Background and purposeThe heart is a complex anatomical organ and contouring the cardiac substructures is challenging. This study presents a reproducible method for contouring left ventricular and coronary arterial segments on radiotherapy CT-planning scans.Material and methodsSegments were defined from cardiology models and agreed by two cardiologists. Reference atlas contours were delineated and written guidelines prepared. Six radiation oncologists tested the atlas. Spatial variation was assessed using the DICE similarity coefficient (DSC) and the directed Hausdorff average distance (d→H,avg). The effect of spatial variation on doses was assessed using six different breast cancer regimens.ResultsThe atlas enabled contouring of 15 cardiac segments. Inter-observer contour overlap (mean DSC) was 0.60–0.73 for five left ventricular segments and 0.10–0.53 for ten coronary arterial segments. Inter-observer contour separation (mean d→H,avg) was 1.5–2.2 mm for left ventricular segments and 1.3–5.1 mm for coronary artery segments. This spatial variation resulted in <1 Gy dose variation for most regimens and segments, but 1.2–21.8 Gy variation for segments close to a field edge.ConclusionsThis cardiac atlas enables reproducible contouring of segments of the left ventricle and main coronary arteries to facilitate future studies relating cardiac radiation doses to clinical outcomes.

During the past decade planning of adjuvant radiotherapy (RT) of early breast cancer has changed from two-dimensional (2D) to 3D conformal techniques. In the planning computerised tomography (CT) scan both the targets for RT and the organs at risk (OARs) are visualised, enabling an increased focus on target dose coverage and homogeneity with only minimal dose to the OARs. To ensure uniform RT in the national prospective trials of the Danish Breast Cancer Cooperative Group (DBCG), a national consensus for the delineation of clinical target volumes (CTVs) and OARs was required. Material and methods. A CT scan of a breast cancer patient after surgical breast conservation and axillary lymph node (LN) dissection was used for delineation. During multiple dummy-runs seven experienced radiation oncologists contoured all CTVs and OARs of interest in adjuvant breast RT. Two meetings were held in the DBCG Radiotherapy Committee to discuss the contouring and to approve a fi nal consensus. The Dice similarity coeffi cient (DSC) was used to evaluate the delineation agreement before and after the consensus. Results. The consensus delineations of CTVs and OARs are available online and a table is presented with a contouring description of the individual volumes. The consensus provides recommendations for target delineation in a standard patient both in case of breast conservation or mastectomy. Before the consensus, the average value of the DSC was modest for most volumes, but high for the breast CTV and the heart. After the consensus, the DSC increased for all volumes. Conclusion. The DBCG has provided the fi rst national guidelines and a contouring atlas of CTVs and OARs defi nition for RT of early breast cancer. The DSC is a useful tool in quantifying the effect of the introduction of guidelines indicating improved inter-delineator agreement. This consensus will be used by the DBCG in our prospective trials.

Purpose Incidental cardiac irradiation can cause cardiac injury, but little is known about the effect of radiation on specific cardiac segments. Methods For 456 women who received breast cancer radiotherapy between 1958 and 2001 and then later experienced a major coronary event, information was obtained on the radiotherapy regimen they received and on the location of their cardiac injury. For 414 women, all with documented location of left ventricular (LV) injury, doses to five LV segments were estimated. For 133 women, all with documented location of coronary artery disease with ≥ 70% stenosis, doses to six coronary artery segments were estimated. For each segment, numbers of women with left-sided and right-sided breast cancer were compared. Results Of women with LV injury, 243 had left-sided breast cancer and 171 had right-sided breast cancer (ratio of left v right, 1.42; 95% CI, 1.17 to 1.73), reflecting the higher typical LV radiation doses in left-sided cancer (average dose left-sided, 8.3 Gy; average dose right-sided, 0.6 Gy; left minus right dose difference, 7.7 Gy). For individual LV segments, the ratios of women with left- versus right-sided radiotherapy were as follows: inferior, 0.94 (95% CI, 0.70 to 1.25); lateral, 1.42 (95% CI, 1.04 to 1.95); septal, 2.09 (95% CI, 1.37 to 3.19); anterior, 1.85 (95% CI, 1.39 to 2.46); and apex, 4.64 (95% CI, 2.42 to 8.90); corresponding left-minus-right dose differences for these segments were 2.7, 4.9, 7.2, 10.4, and 21.6 Gy, respectively ( P < .001). For women with coronary artery disease, the ratios of women with left- versus right-radiotherapy for individual coronary artery segments were as follows: right coronary artery proximal, 0.48 (95% CI, 0.26 to 0.91); right coronary artery mid or distal, 1.69 (95% CI, 0.85 to 3.36); circumflex proximal, 1.46 (95% CI, 0.72 to 2.96); circumflex distal, 1.11 (95% CI, 0.45 to 2.73); left anterior descending proximal, 1.89 (95% CI, 1.07 to 3.34); and left anterior descending mid or distal, 2.33 (95% CI, 1.19 to 4.59); corresponding left-minus-right dose differences for these segements were -5.0, -2.5, 1.6, 3.5, 9.5, and 38.8 Gy ( P = .002). Conclusion For individual LV and coronary artery segments, higher radiation doses were strongly associated with more frequent injury, suggesting that all segments are sensitive to radiation and that doses to all segments should be minimized.