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据报道,乳腺癌在全球女性恶性肿瘤中的发病率位居第一[1]。放疗可提高乳腺癌患者的术后生存率,降低其局部复发率[2-4]。由于乳腺癌患者预后生存期相对较长,因此减少放疗对心脏和肺等危及器官的不良作用非常重要[5]。目前,越来越多的左侧乳腺癌术后患者采用深吸气屏气(deep inspiration breath-hold,DIBH)放疗,此方法可有效降低心脏等器官的受照剂量[6],但是DIBH技术仅在患者屏气间期直线加速器出束治疗,比传统治疗延长了治疗时间。乳腺癌改良根治术后放疗靶区形状极不规则,容积旋转调强放疗(volumetric modulated arc therapy, VMAT)对复杂靶区更具优势,采用DIBH结合VMAT技术不仅能提高靶区剂量分布,还可显著降低患者正常组织的受照剂量[7-8]。
非均整器(flattening filter free,FFF)模式是一种新型的高剂量率技术,其可明显降低机头散射,缩短放疗照射时间,提高治疗效率[9-10]。直线加速器中加均整器(flattening filter,FF)的作用是为了使靶区内剂量分布均匀,在调强技术未成熟之前,FF对于靶区剂量分布非常重要,随着调强放疗和VMAT的普及,直线加速器均能通过多叶准直器的运动实现靶区内剂量的均匀分布,理论上完全可以移除FF[11]。与FF模式相比较,FFF的射线质变软,剂量率增加,辐射野外散射减少,可降低正常组织的受照剂量,从而降低二次致癌的发生概率[12]。
本研究将多项新技术进行整合,在左侧乳腺癌改良根治术后DIBH放疗中,比较FFF和FF模式下 VMAT计划的剂量学特性以及机器的执行效率,为临床治疗提供一定的参考。
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16例乳腺癌改良根治术后患者2种计划均满足95%以上的靶区体积达到处方剂量50 Gy,其中1例患者2种计划的DVH和等剂量曲线分布对比如图1和图2所示,结果显示2种计划的靶区剂量分布相似,但FFF模式下危及器官的受照剂量明显低于FF模式。
图 1 左侧乳腺癌改良根治术后患者(女性,46岁)2种容积旋转调强技术计划靶区及危及器官的剂量体积直方图
Figure 1. Dose volume histogram comparison of the two volumetric modulated arc therapy plans in a patient (female, 46 years old) with left breast cancer after modified radical mastectomy
图 2 左侧乳腺癌改良根治术后患者(女性,46岁)2种容积旋转调强放疗计划同一CT图像等剂量线分布比较 A为FFF-VMAT计划;B为FF-VMAT计划。A和B图从左至右依次为横断面、冠状面、矢状面图。FFF为非均整器;VMAT为容积旋转调强放疗;FF为均整器
Figure 2. Comparison of isodose distribution in the same CT images with two volumetric modulated arc therapy plans of a patient (female, 46 years old) with left breast cancer after modified radical mastectomy
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由表1可知,2种计划的6个靶区剂量学参数D2%、D50%、D98%、CI、 HI、GI均相近,且差异均无统计学意义(均P>0.05);FFF模式机器的总跳数明显高于 FF模式,且为FF模式的1.32倍,差异有统计学意义(P<0.05);但 FFF 模式的执行时间为FF的88.9%,且二者间的差异有统计学意义(P<0.05)。
参数 FFF-VMAT FF-VMAT t值 P值 D2%(cGy) 5640.22±70.09 5613.52±63.07 1.644 0.121 D50%(cGy) 5323.74±48.55 5307.29±51.74 1.462 0.164 D98%(cGy) 4881.38±32.21 4891.64±31.88 −1.386 0.186 适形指数 0.87±0.49 0.87±0.05 −0.490 0.631 均匀指数 0.14±0.02 0.14±0.01 1.415 0.178 梯度指数 3.24±0.66 3.30±0.67 −1.519 0.150 机器跳数(MU) 1073.41±143.79 815.70±87.69 8.665 <0.001 执行时间(s) 128.00±11.64 144.75±11.45 −4.373 0.001 注:FFF为非均整器;VMAT为容积旋转调强放疗;FF为均整器;Dx%表示x%靶体积的受照剂量 表 1 16例左侧乳腺癌改良根治术后女性患者2种VMAT计 划的靶区剂量及机器参数比较(
)$ \bar{{x}}\pm {s} $ Table 1. Comparison of target dosimetric and machine parameters between the two volumetric modulated arc therapy plans in 16 female patients with left breast cancer after modified radical mastectomy (
