Y. Shindo1,2, Y. Koide1, N. Nagai1,2, T. Kitagawa1, T. Aoyama1, H. Shimizu1, S. Hashimoto1, H. Tachibana1, and T. Kodaira1; 1Department of Radiation Oncology, Aichi Cancer Center Hospital, Nagoya, Japan, 2Department of Radiology, Nagoya University Graduate School of Medicine, Nagoya, Japan
Purpose/Objective(s): We aimed to assess the efficacy and safety of stereotactic body radiation therapy (SBRT) in treating oligometastatic non-spine bone metastases (NSBM). Materials/
Methods: This retrospective study analyzed patients treated with SBRT for oligometastatic NSBM at two centers between 2019 and 2023. The oligometastatic disease was defined as a limited number of 3 or fewer metastases in this study. The NSBM lesions were categorized into the pelvis (excluding the sacrum), ribs, shoulders, and others. The primary endpoint was the local failure (LF) and pathologic fracture (PF) rates. Secondary endpoints included overall survival (OS) and other adverse events based on the Common Terminology Criteria for Adverse Events, version 5.0. Cumulative incidence with death as a competing event was used to assess rates of LF and PF at 1 and 2 years. Results: Among the 61 lesions from 55 patients screened, 43 oligometastatic NSBM lesions from 38 patients met the criteria. The median patient age was 65, and major primary cancers included the prostate (30%), gastrointestinal (16%), and lung (14%). When the oligometastatic lesion was diagnosed, 20% were painful lesions, 80% were asymptomatic, and 50% were on systemic therapy (i.e., oligoprogression). SBRT targeted lesions in the pelvis (53%), ribs (23%), and shoulders (5%), and the dose prescription was used with 30–35 Gy in 5 fractions (79%), 27 Gy in 3 fractions (5%), and 24 Gy in 2 fractions (7%). The number of target lesions was one (87%), two (10%), and three (3%). In a median follow-up time of 16.8 months (range: 2.7–54.7 months), 5 LFs (3 in the pelvis, 1 in the rib, and 1 in the others) and 6 PFs (3 in the pelvis and 3 in the rib) were recorded. All the PF lesions were grade 1 and did not require any treatment. The cumulative incidence of LF at 1 and 2 years was 10.4% (95% CI: 3.1–22.7%) and 15.1% (95% CI: 4.9–30.4%), respectively. The cumulative incidence of PF at 1 and 2 years was 7.8% (95% CI: 1.9–19.3) and 15.2% (95% CI: 5.2–30.1), respectively. The 1-year and 2-year OS were 89.5% (95% CI: 74.3–95.9%) and 73.5% (95% CI: 53.0–86.1), respectively. The recorded adverse events included 1 case of nausea (Grade 1) and 2 cases of dermatitis (Grade 2). No events of grade 3 or higher were observed. Conclusion: The results of this study may confirm the high efficacy and tolerable toxicity of SBRT for oligometastatic NSBM, highlighting the need for future clinical trial enrollment.
