Impact of Heart Dose on Survival in Palliative Radiotherapy for Bone Metastases: Propensity Score-matched Analysis

Although the effects of varying heart doses on overall survival (OS) in curative thoracic radiotherapy have been investigated, their impact in palliative settings remains underexplored. This study aimed to examine the impact of heart dose on OS in patients with bone metastases treated with palliative radiotherapy over a three-year follow-up period.

This study included 303 patients who underwent palliative radiotherapy for bone metastases between 2013 and 2022. The primary endpoint was OS, which was evaluated over a fixed three-year follow-up period. To adjust for baseline confounders between patients with and without mean heart dose (MHD) ≥5Gy, we performed 1:1 propensity score matching (PSM) using the following variables: performance status (PS); primary tumor type; number of bone metastases; number of distant metastases (visceral organs, non-regional lymph nodes, and serosal surfaces such as the pleura and peritoneum).

A total of 108 of 303 patients were included after PSM, with 54 patients each in the groups with and without MHD ≥5 Gy. After matching, the baseline characteristics used as matching variables were well balanced, with no significant differences between the groups according to the chi-square test. Kaplan-Meier analysis demonstrated significantly poorer OS in patients with MHD ≥5 Gy than in those without (p=0.016); annualized event rates for OS were 30.2% and 21.6% in patients with and without MHD ≥5 Gy, respectively.

In propensity score-matched patients receiving palliative, but not curative, radiotherapy, higher MHD was significantly associated with poorer OS over a three-year follow-up period. Furthermore, in the palliative cohort, the MHD level associated with OS may be lower than that in the curative setting.