Hematologic and other
Langerhans cell histiocytosis (bone lesions)
A rare immune-cell disorder where small radiation doses heal painful bone lesions in children and adults.
Definition
Langerhans cell histiocytosis (LCH) is a clonal proliferation of abnormal dendritic (Langerhans) histiocytes that form lesions in bone, skin, lymph nodes, and rarely the hypothalamic-pituitary region. Isolated bone lesions — classically in the skull, spine, femur, or pelvis — cause localized pain and swelling, and vertebral involvement can lead to collapse (vertebra plana). It can occur at any age, from infants to adults.
How radiation treats it
Low-dose radiation eliminates the pathologic histiocytes within the bony lesion, allowing normal bone remodeling and healing. Response rates are remarkably high — LCH bone lesions are among the most radiosensitive of all benign entities. Radiation is used for lesions that fail to respond to curettage or steroids, lesions in sites that cannot be operated on (spine, skull base), or persistent painful solitary lesions.
Side effects
- Acute skin erythema is the main acute effect and is mild at these low doses.
- In growing children, the treated bone carries a theoretical risk of impaired growth if the growth plate is in the field — doses and fields are minimized accordingly.
- With modern low-dose regimens, clinically significant late effects are rare.
Simulation process
Positioning and immobilization depend on the bone involved: a thermoplastic mask for skull lesions, supine positioning with a vacuum-lock for pelvic or lower-extremity lesions, and arms-over-head positioning for skull-base or spinal targets. CT simulation (fused with MRI, which defines the lytic lesion better than CT) is standard, and in children the sedation and setup are coordinated with child-life services. The target is the lytic bone lesion with a small margin, with nearby growth plates contoured.
Treatment process
Total doses of 6–15 Gy in 1.5–2 Gy daily fractions are typical — far lower than for malignant bone tumors. Simple 3D conformal or electron fields suffice for most lesions. Pain relief often begins within one to two weeks, and bone healing continues for months afterward, confirmed on follow-up imaging. Multifocal or multisystem disease is treated primarily with systemic chemotherapy, with radiation reserved for refractory focal lesions.
Key takeaways for students
- Extremely radiosensitive — 6–15 Gy is enough.
- Best reserved for refractory or surgically inaccessible lesions (spine, skull).
- In children, minimize dose and keep growth plates out of the field.