# Organs at risk proximity in central lung stereotactic ablative radiotherapy: A comparison of four-dimensional computed tomography and magnetic resonance-guided breath-hold delivery techniques

## TL;DR

This study compares two techniques for treating central lung tumors and finds that breath-hold MR-SABR increases the distance between the tumor and sensitive organs, reducing potential toxicity.

## Contribution

The study introduces a direct comparison of OAR proximity in 4D-CT and MR-guided breath-hold SABR for central lung tumors.

## Key findings

- Breath-hold MR-SABR increases PTV-OAR distance by 3.7 mm near airways.
- For lesions near the pericardium, PTV-OAR separation increases by 2.0 mm with breath-hold.
- MR-guided breath-hold SABR shows advantages in reducing OAR exposure for central lung tumors.

## Abstract

Higher toxicity rates are associated with stereotactic ablative radiotherapy (SABR) to central lung tumors. Breath-hold (BH) magnetic resonance-guided SABR (MR-SABR) can reduce doses to organs at risk (OAR). We quantified the planning target volumes (PTV) to OAR distance in 45 lesions treated using MR-SABR and generated a corresponding four-dimensional computed tomography (4D-CT) based PTV (motion-encompassing internal target volume plus 5 mm). For lesions located ≦3 cm from airways, BH MR-SABR increased the median PTV distance to OAR by 3.7 mm. For lesions ≦3 cm from pericardium, median PTV-OAR separation increased by 2.0 mm with BH. These findings highlight the advantage of BH SABR for central lung tumors.