Development of delineation for the left anterior descending coronary artery region in left breast cancer radiotherapy: An optimized organ at risk

Background and purpose: The left anterior descending coronary artery (LAD) and diagonal branches (DBs) are blurred on computed tomography (CT). We aimed to define the LAD region (LADR) with adequate inclusion of the LAD and DBs and contouring consistency.

Methods and materials: The LADR was defined using coronary CT angiograms. The inclusion ratio was used to assess the LAD and DBs inclusion by the LADR. Four radiation oncologists delineated the LAD and LADR, using contrast-enhanced CT of 15 patients undergoing left breast radiotherapy. The Sørensen-Dice similarity index (DSI), Jaccard similarity index (JSI), and Hausdorff distance (HD) were calculated to assess similarity. The mean dose (D_mean) and maximum dose (D_max) to the LAD and LADR were calculated to compare consistency. Correlations were evaluated using Pearson's correlation coefficient.

Results: The inclusion ratio of the LAD by the LADR was 96%. The mean DSI, JSI, and HD values were respectively 27.9%, 16.7%, and 0.42mm for the LAD, and 83.1%, 73.0%, and 0.18mm for the LADR. The D_mean between the LAD and LADR were strongly correlated (r=0.93).

Conclusion: Delineation of the LADR significantly improved contouring similarity and consistency for dose reporting. This could optimize dose estimation for breast radiotherapy.