Analysis of major joint dosimetry based on a standardized contouring method among patients with extremity soft tissue...

Contemporary radiation treatment planning for extremity soft tissue sarcoma incorporates major joint space dose constraints. However, interpretation of historical dosimetric data and implementation of constraints is limited by the absence of standardized contouring guidelines.

Guidelines were developed for the shoulder, elbow, hip, and knee joints using anatomic references and input from sarcoma radiation oncologists, a musculoskeletal radiologist, and orthopedic oncologists. These guidelines were retrospectively applied to patients with extremity sarcoma treated with combined surgery and radiation at a single academic institution. Dosimetric parameters were computed and CTCAE v6 grading was used to evaluate for joint stiffness and arthralgia. Dose-toxicity relationships were evaluated using Wilcoxon rank-sum testing and logistic regression with receiver operator curve analysis.

Of 97 patients treated with pre- or post-operative radiation, 61 (62.9%) patients had planning target volume co-planar with 66 joints on axial imaging. Average joint volumes were: shoulder 76 mL (range 57-105 mL), elbow 51 mL (39-71 mL), hip 92 mL (66-130 mL), and knee 305 mL (213-455 mL). Grade ≥2 joint stiffness developed in 8 joints (14.8%) and grade ≥2 arthralgia in 2 joints (3.7%). Joints with Grade ≥2 stiffness received significantly higher mean doses (3096 cGy vs 1784 cGy, p=0.01) and D50% doses (3048 cGy vs 1462 cGy, p=0.007). The median joint dose (D50%) demonstrated the highest area under the curve for predicting joint stiffness among evaluated dosimetric parameters (AUC=0.7935).

Standardized contouring guidelines for major joints were developed and demonstrated clinically relevant dose-toxicity relationships. These guidelines will be prospectively employed in the upcoming phase III SWOG trial S2505 and can inform treatment planning strategies to minimize joint morbidity in extremity sarcoma patients.