# Irradiated tumor volume as a predictor of local recurrence and radionecrosis in lung cancer with brain metastases treated with stereotactic radiosurgery

## TL;DR

This study shows that the size of a brain tumor treated with radiosurgery affects the risk of complications or recurrence in lung cancer patients.

## Contribution

The study identifies irradiated tumor volume as a predictor of radionecrosis and local recurrence after radiosurgery for brain metastases.

## Key findings

- Larger tumor volumes significantly increase the risk of radionecrosis and local recurrence after SRS.
- Smaller tumor volumes can lead to delayed complications or recurrence, visible by 12 months post-treatment.
- Methionine PET-CT does not offer a significant diagnostic advantage over MRI in differentiating radionecrosis from recurrence.

## Abstract

Stereotactic radiosurgery (SRS) is a standard treatment of brain metastases (BM), but it may lead to radionecrosis (RN) or local recurrence (LR). This study evaluates irradiated tumor volume as a predictor of LR and RN in SRS-treated lung cancer patients with BM.

We retrospectively analyzed 431 lung cancer patients with BM who underwent SRS at Karolinska University Hospital (all-comers, 2009-2020). Associations among irradiated tumor volume and risks of RN, symptomatic RN, and LR at 6 and 12 months were assessed using Cox regression models. Furthermore, we evaluated the diagnostic performance of methionine positron emission tomography–computed tomography (PET-CT) in differentiating RN from LR.

Forty patients (9.3%) developed asymptomatic RN, 36 (8.4%) symptomatic RN, and 67 (15.5%) LR. Larger tumor volumes significantly increased RN and LR risks. At 6 months, a volume of 4.75 cm3 corresponded to an RN risk reaching up to 20%. By 12 months, substantially smaller volumes were correlated with the same risk levels. Symptomatic RN followed a similar trend, at 6 months and 12 months. A 20% risk of LR was observed with volumes of 5.66 cm3 and 3.28 cm3 at 6 months and 12 months, respectively. Methionine PET-CT had a sensitivity of 0.909 and specificity of 0.600 in detecting RN or LR, with no significant diagnostic advantage compared with magnetic resonance imaging (MRI).

Larger irradiated tumor volumes were correlated with increased RN or LR risk. Smaller volumes can lead to RN and LR, not evident at 6 months, but emerging by 12 months after SRS. Methionine PET-CT showed high sensitivity but modest specificity and offered no significant benefit over MRI in differentiating RN from LR.

CNS metastases volume: a predictor for recurrence and radionecrosis. Created in BioRender. Ekman, S. (2025) https://BioRender.com/c15s098. CNS, central nervous system; MET-PET, methionine positron emission tomography–computed tomography; MRI, magnetic resonance imaging; SRS, stereotactic radiosurgery.

•Brain metastases from lung cancer face risks of RN and recurrence after SRS.•Irradiated tumor volume predicts RN and local failure in SRS-treated CNS metastases.•Small volumes can cause delayed RN and LR, seen by 12 months after SRS.•Methionine PET-CT showed no clear advantage over MRI in differentiating local recurrence from RN.

Brain metastases from lung cancer face risks of RN and recurrence after SRS.

Irradiated tumor volume predicts RN and local failure in SRS-treated CNS metastases.

Small volumes can cause delayed RN and LR, seen by 12 months after SRS.

Methionine PET-CT showed no clear advantage over MRI in differentiating local recurrence from RN.