Key result
In women irradiated for breast cancer using 2-dimensional planning, cardiac segment doses were highly correlated and interpatient dose variation was substantial near field borders (3-47 Gy).
Why the study?
To evaluate whether cardiac segment doses estimated from typical CT scans in women treated with 2-dimensional radiation therapy planning are accurate enough for use in dose-response relationships.
Observational (n=470)
In women treated with historical 2D radiation therapy for breast cancer, cardiac segment doses are highly correlated, limiting the ability to develop quantitative segment-specific dose-response relationships, though they can be used to rank segments by relative dose.
Segment dose estimates from 2D charts show limited utility for quantitative dose-response due to correlations and uncertainties; leaves open need for modern validation.
PURPOSE: Incidental cardiac exposure during radiation therapy may cause heart disease. Dose-response relationships for cardiac structures (segments) may show which ones are most sensitive to radiation. Radiation-related cardiac injury can take years to develop; thus, studies need to involve women treated using 2-dimensional planning, with segment doses estimated using a typical computed tomography (CT) scan. We assessed whether such segment doses are accurate enough to use in dose-response relationships using the radiation therapy charts of women with known segment injury. We estimated interregimen and interpatient segment dose variability and segment dose correlations. METHODS AND MATERIALS: The radiation therapy charts of 470 women with cardiac segment injury after breast cancer radiation therapy were examined, and 41 regimens were identified. Regimens were reconstructed on a typical CT scan. Doses were estimated for 5 left ventricle (LV) and 10 coronary artery segments. Correlations between cardiac segments were estimated. Interpatient dose variation was assessed in 10 randomly selected CT scans for left regimens and in 5 for right regimens. RESULTS: For the typical CT scan, interregimen segment dose variation was substantial (range, LV segments <1-39 Gy; coronary artery segments <1-48 Gy). In 10 CT scans, interpatient segment dose variation was higher for segments near field borders (range, 3-47 Gy) than other segments (range, <2 Gy). Doses to different left-anterior descending coronary artery (LADCA) segments were highly correlated with each other, as were doses to different LV segments. Also, LADCA segment doses were highly correlated with doses to LV segments usually supplied by the LADCA. For individual regimens there was consistency in hotspot location and segment ranking of higher-versus-lower dose. CONCLUSIONS: The scope for developing quantitative cardiac segment dose-response relationships in patients who had 2-dimensional planning is limited because different segment doses are often highly correlated, and segment-specific dose uncertainties are not independent of each other. However, segment-specific doses may be reliably used to rank segments according to higher-versus-lower doses.
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Duane et al. (2019) conducted an observational in Cardiac segment injury after breast cancer radiation therapy (n=470). 2-dimensional radiation therapy for breast cancer was evaluated on Interregimen and interpatient segment dose variability and segment dose correlations. In women irradiated for breast cancer using 2-dimensional planning, cardiac segment doses were highly correlated and interpatient dose variation was substantial near field borders (3-47 Gy).
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