Temporal heart dose variations during IMPT for esophageal cancer and the impact of an adaptation protocol.

Abstract

PurposeIn intensity-modulated proton therapy (IMPT) for esophageal cancer, organ motion can cause deviations between planned and delivered dose. Owing to posterior beam arrangements, the heart is particularly vulnerable, as the distal fall-off frequently overlaps cardiac tissue. This study quantified heart dose changes during treatment, identified contributing anatomical factors, and evaluated a heart-dose-guided adaptation protocol.MethodsWe retrospectively analyzed 194 esophageal cancer patients treated with IMPT using weekly repeat CT scans (reCTs). Prescriptions were 23 × 1.8 Gy or 28 × 1.8 Gy (RBE). Plans were recalculated on each reCT to derive mean heart dose (MHD) and heart V40Gy. Dose trends were assessed alongside anatomical changes, including diaphragm baseline shift, heart position and volume, heart displacement, internal target volume (ITV), intraesophageal air, posterior subcutaneous adipose tissue, and dysphagia scores. Significant variables were included in an Elastic Net model to predict MHD changes with 10-fold cross-validation. The effect of an adaptation protocol-triggered by MHD increases >1.5 Gy or target underdosage-was evaluated in 111 patients treated after August 2022, 25 of whom underwent replanning due to increasing MHD.ResultsLinear mixed modeling in all reCTs of 194 patients showed significant increases in MHD (0.4 Gy/week, p ConclusionHeart dose increases significantly during IMPT for esophageal cancer due to anatomical changes. Heart-dose-guided adaptive replanning effectively mitigates this increase.