Background:Prone breast radiotherapy has been shown to optimally spare the dose to the heart and lungs; we report on the heart and left anterior descending coronary artery (LAD) dosimetry and their implications for current care.Aims: (I) To measure the mean heart dose (MHD) and LAD mean and maximum doses (Dmean and Dmax) in patients with left-side breast cancer who have undergone hypo-fractionated whole breast radiotherapy (WBRT) with a concomitant boost to the post-operative cavity (40.50 Gy to the breast and 48 Gy to the cavity in 15 fractions) in the prone position; (II) to compare the dosimetry results to those reported in the literature for other techniques.Materials and Methods:In a consecutive series of 524 irradiated left-side breast cancer patients, heart and LAD dosimetry data were collected and correlated to breast volume and the volume of the radiation boost to the tumor cavity. A descriptive statistical analysis was performed to compare the same dosimetry data with those reported in the literature from supine techniques. To account for dosimetry differences in hypo-fractionation and conventional fractionated regimens (50–60 Gy in 25–30 fractions) reported in the literature, the cardiac doses were converted to the equivalent dose in 2 Gy fractions (EQD2). As previously reported, the prone setup protocol placed the medial edges of the tangential radiation fields at least 2.5 mm from the contoured LAD.Results:In all patients’ plans, the target coverage was successfully achieved. The mean values (±SD) were as follows: MHD = 0.69 Gy (±0.19) (EQD2 0.35 Gy ± 0.1); LAD Dmean = 2.20 Gy (±0.68) (EQD2 1.18 Gy ± 0.35); LAD Dmax = 4.44 Gy (±1.82) (EQD2 2.55 Gy ± 0.97). The values were consistently lower compared with those achieved by the multiple supine techniques reported in the literature. Spearman’s correlation analysis revealed a strong positive correlation between LAD and heart dosimetry variables. In contrast, no strong correlation was observed between the cardiac dose metrics and breast volume, boost volume, or their ratio index. A linear correlation was detected between LAD Dmean and LAD D2% (R20.64); LAD D2% and heart D2% (R20.60); LAD Dmax and heart D2% (R20.41).Conclusions:The prone position protocol minimizes heart and LAD exposure. This approach results in a dosimetry advantage when compared with more complex and expensive WBRT techniques in the supine position.
背景：俯卧位乳腺放疗已被证实能最大限度地减少心脏和肺部的受照剂量；本研究旨在报告心脏及左前降支冠状动脉（LAD）的剂量学数据，并探讨其对当前临床实践的指导意义。 目的：（I）测量左侧乳腺癌患者在俯卧位下接受大分割全乳放疗（WBRT）联合瘤床同步推量照射（全乳40.50 Gy，瘤床48 Gy，分15次完成）后的平均心脏剂量（MHD）及LAD平均剂量与最大剂量（Dmean与Dmax）；（II）将剂量学结果与文献报道的其他技术进行比较。 材料与方法：连续纳入524例接受放疗的左侧乳腺癌患者，收集其心脏及LAD剂量学数据，并与乳腺体积及瘤床推量照射体积进行相关性分析。通过描述性统计学方法将本研究的剂量学数据与文献报道的仰卧位技术数据进行对比。为统一文献中大分割方案（15次）与传统分割方案（25-30次，50-60 Gy）的剂量学差异，心脏剂量均转换为2 Gy分次等效剂量（EQD2）。根据既往报道的俯卧位定位方案，切线野内缘与勾画的LAD距离至少保持2.5 mm。 结果：所有患者的计划均成功实现靶区覆盖。剂量学平均值（±标准差）如下：MHD=0.69 Gy（±0.19）（EQD2 0.35 Gy±0.1）；LAD Dmean=2.20 Gy（±0.68）（EQD2 1.18 Gy±0.35）；LAD Dmax=4.44 Gy（±1.82）（EQD2 2.55 Gy±0.97）。与文献报道的多种仰卧位技术相比，本研究剂量值持续处于更低水平。Spearman相关性分析显示LAD与心脏剂量学参数间存在强正相关性。而心脏剂量指标与乳腺体积、推量体积及其比值指数均未呈现强相关性。LAD Dmean与LAD D2%（R²=0.64）、LAD D2%与心脏D2%（R²=0.60）、LAD Dmax与心脏D2%（R²=0.41）之间存在线性相关。 结论：俯卧位方案能显著降低心脏及LAD的受照剂量。与仰卧位下更复杂且昂贵的WBRT技术相比，该方案具有明确的剂量学优势。
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