)$ \bar{{x}}\pm {s} $ -
2种计划的危及器官受照剂量如表2所示。由表2可知,FFF模式下,心脏受照剂量的V5 Gy、V30 Gy及Dmean,患侧肺V5 Gy、V10 Gy及Dmean,全肺V5 Gy、V10 Gy、V20 Gy及Dmean,患者受照剂量的V5 Gy均低于FF模式,组间比较差异均有统计学意义(均P<0.05);虽然患侧肺V20 Gy,健侧肺Dmean、V5 Gy,健侧乳腺 Dmean,脊髓危及器官计划体积的Dmean、Dmax,均略低于 FF 模式,但其差异均无统计学意义(均P>0.05)。
参数 FFF-VMAT FF-VMAT t值 P值 心脏 V5 Gy(%) 32.19±7.18 34.27±7.29 −2.156 0.048 V30 Gy(%) 1.33±1.07 1.70±1.27 −2.632 0.019 Dmean(cGy) 508.50±84.96 587.43±126.48 −2.689 0.017 左肺(患侧肺) V5 Gy(%) 52.02±3.80 55.82±3.55 −4.741 <0.001 V10 Gy(%) 37.80±5.53 40.65±4.23 −2.494 0.025 V20 Gy(%) 27.45±4.82 29.19±3.94 −2.058 0.057 Dmean(cGy) 1418.31±136.02 1516.83±171.71 −2.467 0.026 右肺(健侧肺) V5 Gy(%) 12.83±2.57 13.59±3.04 −0.986 0.340 Dmean(cGy) 278.43±57.28 294.51±44.58 −0.908 0.378 全肺 V5 Gy(%) 34.88±3.14 36.96±3.92 −2.156 0.048 V10 Gy(%) 21.23±3.44 22.87±3.92 −2.320 0.035 V20 Gy(%) 12.55±1.93 13.71±1.61 −2.600 0.020 Dmean(cGy) 829.55±63.94 919.68±59.36 −3.928 0.001 右乳腺(健侧) V5 Gy(%) 23.41±4.06 23.41±3.99 0.001 0.999 Dmean(cGy) 425.96±88.41 435.89±92.34 −0.830 0.420 脊髓外放0.5 cm Dmax(cGy) 2677.70±471.84 2681.10±506.08 −0.064 0.950 Dmean(cGy) 627.55±159.14 610.19±162.16 1.184 0.255 患者受照剂量 V5 Gy(%) 25.71±3.74 27.48±3.74 −2.465 0.026 注:FFF为非均整器;VMAT为容积旋转调强放疗;FF为均整器;Vx Gy为≥x Gy体积占总体积的百分比;Dmean为平均剂量;Dmax为最大剂量 表 2 16例左侧乳腺癌改良根治术后女性患者2种VMAT计 划的危及器官剂量学比较(
)$ \bar{{x}}\pm {s} $ Table 2. Comparison of dosimetry of organs at risk of two volumetric modulated arc therapy plans in 16 female patients with left breast cancer after modified radical mastectomy (
)$ \bar{{x}}\pm {s} $
非均整器模式在左侧乳腺癌改良根治术后患者深吸气屏气容积旋转调强放疗中的剂量学优势
Dosimetric advantages of flattening filter free technique in deep inspiration breath-hold treatments of left-sided breast cancer after modified radical mastectomy with volumetric modulated arc therapy
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摘要:
目的 比较非均整器(FFF)模式和均整器(FF)模式在左侧乳腺癌改良根治术后深吸气屏气(DIBH)动态容积旋转调强放疗(VMAT)中的剂量学差异。 方法 回顾性分析2020年12月至2021年5月在西安交通大学第一附属医院行DIBH放疗的16例左侧乳腺癌改良根治术后女性患者的临床资料,年龄37~61(43.5±5.7)岁。对同一患者分别设计FFF和FF模式的VMAT计划,给予计划靶区(PTV)相同的处方剂量50 Gy/25次,在达到相同的剂量归一条件下,比较靶区剂量学、危及器官受量及机器执行效率的差异。组间数据比较采用配对t检验。 