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Radionuclide therapy for bone metastases — Ra-223, Sm-153, Sr-89
Agents that mimic calcium or bind to bone being formed accumulate around osteoblastic metastases and irradiate them at close range — Ra-223 (an alpha emitter) prolongs life in prostate cancer, while Sm-153 and Sr-89 (beta emitters) relieve pain only.
Why it matters in the exam
The exam asks about contraindications and patient selection. Ra-223 is intended for metastatic castration-resistant prostate cancer with symptomatic bone metastases and no visceral metastases; in ALSYMPCA it prolonged overall survival. The dose: 55 kBq/kg every 4 weeks, 6 injections. Before the first dose, neutrophils of at least 1.5×10⁹/L, platelets of at least 100×10⁹/L and haemoglobin of at least 10 g/dL are required; before later doses — neutrophils of at least 1.0×10⁹/L and platelets of at least 50×10⁹/L.
Visceral metastases (liver, lungs) are a reason not to give Ra-223, and it should not be combined with abiraterone and prednisone because of the increase in fractures and deaths seen in the ERA 223 trial; a bone-protecting drug is recommended. Ra-223 is excreted mainly through the bowel, so diarrhoea, inflammatory bowel disease or bowel obstruction need caution. The range of alpha particles is less than 0.1 mm, so marrow toxicity is relatively low. The half-life is 11.4 days.
Sm-153 EDTMP (half-life about 46 hours) and Sr-89 (about 50 days) relieve pain from osteoblastic metastases of various tumours (prostate, breast), provided bone scintigraphy shows uptake in the painful lesions. Relief appears within 1–3 weeks, and sometimes there is a temporary "pain flare" in the first two to three days. Contraindications: marrow suppression or DIC, severe renal failure, pregnancy, and above all spinal cord compression or an impending pathological fracture — situations that require external radiotherapy or surgery, not systemic treatment.
Key points
- Ra-223 — alpha, prolongs life in mCRPC with bone metastases.
- 55 kBq/kg every 4 weeks, 6 injections.
- Not with visceral metastases and not with abiraterone and prednisone.
- Sm-153 and Sr-89 — pain relief only.
- Cord compression — external radiotherapy or surgery.
Summary table
| Agent | Emission and half-life | Indication | Key point |
|---|---|---|---|
| Ra-223 | Alpha, 11.4 days | mCRPC with symptomatic bone metastases | Prolongs life; not with visceral metastases |
| Sm-153 EDTMP | Beta, about 46 hours | Pain from osteoblastic metastases | Pain flare |
| Sr-89 | Beta, about 50 days | Pain from osteoblastic metastases | Prolonged marrow suppression |
| External radiotherapy | — | Focal pain, cord compression | Preferred in an emergency |
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Sources
- EANM Guideline for Radionuclide Therapy with Radium-223 of Metastatic Castration-Resistant Prostate Cancer, 2018 — Patient selection, haematological criteria and administration
- EANM Procedure Guidelines for Treatment of Refractory Metastatic Bone Pain, 2008 — Sr-89 and Sm-153 indications and contraindications
- ALSYMPCA Phase 3 Trial of Radium-223 Dichloride, 2013 — Eligibility and outcomes
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.