the use of radiotherapy for both limited- and extensive-stage SCLC,” Dr. Daly told ASCO Daily News. “There are several specific scenarios within this guideline that have not been comprehensively addressed previously.”
Within the ASCO endorsement, the Expert Panel noted that there currently exist certain areas of controversy surrounding the use of radiotherapy for SCLC, including:
- Optimal dose and fractionation for limited-stage SCLC;
- Appropriateness of prophylactic cranial irradiation in limited- and extensive-stage SCLC; and
- Role of consolidative thoracic radiotherapy for extensive-stage disease.
Additionally, the Expert Panel indicated that there is a general lack of consensus regarding patient selection and radiation technique, such as conventional radiotherapy vs stereotactic body radiotherapy (SBRT). The ASTRO guideline represents a critical piece of the puzzle that seeks to address gaps in standardized radiotherapy recommendations.
Below is a brief summary of the endorsed ASTRO recommendations and clarifications from ASCO.
Thoracic Radiotherapy for Limited-Stage SCLC
In ITS guideline, ASTRO made a strong recommendation for thoracic radiotherapy for patients with limited-stage SCLC who can tolerate definitive therapy. In similar patients who are receiving chemotherapy, the guideline recommends thoracic radiotherapy beginning at cycle 1 or 2 of chemotherapy. The Expert Panel clarified that thoracic radiotherapy in patients receiving chemotherapy should include twice-daily hyperfractionated regimens.
Role of SBRT in Stage I/II Node-Negative SCLC
ASCO suggests that the use of SBRT is increasing in patients with SCLC who are not eligible for resection or who decide to opt out of undergoing surgery. Additionally, retrospective data suggest this strategy is likely safe and effective. The ASTRO guideline incorporates SBRT as an acceptable treatment option for early-stage, node-negative, and medically inoperable SCLC, a recommendation that has not been addressed in previous guidelines, Dr. Daly said.
“The ASTRO guideline addresses the use of radiotherapy for both limited- and extensive-stage SCLC. There are several specific scenarios within this guideline that have not been comprehensively addressed previously.”— Megan E. Daly, MD
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In an implementation remark, the guideline suggests conventional fractionation schema may be more appropriate for ultracentral tumors, which ASCO clarified as tumors “with the planning target volume touching or overlapping the proximal bronchial tree, esophagus, or trachea.” The ASCO Expert Panel adds that patients considered for SBRT for early-stage disease should also undergo extensive assessment for nodal or distant metastatic cancer.
Prophylactic Cranial Irradiation
The new ASTRO guideline addresses the use of prophylactic cranial irradiation, which represents an area of controversy following the publication of a Japanese randomized phase III trial that found magnetic resonance imaging (MRI) surveillance could replace prophylactic cranial irradiation for extensive-stage disease.
“There has been significant discussion and debate over the ongoing role of [prophylactic cranial irradiation],” Dr. Daly said. “The ASTRO guideline continues to recommend [prophylactic cranial irradiation] for patients with limited-stage disease and recommends a shared decision-making approach for extensive-stage disease.”
The ASCO Expert Panel agrees with ASTRO on a shared decision-making approach involving prophylactic cranial irradiation for extensive-stage SCLC. The use of prophylactic cranial irradiation should remain standard of care in limited-stage SCLC, however, at least until additional data can show that MRI surveillance does not compromise overall survival when used in lieu of prophylactic cranial irradiation.
Dr. Daly added that “the role of [prophylactic cranial irradiation] in limited-stage SCLC also remains in question,” as does whether MRI surveillance can be used in these patients. She said that this topic is currently under investigation in the MAVERICK trial (ClinicalTrials.gov identifier NCT04155034).
Thoracic Consolidation for Extensive-Stage SCLC
Finally, the ASTRO guideline encourages consideration of consolidative thoracic radiation for extensive-stage SCLC where immunotherapy is incorporated into front-line treatment. Dr. Daly noted, however, that no prospective trials have been completed to address this topic.
“Better data are needed to determine if consolidative thoracic radiation remains beneficial when immunotherapy is incorporated in the front-line setting,” she said. Dr. Daly added that the currently accruing RAPTOR trial (NCT04402788) is seeking to address this question.
The ASTRO guideline conditionally recommends thoracic radiotherapy to 3,000 cGy in 10 fractions within 6 to 8 weeks in patients with extensive-stage SCLC with a response to chemotherapy and immunotherapy as well as residual disease in the thorax. ASCO clarifies this statement by noting this dose should be initiated in these patients within 6 to 8 weeks of chemotherapy completion and prior to maintenance immunotherapy.
REFERENCE
1. Daly M, Ismaila N, Decker RH: Radiation therapy for small cell lung cancer: ASCO guideline endorsement of an ASTRO guideline. J Clin Oncol 39:931-939, 2021.
Originally published in ASCO Daily News. © American Society of Clinical Oncology. ASCO Daily News, January 28, 2021. All rights reserved.
