What is the recommended dose and volume for thoracic radiotherapy in a patient with small cell lung cancer with a peripheral primary, mediastinal N2 nodes, and a single RP nodal metastasis, who has achieved a very good partial response to carboplatin and etoposide?

Thoracic Radiotherapy for ES-SCLC with Excellent Response to Chemotherapy

Recommended Dose and Fractionation

For this patient with extensive-stage SCLC (due to the single retroperitoneal nodal metastasis) who achieved a very good partial response to carboplatin-etoposide, consolidative thoracic radiotherapy should be delivered to a dose of 30 Gy in 10 fractions (once-daily) targeting the post-chemotherapy residual disease volume. 1

This scenario represents extensive-stage disease despite the limited thoracic involvement, as the retroperitoneal nodal metastasis places the patient outside the boundaries of a single radiation port. 1

Target Volume Definition

The radiation field should be based on post-chemotherapy volumes (residual disease), not pre-chemotherapy volumes. 1

• Target the residual small hilar node and any other sites of initial involvement that have not completely resolved 1
• Include the post-chemotherapy mediastinal N2 nodal regions if there was significant initial involvement, even if now resolved 1
• The retroperitoneal nodal site should be evaluated separately; if it has also responded well, it may be included in a consolidative approach, though this is less well-established 1

Key Distinctions from Limited-Stage Disease

This case differs fundamentally from limited-stage SCLC management:

• Limited-stage SCLC receives concurrent chemoradiotherapy with higher doses (45 Gy twice-daily or 60-70 Gy once-daily) 1
• Extensive-stage SCLC with good response receives consolidative (sequential) thoracic RT at lower doses after chemotherapy completion 1

The evidence for extensive-stage consolidation comes from trials showing benefit in patients achieving good response to initial chemotherapy, using moderate doses around 30 Gy. 1

Rationale for Post-Chemotherapy Volume

Treating post-chemotherapy volumes in this extensive-stage setting is appropriate because:

• The patient has already received 6 cycles of systemic therapy with excellent response 1
• Pre-chemotherapy volumes would be unnecessarily large and increase toxicity without proven benefit in the extensive-stage setting 1
• The goal is consolidation of residual disease, not definitive concurrent treatment 1

Additional Considerations

Prophylactic cranial irradiation (PCI) should be strongly recommended given the very good partial response to chemotherapy. 1 PCI reduces brain metastases and improves survival in responding extensive-stage SCLC patients. 1

Common pitfall to avoid: Do not apply limited-stage SCLC radiation doses (45-70 Gy) to this extensive-stage patient, as the presence of the retroperitoneal nodal metastasis definitively classifies this as extensive disease requiring a different treatment paradigm. 1

Timing: Consolidative thoracic RT should be delivered after completion of chemotherapy and confirmation of response, typically within 4-6 weeks of completing systemic therapy. 1