Cardiac substructure dose distributions in node-positive and node-negative breast cancer patients undergoing 3D-CRT: comparing the predictive accuracy of mean heart dose and mean left ventricular dose.

Abstract

Background and purpose: Cardiotoxicity is a concern, especially in left breast cancer (BC) radiotherapy (RT), and accurate dosimetry is essential for minimizing cardiac exposure. This study evaluated the radiation exposure of cardiac substructures in node-positive and node-negative BC patients who underwent three-dimensional conformal therapy (3D-CRT) and compared the predictive accuracy of mean heart dose (MHD) and mean left ventricular dose (MLVD) in estimating dose distribution to cardiac substructures.

Materials and methods: This study included 55 patients with left-sided breast cancer, comprising 39 with node-positive and 16 with node-negative disease. All underwent adjuvant whole-breast irradiation using 3D-CRT. The heart, ventricles, atria, right coronary (RC), left anterior descending coronary (LADCA), and left circumflex (LCx) arteries were contoured. Dosimetric distributions were evaluated, and Pearson's correlation and linear regression analyses were used to assess the relationship between cardiac substructures.

Results: The distribution of doses to cardiac substructures was heterogeneous, with LADCA receiving the highest doses: 15.6 Gy in node-positive and 13.2 Gy in node-negative breast cancer patients. Linear regression analysis revealed a weak to moderate predictive ability of MHD/MLVD to predict doses received by the cardiac substructure in both groups, with MLVD demonstrating marginally better results. For node-positive patients, the analysis revealed an R² of 0.40 (p < 0.001) for the association between MHD and LADCA and an R² of 0.45 (p < 0.001) for MLVD and LADCA. In node-negative patients, the R² values were 0.27 (p < 0.001) for MHD versus LADCA and 0.30 (p < 0.03) for MLVD versus LADCA. Pearson's correlation analysis for node-positive patients indicated r = 0.63 (p < 0.001) for MHD versus LADCA and r = 0.67 (p < 0.001) for MLVD versus LADCA. For node-negative patients, the correlation coefficients were r = 0.52 (p < 0.001) for MHD versus LADCA and r = 0.54 (p < 0.001) for MLVD versus LADCA.

Conclusion: Radiation exposure to cardiac substructures during 3D-CRT for left breast cancer was heterogeneous, with the LADCA receiving the highest mean dose, followed by the LV. MLVD demonstrated superior predictive accuracy over mean heart dose (MHD) for estimating doses to critical substructures, particularly in node-positive patients.