# Stereotactic Re-irradiation of Sternal Metastases Using Skin Surface Fiducial Markers and Real-Time Motion Synchronization

## TL;DR

This paper presents a new method using skin markers and real-time motion tracking to safely deliver radiation to sternal metastases, with results showing pain relief and control in patients.

## Contribution

A novel approach using skin fiducial markers and real-time motion synchronization for stereotactic re-irradiation of sternal metastases is introduced.

## Key findings

- Two patients with sternal metastases achieved complete pain relief and durable local control using the described method.
- Late toxicity was not observed in one patient, while another developed potential cardiac issues linked to cumulative radiation.
- The study highlights the importance of minimizing cardiac dose to reduce long-term toxicity in re-irradiation cases.

## Abstract

Due to respiratory motion, treating sternal metastases with stereotactic body radiotherapy (SBRT) is challenging, often requiring large irradiation volumes to account for target movement. To address this, we implemented a straightforward approach by placing skin fiducial markers near the sternal metastasis, enabling real-time motion synchronization with the CyberKnife® System (Accuray Inc., Sunnyvale, CA). Advances in anti-cancer therapies have significantly extended survival in metastatic patients, increasing their likelihood of requiring re-irradiation and experiencing late toxicities. We present the outcomes of two patients, one with metastatic hepatocellular carcinoma (mHCC) and one with metastatic breast cancer (mBC), who underwent two courses of SBRT for sternal metastases using the CyberKnife® and skin fiducial markers for motion management. Both patients tolerated the treatment well, achieving complete pain relief and durable local control. No late toxicity was observed in the mHCC case, while the mBC patient developed significant left anterior descending artery (LAD) stenosis, which may have been linked to cumulative radiation exposure. Given the known risk of cardiac toxicity associated with radiation therapy, these findings underscore the importance of minimizing cardiac dose to reduce long-term toxicity, particularly in re-irradiation cases.