目的：回溯性分析左側乳癌病人接受乳房保留手術後放射治療心臟和左冠狀動脈前降支的照射 劑量及探討降低其照射劑量的可能性。 材料與方法：本研究篩選21 名接受放射治療之左側乳癌患者，其中 14 名接受乳房相切照野放 射治療，7 名接受乳房相切照野放射治療及鎖骨上窩強度調控放射治療。所有病人的心臟和左 冠狀動脈前降支的接受劑量都以劑量- 體積圖（dose-volume histogram, DVH）作分析，以皮爾 遜積差相關係數評估心臟和冠狀動脈前降支接受劑量的相關性，以 t-test 評估鎖骨上窩強度調控 放射治療治療與否對於心臟和冠狀動脈前降支接受劑量是否有顯著的差異。 結果：整體患者的心臟平均接受劑量為 4.04 Gy（範圍為 1.75-11.15 Gy），左冠狀動脈前降支 的平均接受劑量為 21.29 Gy（範圍為 6.99-35.28 Gy），平均最大接受劑量為 54.31 Gy（範圍為 50.55-58.42 Gy），心臟平均接受劑量和左冠狀動脈前降支平均劑量有高度的關聯性（r= 0.80, p< 0.01）；左冠狀動脈前降支平均劑量和在照野內之體積有高度關聯性（r= 0.94, p< 0.0001），有 7 名患者同時接受乳房相切照野放射治療及鎖骨上窩強度調控放射治療，心臟平均接受劑量為 4.15 Gy（範圍為 2.58-8.9 Gy），左冠狀動脈前降支的平均接受劑量為 22.08 Gy（範圍為 16.57- 35.28 Gy），平均最大接受劑量為 55.71 Gy（範圍為 52.99-58.42 Gy）；相切照野放射治療對左冠 狀動脈前降支的平均接受劑量為 21.93 Gy（範圍為16.49-35.21 Gy），鎖骨上窩強度調控放射治 療對左冠狀動脈前降支的平均接受劑量為 0.15 Gy（範圍為 0.05-0.35 Gy），相切照野放射治療 有無鎖骨上窩強度調控放射治療對於心臟及左冠狀動脈前降支的平均接受劑量無明顯差異。 結論：對於接受接受左側乳房相切照野放射治療的病人，左冠狀動脈前降支接受劑量和照野內 之體積有高度正相關；心臟平均劑量和左冠狀動脈前降支的平均接受劑量有高度的相關性，而 且左冠狀動脈在電腦斷層不一定有良好之顯像，因此我們建議做治療計劃時，若是病人的左冠 狀動脈在電腦斷層上難以辨認，可以限制心臟平均接受之劑量，以達到降低左冠狀動脈劑量的 目的。

Purpose : The aim of this retrospective study is to quantify dose irradiated to the heart and the left anterior descending coronary artery (LADCA) in left breast cancer patients treated with adjuvant breast radiotherapy and analyse the probable causes of high dose to the heart and LADCA. Methods and Materials : Twenty-one consecutive patients with left-sided breast cancer who underwent adjuvant radiotherapy to the breast between August 2012 and October 2013 are enrolled in our study. All patients were irradiated with 6- or 10-MV tangential beams to the breast and seven patients of them also received supraclavicular fossa (SCF) irradiation with IMRT technique. For each dose plan, dose–volume histograms (DVHs) for the heart and LADCA were calculated and analyzed. Pearson correlation coefficient was calculated to assess the relationship between average heart Dmean (mean dose), LAD Dmean and LADmax (maximum dose) and between LAD Dmean and volume of LADCA in the radiation fields (i.e., it received >25 Gy). Student's t test was used to assess the statistical significance of differences in radiation dose to LADCA and heart between patients who received SCF IMRT or not. Results : For the 21 patients given left breast irradiation, the average mean [range] dose was 4.04 [1.75-11.15] Gy to the heart and 21.29 [6.99-35.28] Gy to the LADCA, and the average maximum dose was 54.31 [50.55-58.42] Gy to the LADCA. There is significant correlation between Dmean to the heart and LADCA (r= 0.80, p < 0.01). The Dmean to LADCA was postulated to increase 3.44 Gy for each increase of 1 Gy in the mean radiation dose delivered to the heart in our study. There is significant correlation between Dmean to LADCA and the volume of LAD in the radiation fields (i.e., it received >25 Gy) (r= 0.94, p< 0.0001). The Dmean to LADCA was postulated to increase 0.77 Gy for each increase of 1 ml of LADCA volume in the radiation field. For 7 patients who received left-tangential radiotherapy and SCF IMRT, the average mean dose was 4.15 [2.58-8.9] Gy to the heart and 21.93 [16.49-35.21] Gy to the LADCA, and the average maximum dose was 55.21 [52.63-57.79] Gy to the LADCA. SCF IMRT contributed to average mean dose 0.15 [0.05-0.35] Gy and average maximum dose 0.43 [0.15-0.68] Gy to the LADCA. There is no significant difference in Dmean to the LADCA and heart between patients who received SCF IMRT or not (p= 0.38, p= 0.45, respectively).There is significant correlation between Dmean to the heart and LADCA. The patients with the higher mean heart dose had the higher mean LADCA dose. We may suggest to limit mean dose to LADCA by avoiding volume of LADCA in the treatment fields if well visualized LADCA on CT scan or limiting the mean heart dose to lower mean LADCA dose if poor visualization of LADCA on CT scan.