目的：測量以等中心點相切照野技術治療乳癌患者時之對側乳房劑量.並觀察添加鉛皮及橡皮材 質壤充物的屏蔽效果，及評估寰際治療時之可行性。材料與方法：利用不對稱照野(asymmetric jaws)採三個照野的等中心點相切照野技術(mono-isocenter-tangential technipue)，以兩個相切照野(tangential fields)來治療乳房、胸腔壁、內乳淋巴結及腋下淋巴結，再結合一個上鎖骨照野(supraclavcularfield)來治療鎖骨上淋巴結。共有11名屬於三至四期乳癌並已做過乳房切除手術的乳癌患者接受乳房劑量評估，其年齡從40-51歲(平均46歲)。我們在其對側乳房貼上熱發光劑量計(TLO).於每次治療時分別添加不同厚度的鉛沒及橡皮材質填充物予以屏蔽，治療後讀欺TLO值。結果：在單次治療給予180 cCy.未添加任何屏蔽時.對側乳房平均接受11±1.9 cGy的劑量。在添加0.5cm、1 cm、1.5cm、2 cm壙充物後，對側乳房的劑量分別減少為4.6±0.5cGy、3.2±0.3 cGy、3.0±0.2 cGy及2.8±0.l cGy；而在添加0.3 cm及0.5 cm鉛皮後，對側乳房劑量分別減為2.7±0.2 cGy及2.6±0.2 cGy。因此，在治療28次總劑量達5040 cGy後，估計對側乳房將接受約332 cGy的散射劑量；在添加2 cm的填充物及0.5 cm的鉛皮屏蔽後，可使對側乳房表面劑量分別減少為80cGy及73cGy，減少約75％的散射劑量。結論：橡皮材質壙充物在放射治療上一般被應用於提昇身體淺部劑量，由本研究得知，其同時可用以降低治療乳癌時之對側乳房劑量。由於壤充物在各放射治療部門皆易購得或容易製作，且易於固定及緊貼於患者身上.因此值得加以運用以減少病患之散射劑量。

　　　　　Purpose: To measure the doses of contralaterai breast from mono-isocenter tangential fields. To investigate the shielding effect of lead sheetand rubber bolus and evaluate the availability on practical treatment.Materials and Methods: We develop mono-isocenter tangential technique. Twotangential fields was applied to treat patient's breast, chest wall,internal mammary chain and axillary lymph nodes. The supraciavicular lymphnodes were treated with a supraciavicular field. 11 stage Ill, IV post-mastectomy patients were enrolled in our study. TLDs were placed on theircontralateral breast for dosage evaluation with the following condition: (1)without rubber bolus or lead sheet, (2) with lead sheet, (3) with rubberbolus. The prescribe dose was 180 cGy daily.Results: We found that the to contralateral breast was 1 1 ±1.9 cGy daily,when there is no shielding. By adding 0.5 cm, 1 cm, 1.5 cm and 2 cm bolus oncontralateral breast, the doses decreased to 4.6 ±0.5 cGy, 3.2 ±0.3 cGy,3.0 ±0.2 cGy and 2.8 ±0.1 cGy, respectively While 0.3 cm and 0.5 cm leadsheet were added, the doses decreased to 2.7 ±0.2 cGy and 2.6 ±0.2 cGy,respectively. Therefore, while the total dose reach 5040 cGy, the dose tocontralaterai breast was estimated as 332 cGy. Adding a 2 cm boius or 0.5 cmlead sheet will effectively reduce the dose to 80 cGy and 73 cGy,respectiveiy, which eliminate approximately 75% scatter radiation doses.Conclusion: Rubber boius is usually used for increasing body surface doseduring radiation therapy. This study indicated that rubber boius candecrease the doses to contralateral breast when a tangential field techniqueis applied. Rubber bolus is a material which can be easily available, andproved to effectively reduce the dose of contralateral breast, it is also easyto fix on patient's chest wall, so we encourage the usage of bolus duringradiation therapy for breast cancer.