目的：研究目的是期望在使用阻擋參數設計與優化螺距之螺旋刀放射治療技術於左側乳癌的病症的同時，危急器官劑量比起傳統乳癌對照技術能獲得有效的降低。

材料與方法：本研究是探討左側乳癌患者做螺旋刀治療計劃時參考 An-Cheng Shiau 2014 之限制 阻擋參數設定並搭配優化螺距設定，目的是期望達到較佳的順行度並且降低附近危急器官劑量。 首先，需先得知定位中心位置與實際治療靶體積之位置中軸偏差距離，再參考 Mingli Chen 2011 的表格找到合適的螺距。接著，在設計好完全阻擋圖區與方向性阻擋圖區的計劃套用先前查表得 知的螺距。阻擋圖區的設計仍須考量與靶體積的距離，另外參考 Strydhorst 2011 提出的建議， 需要再繪製虛擬 bolus ，目的是考量到呼吸造成位移的影響。混和式強度調控治療計劃是利用兩 個傳統切線照野射束佔 80% 處方劑量，再加上兩個強度調控射射束當作輔助射束佔 20% 處方劑 量，處方劑量是 50 Gy 分 25 次照射。另外，在肺部器官與心臟劑量，將評估在切線對照之照野 內射束眼內的照野心臟體積與照野肺部體積。

結果：最大照野心臟體積與照野肺部體積分別是15.49 cc 和88.8 cc，相較於混和式強度調控治療 計劃，優化限制性螺旋刀治療計劃可提高靶體積內的最低劑量（39.16±4.958Gy vs. 30.56±9.478 Gy）， 以及提升均勻度指標（HI=PTVm95%-PTVm107%）（0.9888 ± 0.0054 vs. 0.9690 ± 0.0138），順行度指標（Conformity index, CI） （1.5892±0.2998 vs. 1.6286±0.2526）不分軒輊。 另外，優化限制性螺旋刀治療計劃，比起傳統混和式強度調控治療計劃，在心臟的平均劑量是降 低了 18.38%（2.72 ± 2.214 Gy vs. 2.22 ± 1.872 Gy）；在左肺部的平均劑量降低了 13.74%（5.75 ± 0.848 Gy vs. 4.96 ± 1.352 Gy）。

結論：優化限制性螺旋刀治療技術，在心臟與肺部器官呈現的劑量是較低的，這是因為此技術在計劃過程中有更多可調整的空間。相信螺旋刀治療技術的研究，在左側乳癌放射治療是有幫助的。

Purpose : In order to reduce heart and ipsilateral lung dose, a modified TomoTherapy planning technique for left-sided breast was introduced and compared to Hybrid-IMRT technique.

Materials and Methods : A modified TomoTherapy planning technique was designed for left-sided breast cancer patients. It was based on the Limited-TomoTherapy planning technique but applying optimal pitches to achieve better conformity and lower heart and ipsilateral lung dose. First, the optimized off-axis distance was determined. Then the optimal pitches were chosen according to the optimized off-axis distance. The last step was applying optimal pitches with the Limited- TomoTherapy planning technique, which employed several artificial contours such as the Completeblock, Directional-block for near PTV area and the virtual bolus, in the optimized process of the leftsided breast TomoTherpy planning. Hybrid-IMRT plans were designed by tangential-fields and IMRT fields combined. The prescription dose was 50 Gy in 25 fractions to PTV. The lung and heart dose volume were measured and analyzed in Beam’s-eye-view of tangential-fields with in-field heart volume and in-field lung volume.

Result : The maximum volumes of in-field heart volume and in-field lung volume were 15.49 cc and 88.8 cc, respectively. Comparing to the Hybrid-IMRT technique, the modified TomoTherapy planning technique increased the minimal dose of PTV (39.16±4.958 Gy vs. 30.56±9.478 Gy), the homogeneity index (HI= PTVm95%-PTVm107%) was better (0.9888 ± 0.0054 vs. 0.9690 ± 0.0138) and conformity index (CI= V95%/PTV95% ) was no obvious difference (1.5892±0.2998 vs. 1.6286±0.2526). The Dmean of heart in modified planning technique was under 18.38% than in the Hybrid-IMRT technique (2.22 ± 1.872 Gy vs. 2.72 ± 2.214 Gy). The Dmean of Lt lung was under 13.74% in modified planning technique than in the Hybrid-IMRT technique (4.96 ± 1.352 Gy vs. 5.75 ± 0.848 Gy).

Discussion and Conclusions : The modified planning technique showed better dose reduction in heart and lung, due to its more flexibility in the optimized planning process. It should be useful in left-sided breast treatment with TomoTherapy.