Abstract
PurposeCardiac effects after breast cancer radiation therapy potentially affect more patients as survival improves. The heart’s heterogeneous radiation exposure and composition of functional structures call for establishing individual relationships between structure dose and specific late effects. However, valid dosimetry requires reliable contouring which is challenging for small volumes based on older, lower-quality computed tomography imaging. We developed a heart atlas for robust heart contouring in retrospective epidemiologic studies.Methods and materialsThe atlas defined the complete heart and geometric surrogate volumes for six cardiac structures: aortic valve, pulmonary valve, all deeper structures combined, myocardium, left anterior myocardium, and right anterior myocardium. We collected treatment planning records from 16 patients from 4 hospitals including dose calculations for 3D conformal tangential field radiation therapy for left-sided breast cancer. Six observers each contoured all patients. We assessed spatial contouring agreement and corresponding dosimetric variability.ResultsContouring agreement for the complete heart was high with a mean Jaccard similarity coefficient (JSC) of 89%, a volume coefficient of variation (CV) of 5.2%, and a mean dose CV of 4.2%. The left (right) anterior myocardium had acceptable agreement with 63% (58%) JSC, 9.8% (11.5%) volume CV, and 11.9% (8.0%) mean dose CV. Dosimetric agreement for the deep structures and aortic valve was good despite higher spatial variation. Low spatial agreement for the pulmonary valve translated to poor dosimetric agreement.ConclusionsFor the purpose of retrospective dosimetry based on older imaging, geometric surrogate volumes for cardiac organs at risk can yield better contouring agreement than anatomical definitions, but retain limitations for small structures like the pulmonary valve.
Highlights
Breast cancer remains the most frequently diagnosed cancer and the leading cause of cancer-related death [1]
Contouring agreement for the complete heart was high with a mean Jaccard similarity coefficient (JSC) of 89%, a volume coefficient of variation (CV) of 5.2%, and a mean dose CV of 4.2%
Dosimetric agreement for the deep structures and aortic valve was good despite higher spatial variation
Summary
Breast cancer remains the most frequently diagnosed cancer and the leading cause of cancer-related death [1]. Aside from potentially cardiotoxic chemotherapy and antiHER2 immunotherapy [4], breast cancer RT can expose the heart to high levels of radiation [5, 6]. The need to address late cardiac effects of breast cancer treatment is widely recognized [4, 7]. Radiation dose to the heart was repeatedly shown to be linked to late cardiac disease [8,9,10,11] with mixed evidence for more recent treatment years [12,13,14]. Radiation therapy-induced late cardiac effects are relevant for patients with Hodgkin lymphoma [15], esophageal cancer [16], and potentially for lung cancer patients [17, 18] with improved survival due to immune-checkpoint inhibitor treatment
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