Hematologic and other
Splenic irradiation for splenomegaly
Very low daily doses that shrink a painfully enlarged spleen and improve blood counts without removing the organ.
Definition
Splenomegaly — massive spleen enlargement — occurs in myelofibrosis, chronic leukemias, and other hematologic disorders, causing left upper-quadrant pain, early satiety, and cytopenias from hypersplenism (the enlarged spleen traps and destroys blood cells). Splenectomy is high-risk in these patients, and systemic options are limited or exhausted, making symptoms difficult to palliate.
How radiation treats it
Low-dose radiation to the enlarged spleen suppresses the hyperactive splenic macrophages and extramedullary hematopoietic tissue, shrinking the organ, easing pain and fullness, and often improving blood counts. Because patients are frequently pancytopenic, very small daily doses are used — often lower than any other radiation prescription — to avoid precipitating severe cytopenias. The goal is durable symptom palliation and preservation of quality of life.
Side effects
- Cytopenias — the main toxicity; blood counts must be monitored closely during treatment and doses adjusted downward as counts fall.
- Nausea, loss of appetite, or early satiety may briefly worsen.
- A small risk of significant or lasting cytopenia if the regimen is not tailored to the patient's baseline counts.
Simulation process
The patient is positioned supine with arms raised above the abdomen, often with a vacuum-lock cradle. A CT simulation defines the spleen and its margins; in some centers an anterior mark along the costal margin with a simple measured field is used, but CT-based planning is more accurate. The left kidney is contoured and shielded as much as possible. Baseline blood counts must be drawn before treatment begins, and weekly counts are standard during therapy.
Treatment process
Regimens are individualized and intentionally gentle: 0.1–1 Gy per fraction, commonly starting at 0.25 Gy daily, over 2–3 weeks with a total dose of roughly 1–10 Gy, adjusted fraction by fraction according to blood counts and symptom response. Treatment is delivered with simple AP fields. Symptom relief can be rapid and lasts months to years; re-irradiation is possible if symptoms recur.
Key takeaways for students
- Among the lowest daily doses used in radiation therapy — the spleen responds to fractions as small as 0.25 Gy.
- Blood counts drive every decision; treat gently, watch weekly.
- A palliative alternative to high-risk splenectomy.