Could conventionally fractionated radiation therapy coupled with stereotactic body radiation therapy improve local control in bone oligometastases? Évaluation du contrôle local des oligométastases osseuses traitées par irradiation stéréotaxique seule ou associée à une irradiation conformationnelle de fractionnement classique

Purpose: To describe clinical outcomes of stereotactic body radiation therapy (SBRT) applied alone or as a boost after a conventionally fractionated radiation therapy (CFRT) for the treatment of bone oligometastases. Material and Methods: This retrospective cohort study included patients treated with SBRT from January 2007 to December 2015 in the Institut de cancérologie de Lorraine in France. The inclusion criteria involved adults treated with SBRT for one to three bone metastases from a histological proven solid tumor and a primary tumor treated, an Eastern Cooperative Oncology Group (ECOG) score inferior or equal to 2. Local control (LC), overall survival (OS), progression free survival (PFS), bone progression incidence (BPI), skeletal related events free survival (SRE-FS), toxicity and pain response were evaluated. Results: Forty-six patients and 52 bone metastases were treated. Twenty-three metastases (44.2%) received SBRT alone mainly for non-spine metastases and 29 (55.8%) a combination of CFRT and SBRT mainly for spine metastases. The median follow-up time was 22 months (range: 4–89 months). Five local failures (9.6%) were observed and the cumulative incidences of local recurrence at 1 and 2 years respectively were 4.4% and 8% with a median time of local recurrence of 17 months (range: 4–36 months). The one- and two-years OS were 90.8% and 87.4%. Visceral metastasis (HR: 3.40, 95% confidence interval [1.10–10.50]) and a time from primary diagnosis (TPD) > 30 months (HR: 0.22 [0.06–0.82]) were independent prognostic factors of OS. The 1 and 2 years PFS were 66.8% and 30.9% with a median PFS time of 18 months [13–24]. The one- and two-years BPI were 27.7% and 55.3%. In multivariate analysis, unfavorable histology was associated with worse BPI (HR: 3.19 [1.32–7.76]). The SRE-FS was 93.3% and 78.5% % at 1 and 2 years. The overall response rate for pain was 75% in the evaluable patients (9/12). No grade ≥ 3 toxicity nor especially no radiation induced myelopathy (RIM), two patients developed asymptomatic vertebral compression fractures. Conclusion: The sole use of SBRT or its association with CFRT is an efficient and well-tolerated treatment that allows high LC for bone oligometastases.