ESTRO 2023 - Abstract Book

S530

Sunday 14 May 2023

ESTRO 2023

Patients were split into left and right-sided BC. Left-sided patients were split into gated/non-gated crudely with a cut-off lung volume of 1600 mL (estimated on previous studies). Presence of delineated cardiac structures, including heart and left anterior descending coronary artery (LADCA), was registered. It was assumed, that the presence of a structure implied it being used to guide planning. The original dose distributions were used to score dose to the DL segmented hearts, with these dose metrics: Dmean (MHD), Dmax (D0.027cc), Dmin, V20Gy and V40Gy. Significance was tested using a Mann-Whitney U-test. Results In total 3042 left-and 2764 right-sided BC patients were identified, with a MHD in the cohort of 2.56Gy (± 1.44) and 1.23Gy (± 0.91) respectively. Two centres delineated only LADCA (all left-sided BC) or no cardiac delineations (all right-sided BC), whereas the remaining five centres delineated the whole heart or both heart and LADCA, table 1. Comparing patients treated with or without gating, gated patients showed overall lower heart dose (Dmax: 34.8Gy vs. 46.0Gy, p < 0.01). In gated patients, no significant difference was found between planning with only LADCA or only heart as avoidance structure, with a median heart Dmax at 36.7Gy and 37.2Gy respectively, figure 2. The same tendency was seen in MHD, V20Gy, V40Gy and Dmin. In non-gated patients, significant differences were found between any use of avoidance structures. IMN was delineated in a subgroup of the patients (226/1153) and showed a lower target coverage than for gated patients (CTVn_IMN mean: 39.3Gy vs 47.4Gy, p<0.01), indicating difficulties with meeting the planning objectives. For right-sided BC patients, a higher heart Dmax and MHD was found for patients with no avoidance structures compared to those with heart or both(p<0.05).