同時雙側乳腺癌(synchronous bilateral breast cancer, SBBC)患者的治療計劃由於複雜的治療體積而面臨挑戰，這使得計劃更加複雜且耗時。為了減少高劑量和低劑量分布在心臟、肺臟正常器官，本研究中提出了一種有效且簡單方式應用於體積弧形調控放射治療計劃(Volumetric modulated arc therapy, VMAT)。五名SBBC 患者參與本研究。在治療計劃中，利用兩個虛擬擋塊(pseudo block)結構來減少整個肺臟和心臟的高劑量體積，並將低劑量區域限制在正常器官中。VMAT 治療計劃由兩個弧形照野組成，處方劑量為45Gy，分為25 次執行。全肺劑量結果顯示，5 名患者的VMAT-B(計劃有兩個虛擬擋塊結構)計劃的平均V5Gy、V10Gy 和V20Gy 分別為34.8±7.2%、23.4±5.0%和14.8±3.0%。VMAT-NB(沒有兩個虛擬擋塊的計劃)，平均V5Gy、V10Gy 和V20Gy 分別為38.6±6.8%、27±5.9%和18.4±4.0%。VMAT-B 和VMAT-NB 計劃的全肺平均劑量分別為8.4±1.4Gy 和9.7±1.6Gy。我們可以觀察到V5Gy、V10Gy、V20Gy 和全肺的平均劑量對於每個劑量參數是具有統計意義的。心臟劑量結果顯示，VMAT-B 計劃中的平均V5Gy、V10Gy、V20Gy 和V30Gy 分別為19.6±3.1%、7.0±2.5%、2.2±1.2%和0.7±0.7%。VMAT-NB 計劃中的平均V5Gy、V10Gy、V20Gy 和V30Gy 為26.2±6.3%、11.3±3.9%、3.9±1.8%和1.5±1.1%。VMAT-B 和VMAT-NB 計劃的心臟平均劑量為4.4±0.5 和5.4±1.0Gy。對於心臟的每個劑量參數具有統計學顯著性。本研究結果顯示，在相似的PTV 具有劑量順形度和均勻度下，VMAT 治療計劃中使用虛擬擋塊明顯可以減少劑量體積及整個肺和心臟的平均劑量。對於其他危急器官(organ at risk, OAR)，它們也被認為是降低器官劑量的有用方法。本研究提出了一種利用VMAT治療計劃中的虛擬擋塊來減少高劑量和低劑量體積的方法，劑量結果表明“Ref-block”虛擬擋塊結構具有潛力降低放射性肺炎和心臟病風險，同時可以保持相同的腫瘤控制率。

Treatment plans for synchronous bilateral breast cancer (SBBC) patients poses a challenge due to complex treatment volumes, it makes the plan more complicated and time consuming. To diminish both high-dose and low-dose volume of heart and lungs, we proposed an efficient and simple strategy for the VMAT (volumetric modulated arc therapy treatment plans) in this study. Five SBBC patients were enrolled for this research. We utilized two pseudo block planning structures to diminish high dose volume of whole lungs and heart, and confined low dose area in normal organs for VMAT plans. Prescription was 45 Gy in 25 fractions to the whole breast. VMAT treatment plan was consist of two partial arcs. In terms of whole lungs, the average V5Gy, V10Gy, and V20Gy in the VMAT-B (plans with two pseudo planning block structures) plan for five patients was 34.8 ± 7.2%, 23.4 ± 5.0%, and 14.8 ± 3.0%. For the VMAT-NB (plans without two pseudo planning block structures) plan, the average V5Gy , V10Gy , and V20Gy was 38.6 ± 6.8% , 27 ± 5.9% , and 18.4 ± 4.0%. The mean dose of whole lungs for VMAT-B and VMAT-NB plans was 8.4 ± 1.4Gy and 9.7 ± 1.6Gy, respectively. We can observe the V5Gy, V10Gy, V20Gy and mean dose of whole lungs were statistically significant for each dosimetric parameter. As for heart, the average V5Gy, V10Gy, V20Gy, and V30Gy in the VMAT-B plan was 19.6 ± 3.1% , 7.0 ± 2.5% , 2.2 ± 1.2% , and 0.7 ± 0.7%. The mean V5Gy, V10Gy, V20Gy, and V30Gy in the VMAT-NB plan was 26.2 ± 6.3 % , 11.3 ± 3.9% , 3.9 ±1.8% , and 1.5 ± 1.1%. The mean dose of heart for VMAT-B and VMAT-NB plan was 4.4 ± 0.5 and 5.4 ± 1.0Gy. There were statistically significant for each dose parameter for the heart. The study demonstrated that pseudo planning structures used in VMAT treatment plans can apparently reduce the dose volume as well as mean dose for whole lungs and heart under the similar PTV conformity and uniformity. For the other OARs, they were also deemed as helpful methods to lower organ dose. We presented an approach to diminish both high-dose and low-dose volume by utilizing some pseudo planning structures in the VMAT treatment plans. The dosimetric results of this research represents that “Ref-block” structures have potential to reduce the risk of radiation pneumonitis and heart disease, while may preserve same tumor control rate.