Osteosarcoma Stereotactic Body Radiotherapy: Factors Associated with Local Failure

Objectives

Stereotactic body radiotherapy (SBRT) is a noninvasive ablative radiotherapy tool that can be beneficial for sarcoma. Outcomes of SBRT for metastatic or recurrent osteosarcoma are not well known. We sought to understand factors associated with local failure.

Methods

Patient, tumor, and treatment factors were collected from an IRB-approved sarcoma SBRT registry and assessed for impact on local failure. Dosimetric analysis was performed to determine patterns of failure. Definition of recurrences: In-field: >80% of recurrent volume within the 95% isodose line, marginal: 20% to 80% of recurrent volume within 95% isodose line, out of field: <20% of recurrent volume within 95% isodose line. Estimates of local failure were determined using the Kaplan-Meier method. Local failure was determined on a per-lesion basis.

Results

A total of 24 patients with metastatic osteosarcoma received SBRT to a total of 71 lesions. Median age was 18 and KPS 90. Median number of lesions treated per patient was 4 (R:1-14). Median dose used was 40Gy over 5 fractions, BED₄ was 120Gy. Median imaging follow up was 9.5 months. Targets included: 47 bone (extremity: 12, spine: 24, other: 11), 11 lung, 12 soft tissue, and 1 liver. Median PTV was 36 cc (R: 3-623 cc). Concurrent therapy was given for 57 lesions (75%). Eleven of 71 lesions (15.5%) failed locally. 6- and 12-month local failure was 10.3% and 13.6%, respectively. Type of local failure included in-field in 4, marginal in 3, and out of field in 4. Median SBRT dose for lesions that failed was 35Gy over 5 fractions. Spine targets and PTV size were significantly associated with local failure on both UVA and MVA.

Conclusion

SBRT for metastatic osteosarcoma results in durable control. Larger PTV size and spine location are associated with local failure in our series. Further study is warranted.