2464 - Esophageal Toxicity in Radical Radiotherapy Treatment of Malignant Pleural Mesothelioma

Purpose/Objective(s): This study evaluated the incidence of acute and late esophageal toxicity following Radical Hemithorax Radiotherapy (RHR) in patients with Malignant Pleural Mesothelioma (MPM). Dosimetric parameters associated with the risk of developing esophageal toxicity were also analyzed.

Materials/Methods: A total of 140 patients were enrolled between January 2012 and June 2024. All patients were treated for MPM with a RHR using helical Tomotherapy. The treatment was delivered in 25 daily fractions in accordance with a prescribed scheme comprising a total dose to the PTV/GTV of 50/60 Gy. All patients underwent non-radical surgery and systemic platinum-based doublet therapy before radiation treatment. The cohort characteristics are summarized in table n.1. For the analysis, dose-volume histogram (DVH)-based indices were extracted from the esophagus structure: V30Gy(%), V50Gy(%), D0.1cc(Gy), and Dmean(Gy), D98%(Gy),Volume of the esophagus (cm³) . A correlation index, ISO47.5Gy, was also assessed by classifying patients as positive if the 47.5 Gy isodose fully encompassed the esophageal circumference in at least one axial slice, and negative otherwise. Esophageal toxicity was recorded with the "Common Terminology Criteria for Adverse Events (CTCAE) Ed. 4.0.

Results: Acute esophageal toxicity (AET) was G0-G1 in 45 patients and G2-G3 in 95 patients, with no G4-G5 cases. At the six-month follow-up, dysphagia persisted in two G1 cases, one G2 case, and one G3 case. Beyond six months, only one case of G1 late esophageal toxicity was noted. No significant correlation was found between AET and socio-demographic factors or prior treatments. Significant dosimetric differences were observed between G0-G1 and G2-G3 AET for V30Gy (p=0.005), V50Gy (p=0.003), D0.1cc (p=0.026), and Dmean (p=0.002). ISO47.5Gy was significantly associated with AET severity (p=0.018). In a multivariate analysis accounting for clinical characteristics (sex, tumor side, surgery, and circumferential involvement), V30 >53.3% (p=0.015) and V50 >7.6% (p=0.028) were found to be statistically significant predictors.

Conclusion: No treatment was interrupted due to esophageal toxicity, and no patient required hospitalization during radiation therapy. Dysphagia was primarily an acute event, resolving within six months in most cases. Among the dosimetric parameters, V30(%) and V50(%) were the strongest predictors of esophageal toxicity.