2563 - Assessment of Local Control and Pain Relief of Rib Metastases Treated with SBRT

G. Simontacchi¹, M. Loi¹, D. Greto¹, G. Francolini¹, V. Salvestrini², V. Di Cataldo¹, I. Desideri³, M. Casati⁴, M. Zani⁴, R. Doro², L. Masi², P. Bonomo¹, P. Garlatti¹, and L. Livi³; ¹Radiation Oncology, Careggi University Hospital, University of Florence, Florence, Italy, ²Istituto Fiorentino di Cura e Assistenza (IFCA), CyberKnife Center, Florence, Italy, ³Department of Experimental Clinical and Biomedical Sciences “Mario Serio”, University of Florence, Florence, Italy, ⁴Medical Physics, Careggi University Hospital, University of Florence, Florence, Italy

Purpose/Objective(s): Following reports of improved efficacy in vertebral metastases, Stereotactic Body Radiotherapy has been increasingly applied for local palliation and disease control in non-spinal bone metastases. However, its use in the management of rib metastases (RM) has been traditionally limited due to purported risk of iatrogenic fracture, possibly resulting in impaired pain control. For this reason, SBRT in this setting has been scarcely reported in literature. The aim of our study is to evaluate pain control and local failure rates in RM treated with SBRT. Materials/

Methods: We collected data from a cohort of RM patients treated from October 2014 to December 2023 with SBRT. Clinical and treatment-related data were collected. Pain Control (PC) was defined as absence or reduction of pain allowing for decreased medication intake. Local Failure (LF) was defined as radiologic progression on follow-up imaging. Univariable analysis with the log-rank test and multivariable analysis with the Cox model were performed to investigate predictors of PC and LF.
Results: Data from 55 patients accounting for 64 RM were collected. Median age was 70 (range 37-78) years. Most represented primary tumors were prostate (41%,n=26) and non-small cell lung cancer (21%,n=13). Baseline pain before SBRT was reported in 26 (41%) lesions, requiring daily opioid intake in 12 cases (20%). SBRT was delivered with C-arm (92%, n=59) and robotic-arm (8%, n=5) Linac using the following regimens: 16 Gy/1 fraction, 24 Gy/2 fractions, 24-30 Gy/3 fractions, 30-55 Gy/5 fractions. Median EQD2 (assuming an a/ß=10) was 47 Gy (range 35-96.25). Median follow-up was 14 (range 1-76) months. PC was 87% at 6 months and 82% at 1 year. Age> 70 (p=0.002), EQD2 =40 Gy (p=0.009) and baseline pain (p=0.004) were correlated with impaired PC although only EQD2 =40 Gy (p=0.007) and baseline pain (p=0.012) proved significant at multivariate analysis. LF rate was 2.0% at 6 months and 4.8% at 1 year. Median OS was 60 (95%CI 25-70) months. No predictive factors of LF were identified at statistical analysis. Pain flare was observed in 1 patient. No rib fracture and/or skin fibrosis was observed.
Conclusion: SBRT for RM is associated with low rates of local failure and durable pain control. Administration of SBRT before the onset of symptoms and use dose intensive regimens may result in improved pain control .