KEY POINTS
- Investigators developed standardized CT-based contouring methods for the shoulder, elbow, hip and knee, using anatomic references plus input from sarcoma radiation oncologists, orthopedic oncologists and a musculoskeletal radiologist.
- Among 97 patients treated with surgery and RT, 61 patients (62.9%) had a PTV coplanar with 66 major joints, illustrating how frequently joint exposure becomes relevant during extremity sarcoma treatment.
- Most patients received preoperative RT and modern conformal treatment. Hypofractionated plans were converted to a 25-fraction equivalent using an α/β of 3 Gy to allow comparison of late joint exposure across schedules.
- Grade ≥2 joint stiffness developed in 14.8% of evaluable joints, while grade ≥2 arthralgia occurred in 3.7%.
- Joints developing grade ≥2 stiffness received substantially higher mean dose: 30.96 Gy versus 17.84 Gy. D50% showed an even clearer separation at 30.48 Gy versus 14.62 Gy.
- Among the tested dosimetric metrics, joint D50% had the strongest discrimination for stiffness, with AUC 0.7935, followed closely by D60% and mean joint dose.
- These values are planning benchmarks rather than hard constraints. Joint stiffness is multifactorial, including surgery, wound complications and soft-tissue deficits, and the authors specifically caution against compromising target coverage to spare the joint.
CLINICAL TAKEAWAY
For extremity sarcoma close to a major joint, this study offers a practical way to contour the joint consistently and suggests that D50% may be a useful metric to watch during optimization. The dose-toxicity relationship remains retrospective and single-institutional, so these values should guide planning awareness rather than function as validated dose constraints.