The Treatment Outcomes of Stereotactic Body Radiotherapy for Bone Oligo-Metastatic Disease.

Purpose/Objective(s) Stereotactic body radiotherapy (SBRT) has been increasingly expected to be a treatment option for bone metastases, especially in oligometastatic disease (OMD). This study aimed to clarify the efficacy of SBRT for bone oligo-metastases. Materials/Methods Patients who met the following criteria were retrospectively reviewed from a prospective database; 1) with bone metastases, 2) treated with SBRT for bone metastases and 3) with active lesion less than 5 in 3 different sites. OMD was defined as the patients with active lesion less than 5 in 3 different sites. Progression free survival (PFS), local failure (LF), overall survival (OS) and adverse events (AEs) were evaluated. LF was estimated using the cumulative incidence function adjusted for the competing risk of death. AEs were evaluated based on Common Terminology Criteria for Adverse Events 5.0. Results There were 219 cases in 188 patients selected from our database showed: median age, 66 years (range, 23-85 years); performance status, 0/1/2/3/4, 123/74/13/6/3; lesion histopathology, lung/prostate/ colorectal/breast/thyroid/kidney/others, 35/31/22/21/21/21/68; region of bone metastases, spine/non-spine, 139/80; number of metastases, 1/2/3/4/5, 146/45/20/6/2; type of OMD, synchronous OMD/metachronus OMD/repeat OMD/induced OMD, 39/93/64/23; treatment for primary site, local therapy/systemic therapy/none, 196/20/3; systemic therapy before SBRT, yes/no, 96/123; systemic therapy after SBRT, yes/no/unknown, 105/111/3; median interval from upfront treatment, 36 months (range, 1-300 months); radiotherapy history for targeted lesion, yes/no, 49/170; the prescribed dose, 20 Gy in single fraction/24 Gy in 2 fractions/30 Gy in 5 fractions/35 Gy in 5 fractions, 9/121/21/68. Median follow-up after SBRT was 16 months (range, 1-82 months). The 1-year PFS rate, LF rate and OS rate were 43.1%, 12.8% and 89.7%, respectively. The median PFS was 11 months. Most dominant first failure pattern was another bone metastasis. In univariate analysis of PFS, good performance status (P = 0.028), metastasis from prostate cancer (P = 0.00052) and longer interval from upfront treatment (P = 0.012) were associated with a significant better prognosis. In multivariate analysis, metastasis from prostate cancer (P = 0.010) and interval from upfront treatment (P = 0.019) were independent prognostic factors. In the cases excluding prostate cancer, median PFS was 9 months and the 1-year PFS rate was 39.4%. In 111 cases with treated before December 2018, 2-year progression-free survival was achieved in 22 cases (19.8%). Grade 5 infection, grade 4 radiation myelopathy and grade 3 dermatitis were observed in one case, respectively. Seventeen cases of fracture were encountered. Conclusion SBRT for bone oligo-metastases provided long term systemic disease control in about 20% of cases. SBRT is effective treatment option for bone OMD especially for the cases with long interval from upfront treatment.