结果 2种模式下靶区PTV的D2%、D50%、D98%(Dx%表示x%靶体积的受照剂量)、适形指数、平均指数及梯度指数差异均无统计学意义(t=−1.519~1.644,均P>0.05);FFF模式的心脏V5 Gy、V30 Gy(Vx Gy表示≥x Gy体积占总体积的百分比)及平均剂量(Dmean),患侧肺V5 Gy、V10 Gy及Dmean,全肺V5 Gy、V10 Gy、V20 Gy及Dmean,患者受照剂量的V5 Gy均优于FF模式,组间比较差异均有统计学意义(t=−4.741~−2.156,均P<0.05);FFF模式机器跳数是FF模式的1.32倍[(1073.41±143.79)MU对(815.70±87.69) MU],但执行时间却减少为FF模式的88.9%[(128.00±11.64) s对(144.75±11.45) s],且差异均有统计学意义(t=8.665、−4.373,均P<0.05)。 结论 2种模式下靶区剂量相似,FFF模式危及器官受照剂量更低,并且可显著缩短DIBH治疗时间。 Abstract:Objective To compare the dosimetry difference between flattening filter free (FFF) mode and flattening filter (FF) mode in deep inspiration breath-hold(DIBH) treatments of left-sided breast cancer after modified radical mastectomy with volumetric modulated arc therapy (VMAT). Methods Retrospectively analyzed the clinical data of 16 female patients with left breast cancer after modified radical mastectomy with DIBH radiotherapy in the First Affiliated Hospital of Xi'an Jiaotong University from December 2020 to May 2021, aged 37 to 61 (43.5±5.7) years old. VMAT plans of FFF and FF modes were designed for the same patient, and the same prescription dose of 50 Gy/25 times was set in the planning target volume (PTV). Under the same dose normalization, the dosimetric parameters of the target and the organs at risk(OAR) and treatment efficiency were compared between the two plans. Paired t-test was used to compare the data between groups. Results No significant differences in D2%, D50%, D98%, CI , HI and GI were found in the target area between the two modes (t=−1.519-1.644; all P>0.05). FFF mode was superior to FF mode in protection of OAR, such as V5 Gy, V30 Gy (Vx Gy: ≥x Gy volume as a percentage of total volume) and mean dose (Dmean) of heart; V5 Gy, V10 Gy and Dmean of ipsilateral lung; V5 Gy, V10 Gy, V20 Gy and Dmean of whole lung; and V5 Gy of patient dose, and the differences between the two modes were statistically significant (t=−4.741 to−2.156; all P<0.05). The total monitor units of FFF mode was 1.32 times of that in FF mode ((1073.41±143.79) MU vs.(815.70±87.69) MU), but the total delivery time was reduced to 88.9% of that in FF mode((128.00±11.64) s vs.(144.75±11.45) s), and the differences between the two modes were statistically significant (t=8.665, −4.373; both P<0.05). Conclusion The target dose between the two modes were similar. The FFF mode can remarkably reduce the radiation dose of OAR and normal tissues, and can significantly shorten the time of DIBH therapy. -
