Spinal Cord Re-Irradiation After Prior Palliative Radiotherapy
A 63-year-old man with metastatic NSCLC, prior palliative radiotherapy 30 Gy in 10 fractions to T4-T6 14 months ago for bone metastasis, now presents with new T7-T8 spinal cord compression, ESCC grade 2, severe pain, and inability to walk. MRI shows cord compression at T7-T8. He has 4-month expected survival, ECOG 2, and is on dexamethasone. The team considers 8 Gy in 1 fraction versus 20 Gy in 5 fractions to T7-T8, but the prior T6 field overlaps the new field by 1 cm. The prior plan had spinal cord Dmax 32 Gy. The cumulative spinal cord dose is unknown. He has thrombocytopenia (platelets 70,000/µL) and a history of peptic ulcer disease. He is not a surgical candidate, and his pain is poorly controlled with opioids.
1. Calculate the EQD2 for the prior course and for each proposed regimen using an α/β of 2 Gy for spinal cord, and interpret the cumulative risk.
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Using α/β = 2 Gy for spinal cord: EQD2 = total dose × (d + α/β)/(2 + α/β). Prior 30 Gy/10: d = 3 Gy, EQD2 = 30 × (3+2)/4 = 37.5 Gy. If the cord Dmax was 32 Gy, the cord maximum EQD2 is 32 × 5/4 = 40 Gy. Proposed 8 Gy/1: d = 8 Gy, EQD2 = 8 × (8+2)/4 = 20 Gy; cumulative with prescribed prior = 57.5 Gy (or 60 Gy using Dmax). Proposed 20 Gy/5: d = 4 Gy, EQD2 = 20 × (4+2)/4 = 30 Gy; cumulative = 67.5 Gy (or 70 Gy using Dmax). Both exceed the commonly cited cord tolerance of 50 Gy EQD2, and 20 Gy/5 exceeds it substantially. The overlap is only 1 cm, so the cumulative dose to the entire cord is not uniform; the highest risk is at the overlap. Still, the calculation shows that a second course is not radiobiologically trivial.
2. Given the overlap and performance status, which regimen would you recommend and why? Include what you would document and monitor.
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Given ECOG 2, 4-month survival, poor pain control, thrombocytopenia, and prior high cord dose, I would recommend 8 Gy in 1 fraction to T7-T8 with careful image guidance and a sharp field edge at the overlap. The goal is rapid palliation, not long-term local control; single-fraction radiotherapy is effective for pain and cord compression in poor-prognosis patients and minimizes treatment burden. 20 Gy in 5 fractions would add 30 Gy EQD2 to a cord already at 37.5–40 Gy EQD2, raising myelopathy risk without a survival benefit. If the patient were a surgical candidate or had longer prognosis, decompression and stabilization plus 20 Gy/5 might be considered, but not here. Document the prior dose, overlap, EQD2 calculation, informed consent about myelopathy, dexamethasone taper, platelet count, and ulcer prophylaxis. Monitor neurologic function and pain; avoid NSAIDs.