Musculoskeletal
Pigmented villonodular synovitis (diffuse TGCT)
An overgrowth of the joint lining where radiation controls diffuse disease that surgery alone cannot clear.
Definition
Pigmented villonodular synovitis (PVNS), now grouped as diffuse-type tenosynovial giant cell tumor (D-TGCT), is a rare proliferation of the synovial lining that fills joints with friable, hemosiderin-laden tissue. It most commonly affects the knee and causes recurrent swelling, effusions, pain, and bleeding, often in young adults. Diffuse disease wraps around the entire joint, making complete surgical removal nearly impossible without sacrificing the joint.
How radiation treats it
Radiation ablates the proliferating synovial lining throughout the joint capsule, including the surgical blind spots behind ligaments and in posterior recesses that recur after synovectomy. Fibrosis of the treated synovium reduces bleeding, effusion, and the destructive erosion of cartilage over time. Adjuvant radiation is used when disease is diffuse, recurrent, or when only subtotal removal was achievable.
Side effects
- Mild acute skin reaction and temporary joint effusion or increased swelling during the treatment course.
- Stiffness from capsular fibrosis is the main late concern and is managed with range-of-motion exercises.
- In lower-extremity treatment, careful dose constraints minimize volume of irradiated bone and soft tissue.
Simulation process
The involved joint is CT-simulated with the limb in a reproducible position (usually supine for knees, with a custom leg immobilizer). The clinical target volume includes the entire synovial capsule — anterior and posterior recesses — as defined on contrast-enhanced MRI, which is fused to the planning CT. Skin marks or tattoos are placed near the joint, and organs at risk such as the epiphyses, cartilage, and contralateral limb are contoured. Patient setup is verified with orthogonal images before the first fraction.
Treatment process
A typical regimen is 36–45 Gy delivered in 1.8–2 Gy daily fractions over four to five weeks, following subtotal synovectomy. IMRT or 3D conformal anterior–posterior/posterior–anterior fields cover the whole joint with a small margin. Patients are followed with serial MRI; reduction in synovial thickness and effusion may take six to twelve months to fully manifest.
Key takeaways for students
- Adjuvant RT after subtotal synovectomy for diffuse disease.
- Treat the entire synovial compartment, not just the visible mass.
- Response is measured in months — MRI at follow-up shows progressive synovial regression.