# The Role of Dosimetric Parameters in Radiation Pneumonitis: A Functional Approach in Adjuvant Treatment of Malignant Pleural Mesothelioma

## TL;DR

This study examines how dosimetric parameters, especially those accounting for lung function, can predict radiation pneumonitis in mesothelioma patients undergoing radiation therapy.

## Contribution

The study evaluates the added value of functional dosimetric parameters over conventional ones in predicting radiation pneumonitis in mesothelioma patients.

## Key findings

- Acute radiation pneumonitis occurred in 42% of patients, with 28% experiencing moderate-to-severe cases.
- V20 and FCL_V20 were significantly associated with radiation pneumonitis risk.
- A V20 threshold > 1.8% predicted severe radiation pneumonitis with high specificity.

## Abstract

Malignant pleural mesothelioma (MPM) is a very aggressive cancer that is quite rare and is mostly linked to asbestos exposure. In the case of MPM patients undergoing lung-saving surgery (pleurectomy/decortication), radiation therapy forms an integral part of the treatment plan. However, its use is often limited because of the danger of lung toxicity, especially radiation pneumonitis (RP). It is of utmost importance to discover reliable predictors of radiation pneumonitis that can be utilized for personalizing the treatment plan. This retrospective study was conducted to evaluate the prognostic power of conventional dosimetric parameters—the so-called “functional” parameters which are determined by the exclusion of the emphysematous regions of the lungs—in a group of MPM patients receiving adjuvant intensity-modulated radiation therapy. The results in our hands suggest that functional parameters might offer additional value over standard parameters.

Background: Malignant pleural mesothelioma (MPM) is an aggressive neoplasm, the major cause of which is asbestos exposure. Adjuvant radiotherapy after pleurectomy/decortication (P/D) aims at reducing locoregional recurrence but is limited by the risk of radiation pneumonitis (RP). In this study, we attempted to evaluate the predictive value of conventional and functional dosimetric parameters in assessing RP risk. Methods: This retrospective study analyzed 68 patients with non-metastatic MPM treated with adjuvant radiotherapy after P/D. Dosimetric parameters, including V20, V5, and mean lung dose (MLD), were calculated for both total lung volume and functional lung volume (FLV), with emphysematous regions excluded based on CT imaging thresholds. Statistical analyses assessed correlations between these parameters and acute RP incidence. Results: Acute RP developed in 42% of patients, and 28% had moderate-to-severe (Grade 2–3) events. V20 and FCL_V20 were significantly associated with the risk of RP (p = 0.017 and p = 0.028, respectively). Predictive accuracy for conventional V20 (AUC = 0.668) and Functional Contralateral Lung V20 (FCL_V20) (AUC = 0.655) showed moderate efficacy, without further significant improvement in using functional parameters. A V20 threshold > 1.8% predicted severe RP with high specificity (89.8%). Conclusions: While functional lung delineation provides an alternative in dosimetry, conventional V20 is a robust predictor of RP. Optimization of dosimetric constraints, in an effort to reduce pulmonary toxicity in MPM patients, should be further combined with advanced radiotherapy techniques and biomarkers.