# Role of functional mapping on Gallium-68 perfusion positron emission tomography and computed tomographic imaging (PET/CT) to assess the risk of long-term radiation-induced lung toxicity after stereotactic body radiation therapy

## TL;DR

This study shows that using functional imaging improves the prediction of long-term lung damage after radiation therapy for lung tumors.

## Contribution

Functional dosimetric parameters from perfusion PET/CT outperform anatomical ones in predicting radiation-induced lung toxicity.

## Key findings

- Functional parameters in FV50% and FV70% were significantly higher in patients with long-term RILT.
- Anatomical and low functional volume parameters did not differ between patients with and without RILT.
- Functional imaging could guide radiotherapy planning to reduce long-term toxicity risk.

## Abstract

•SBRT is a real alternative treatment for inoperable lung tumors but remains associated with significant pulmonary toxicity.•Perfusion PET/CT imaging is a very attractive test for functional lung avoidance during radiotherapy planning.•This prospective study compare anatomical and functional dosimetric parameters to predict the risk of long-term RILT.•The predictive value of functional parameters outperforms the standard parameters for the risk of grade ≥2 long-term RILT.•Functional parameters could be useful to guide radiotherapy planning to reduce the risk of long-term RILT.

SBRT is a real alternative treatment for inoperable lung tumors but remains associated with significant pulmonary toxicity.

Perfusion PET/CT imaging is a very attractive test for functional lung avoidance during radiotherapy planning.

This prospective study compare anatomical and functional dosimetric parameters to predict the risk of long-term RILT.

The predictive value of functional parameters outperforms the standard parameters for the risk of grade ≥2 long-term RILT.

Functional parameters could be useful to guide radiotherapy planning to reduce the risk of long-term RILT.

To compare the performance of anatomic and functional dosimetric parameters based on Gallium-68 lung perfusion positron emission tomography and computed tomographic imaging (PET/CT) imaging to predict the risk of symptomatic long-term radiation-induced lung toxicity (RILT) in patients with lung tumors treated with stereotactic body radiation therapy (SBRT).

We have performed a prospective study in patients treated with SBRT. Mean dose (MD) and volumes receiving xGy were calculated in five lung volumes: the conventional anatomical volume (AV) delineated on CT images, three lung functional volumes defined on lung perfusion PET imaging (FV50%, FV70%, FV90%, i.e. the minimal volume containing 50 %, 70 % and 90 % of the total activity within the AV), and a low functional volume (LFV = AV-FV90%). The primary endpoint of this analysis was grade ≥2 long-term RILT at 12 months as assessed with NCI CTCAE v.5. The predictive value of anatomical and functional dose volume parameters was evaluated by comparing patients with and without long-term RILT.

Out of the 59 patients included, 50 were still alive at 12 months and 9 (18 %) had grade ≥2 long-term RILT. The MD and the VxGy in the AV and LFV were not statistically different in patients with and without long-term RILT (p > 0.05). All functional parameters in FV50% and FV70% were significantly higher in long-term RILT patients (p < 0.05).

The predictive value of PET perfusion-based functional parameters outperforms the standard CT-based dose-volume parameters for the risk of grade ≥2 long-term RILT.