Re-irradiation of a painful vertebral metastasis with a prior cord dose
A 55-year-old woman with hormone receptor-positive metastatic breast cancer has a painful T8 vertebral metastasis. Fourteen months ago she received 30 Gy in 10 fractions to T7–T9 for a different lesion; the spinal cord maximum was 27 Gy. MRI now shows a new T8 lesion with epidural disease but no cord compression. She is opioid-tolerant, has controlled pain at rest but severe pain on movement, and has no neurological deficit. You are asked to prescribe palliative radiotherapy. The trainee proposes 20 Gy in 5 fractions to T8 and asks whether the previous course matters because 'the cord tolerance is 50 Gy.'
1. Calculate the EQD2 for the previous spinal cord dose and for the proposed 20 Gy/5 fraction course if the cord received the full dose. What does this tell you about the trainee's statement?
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The trainee is adding nominal doses, which is misleading. For late cord effects, use α/β = 2 Gy. Prior cord maximum 27 Gy in 10 fractions (2.7 Gy/fraction): EQD2 = 27 × (2.7 + 2)/(2 + 2) = 31.7 Gy. If the new 20 Gy/5 plan delivered the full 20 Gy to the cord (4 Gy/fraction), EQD2 = 20 × (4 + 2)/(2 + 2) = 30 Gy. The cumulative cord EQD2 would be about 61.7 Gy, not 47 Gy nominal. The '50 Gy tolerance' statement is therefore an oversimplification: the actual cord dose will be lower than the prescription, but a composite plan is required. The interval of 14 months and the prior cord dose matter, and re-irradiation tolerance is uncertain.
2. How would you plan and prescribe radiotherapy, and what cord constraint would you use?
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I would not prescribe 20 Gy/5 without a composite plan. I would fuse the prior and current CT scans, calculate the cumulative cord EQD2, and ask the planner to keep the cord as low as reasonably achievable. If cumulative cord EQD2 can be kept near or below 50 Gy, a short palliative course may be reasonable; if not, I would consider 8 Gy in one fraction, which is effective for painful bone metastases and reduces the number of fractions, or a smaller per-fraction dose. I would also consider vertebral augmentation, optimal analgesia and systemic therapy. Because there is epidural disease but no cord compression, I would monitor for neurological symptoms and involve spine surgery if instability develops. The plan and constraints would be documented and discussed at MDT.
3. What would you tell her about benefits, risks, and alternatives?
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I would explain that radiotherapy relieves pain in most patients, often within 2–4 weeks, but the response is not immediate and she may need continued analgesia. The main serious concern is radiation myelopathy, which is rare but catastrophic and risk increases with cumulative cord dose, fraction size and a short interval. I would explain that the exact risk is uncertain and that the plan will minimise cord dose. I would compare one fraction versus five, including convenience, travel, pain flare and the small chance of needing further treatment. I would also discuss vertebral augmentation and systemic options. I would confirm her goals, use an interpreter if needed, and document informed consent with the uncertainty stated.