目的：本篇研究在探討對於左側乳癌使用強度調控放射治療是否比傳統平行對照正切技術可提供較佳的治療計畫。材料及方法：從2005年1月至2006年12月，共有70位早期左側乳癌病人(Tis-2N0M0)接受乳房保留手術，部分病人也接受了化療。我們針對每個案例同時使用強度調控放射治療及傳統放射治療做電腦計畫，在比較心臟及肺臟的放射劑量、照射體積，和其他劑量分析參數後，再決定選用哪一套治療計畫做實際的臨床治療。結果共有2位病人使用傳統放射治療，68位使用強度調控放射治療。結果：平均順形指數(Conformity indexes)在傳統放射治療及強度調控放射治療分別為1.47及1.08(p<0.05)。強度調控放射治療對於心臟、同側肺臟、對側肺臟的劑量分別可降低38.7%、22.9%、60.9%。急性副作用在可接受範圍內。傳統放射治療有較高的劑量分佈不均勻性(dose heterogeneity)、較大範圍的高劑量區(hot spot)及低劑量區(cold spot)。結論：對於左側乳癌，強度調控放射治療可以降低心臟及兩側肺臟的劑量，也可提供較佳的順形指數(Conformity indexes)和劑量均勻性(dose homogeneity)。但是強度調控放射治療對於照射到周邊的正常組織低劑量區較大。

Background and purpose: To determine whether or not intensity modulated radiation therapy (IMRT) offers a better treatment plan compared with conventional parallel opposed tangential radiation therapy for the left-sided breast cancer patients. Materials and Methods: Between January 2005 and December 2006, we treated 70 patients who had Tis-2N0M0 left-sided breast cancers and underwent breast conservation surgery with or without chemotherapy. Both IMRT and conventional radiotherapy were planned for every patient. After comparing the radiation dose and volume to the heart and lung, and other dosimetric parameters, we then decided which technique to use for individual patient. Conventional radiotherapy was used for 2 patients and IMRT for 68 patients. Results: The mean conformity indexes are 1.47 and 1.08 for conventional radiotherapy and IMRT, respectively (p＜0.05). Radiation dose to the heart, ipsilateral lung, and contralateral lung all can be reduced by 38.7%, 22.9% and 60.9%, respectively, with IMRT. Acute side effects were acceptable. The dose heterogeneity of conventional radiotherapy is greater than IMRT with a large area of cold and hot spots. Conclusions: For the left-sided breast, IMRT can reduce the irradiation dose to the heart and both lungs. It also offers better conformity index and dose homogeneity. However, IMRT delivers very low dose radiation to a larger volume of normal surrounding tissues.