图 2 左侧乳腺癌改良根治术后患者(女性,46岁)2种容积旋转调强放疗计划同一CT图像等剂量线分布比较 A为FFF-VMAT计划;B为FF-VMAT计划。A和B图从左至右依次为横断面、冠状面、矢状面图。FFF为非均整器;VMAT为容积旋转调强放疗;FF为均整器
Figure 2. Comparison of isodose distribution in the same CT images with two volumetric modulated arc therapy plans of a patient (female, 46 years old) with left breast cancer after modified radical mastectomy
表 1 16例左侧乳腺癌改良根治术后女性患者2种VMAT计 划的靶区剂量及机器参数比较(
)$ \bar{{x}}\pm {s} $ Table 1. Comparison of target dosimetric and machine parameters between the two volumetric modulated arc therapy plans in 16 female patients with left breast cancer after modified radical mastectomy (
)$ \bar{{x}}\pm {s} $ 参数 FFF-VMAT FF-VMAT t值 P值 D2%(cGy) 5640.22±70.09 5613.52±63.07 1.644 0.121 D50%(cGy) 5323.74±48.55 5307.29±51.74 1.462 0.164 D98%(cGy) 4881.38±32.21 4891.64±31.88 −1.386 0.186 适形指数 0.87±0.49 0.87±0.05 −0.490 0.631 均匀指数 0.14±0.02 0.14±0.01 1.415 0.178 梯度指数 3.24±0.66 3.30±0.67 −1.519 0.150 机器跳数(MU) 1073.41±143.79 815.70±87.69 8.665 <0.001 执行时间(s) 128.00±11.64 144.75±11.45 −4.373 0.001 注:FFF为非均整器;VMAT为容积旋转调强放疗;FF为均整器;Dx%表示x%靶体积的受照剂量 表 2 16例左侧乳腺癌改良根治术后女性患者2种VMAT计 划的危及器官剂量学比较(
)$ \bar{{x}}\pm {s} $ Table 2. Comparison of dosimetry of organs at risk of two volumetric modulated arc therapy plans in 16 female patients with left breast cancer after modified radical mastectomy (
)$ \bar{{x}}\pm {s} $ 参数 FFF-VMAT FF-VMAT t值 P值 心脏 V5 Gy(%) 32.19±7.18 34.27±7.29 −2.156 0.048 V30 Gy(%) 1.33±1.07 1.70±1.27 −2.632 0.019 Dmean(cGy) 508.50±84.96 587.43±126.48 −2.689 0.017 左肺(患侧肺) V5 Gy(%) 52.02±3.80 55.82±3.55 −4.741 <0.001 V10 Gy(%) 37.80±5.53 40.65±4.23 −2.494 0.025 V20 Gy(%) 27.45±4.82 29.19±3.94 −2.058 0.057 Dmean(cGy) 1418.31±136.02 1516.83±171.71 −2.467 0.026 右肺(健侧肺) V5 Gy(%) 12.83±2.57 13.59±3.04 −0.986 0.340 Dmean(cGy) 278.43±57.28 294.51±44.58 −0.908 0.378 全肺 V5 Gy(%) 34.88±3.14 36.96±3.92 −2.156 0.048 V10 Gy(%) 21.23±3.44 22.87±3.92 −2.320 0.035 V20 Gy(%) 12.55±1.93 13.71±1.61 −2.600 0.020 Dmean(cGy) 829.55±63.94 919.68±59.36 −3.928 0.001 右乳腺(健侧) V5 Gy(%) 23.41±4.06 23.41±3.99 0.001 0.999 Dmean(cGy) 425.96±88.41 435.89±92.34 −0.830 0.420 脊髓外放0.5 cm Dmax(cGy) 2677.70±471.84 2681.10±506.08 −0.064 0.950 Dmean(cGy) 627.55±159.14 610.19±162.16 1.184 0.255 患者受照剂量 V5 Gy(%) 25.71±3.74 27.48±3.74 −2.465 0.026 注:FFF为非均整器;VMAT为容积旋转调强放疗;FF为均整器;Vx Gy为≥x Gy体积占总体积的百分比;Dmean为平均剂量;Dmax为最大剂量 -
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