Dosimetric Evaluation of Cardiac Substructures in Irradiation of Esophagus

Abstract

Due to the anatomic proximity of the heart, cardiac toxicity is a major concern in radiation treatment (RT) of esophageal cancer. Historically, the entire heart is considered an organ at risk. However, more recent studies have demonstrated that dose to cardiac substructures may better predict cardiac toxicities. We retrospectively reviewed patients (pts) who had RT to the distal esophagus and evaluated the dose-volume constraints (DVCs) of the cardiac substructures and the whole heart. We hypothesized that the majority of the treatment plans would not meet the DVCs to cardiac substructures noted in the current literature, albeit meeting commonly accepted whole heart DVCs. We identified 27 pts with esophagus or gastroesophageal junction cancer who received RT to the esophagus between January 2017 and December 2022. For each case, the cardiac substructures (4 heart chambers - left/right atrium [L/RA] and left/right ventricle [L/RV], 4 coronary arteries - left common [LCA], left anterior descending [LAD], left circumflex [LCx], and right common [RCA], and great vessels - ascending and descending aorta [A/DA], pulmonary artery [PA], and superior vena cava [SVC]) were contoured based on the contouring atlas developed by Duane et al. DVCs based on existing literature for the whole heart and each cardiac substructure were reviewed and retrospectively analyzed for each treatment plan (Table 1). Eighteen (66.7%) pts received 50 Gy/25 fractions, and nine (33.3%) pts received 50.4 Gy/28 fractions. The dose-volume constraints for the whole heart and each cardiac substructure are shown in Table 1. When considering the heart as a whole organ, all the treatment plans met the V45 and V40 objectives, with a mean V45 of 7.1% and V40 of 10.8%. All the cases also met the constraints for RV and PA. However, none of the cases met the DVCs for RA or LV. Only 6 (22.2%) of cases met the constraint for LCx or AA. We found that despite all the treatment plans meeting the whole heart V45 and V40 constraints, none of the cases met the dose constraints to all cardiac substructures. This suggests that dosimetric evaluation of the whole heart alone may not be sufficient in minimizing cardiac toxicities from RT, and thus further supports the importance of defining the cardiac substructures. Future studies will be needed to standardize the dose constraints to these substructures to ensure patient safety.