3532 - Clinical Outcomes of SBRT for Oligometastatic Bone Disease and the Risk Factor of Local Recurrence
Presenter(s)
K. Shirai1,2, M. Endo1, S. Takahashi1, K. Ogawa1, M. Nakagawa1, D. Nagase1, K. Akahane2, M. Kawahara2, Y. Fukuda2, Y. Takahashi2, C. Shibayama1, and M. Nakamura1; 1Department of Radiology, Jichi Medical University Hospital, Shimotsuke, Japan, 2Department of Radiology, Jichi Medical University Saitama Medical Center, Saitama, Japan
Purpose/Objective(s): Chemotherapy is the first-line treatment for distant metastases; however, in cases of oligometastasis (a limited number of metastases), the addition of local treatments such as stereotactic body radiotherapy (SBRT) is expected to improve treatment outcomes. We analyzed the treatment outcomes of oligometastatic bone metastases treated with SBRT at our institution and evaluated the risk factors for local recurrence.
Materials/Methods: This study included 58 patients with 68 bone metastatic lesions who underwent SBRT at our institution between March 2021 and December 2023. The distribution of bone metastases was as follows: a single site in 50 patients, two sites in six patients, and three sites in two patients. Additionally, single brain metastasis, muscle metastasis, and primary tumor recurrence were observed in one patient each, all of which were treated with local therapy. There were 25 cases of induced oligometastasis, 23 cases of metachronous oligometastasis, and 10 cases of repeat oligometastasis. The median patient age was 69 years, with 42 males and 16 females. All lesions were treated with SBRT, with 42 patients receiving radiation dose of 24 Gy in 2 fractions and 16 patients receiving 30–35 Gy in 5 fractions. The most common primary tumor was lung cancer in 22 patients (38%), and the most frequent bone metastatic site was the pelvic bone in 28 lesions (41%).
Results: The median follow-up period for surviving patients was 25 months. Local recurrence after SBRT was observed in 9 patients, with 1- and 2-year local control rates of 89% and 85%, respectively. Disease-specific mortality occurred in 9 patients, while death from other disease was observed in 2 patients. The 1- and 2-year overall survival rates were 95% and 80%, respectively. Among 36 lesions with a gross tumor volume (GTV) of =10 cc, the local recurrence rate was 22%, which was significantly higher than the 3% recurrence rate observed in 32 lesions with a GTV of <10 cc (P<0.01). In multivariate analysis, GTV volume was a statistically significant predictor of local recurrence (P<0.05). Late adverse events included grade 2 radiation pneumonitis in 1 patient and grade 2 pathological fracture in 1 patient, without grade 3 or higher adverse events.
Conclusion: This study showed that SBRT for oligometastatic bone metastases had high local control rates with minimal severe adverse events. However, the local control rate was significantly lower in patients with larger GTV. Further accumulation of cases and long-term follow-up are required to establish the treatment strategies.