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近年来,儿童恶性肿瘤越来越受到人们的关注。我国儿童恶性肿瘤的流行病学分析数据显示,虽然我国儿童恶性肿瘤的发病率低于世界平均水平,但病死率却与世界平均水平相当,且高于美国和日本[1]。中枢神经系统(central nervous system,CNS)肿瘤是儿童最常见的恶性实体肿瘤,其发病率位于儿童恶性肿瘤的第2位,约占所有儿童恶性肿瘤的20%。儿童CNS生殖细胞肿瘤(germ cell tumor,GCT)起源于原始生殖细胞,多发生于15岁以下的儿童,确诊时的年龄多为10~14岁[2]。目前,全中枢神经系统放疗(craniospinal irradiation,CSI)仍然是儿童CNS GCT的有效治疗方法。随着放疗技术的发展,CNS GCT患儿的总体生存时间延长,患儿及家属对生活质量的要求必然随之提高,而在放疗不良反应中最受关注的是神经认知功能障碍[3]。Redmond等[4]和Tada等[5]的研究结果表明,神经认知功能障碍的发生是由海马的神经干细胞损伤引起的。由于海马的神经干细胞的放射灵敏性高,其增殖与凋亡的速度与海马接受的剂量大小密切相关,我们认为行CSI引起的神经认知功能障碍可以通过减少海马的照射剂量得到改善。本研究通过对行CSI的CNS GCT患儿的影像学资料进行回顾性分析,比较基于海马保护的调强适形放射治疗(intensity-modulated radiation therapy,IMRT)与容积旋转调强放射治疗(volumetric modulated arc therapy,VMAT)的剂量学差异。
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2种计划的PTV的各剂量学参数的比较结果见表1,IMRT计划组和VMAT计划组都得到了较好的靶区剂量分布,CI分别为0.88±0.01和0.87±0.01,实现了较好的靶区适形,但2组没有表现出较大的适形差异,组间CI的差异无统计学意义(P>0.05);在靶区剂量均匀性方面,VMAT计划组优于IMRT计划组,HI分别为0.11±0.02和0.14±0.01,且差异有统计学意义(P<0.001)。
组别 D2%(Gy) D50%(Gy) D98%(Gy) 适形指数 均匀性指数 IMRT计划组(n=12) 32.76±0.26 31.59±0.26 29.30±0.28 0.88±0.01 0.14±0.01 VMAT计划组(n=12) 33.04±0.32 31.95±0.44 28.59±0.49 0.87±0.01 0.11±0.02 t值 1.976 1.895 −5.033 2.206 −5.392 P值 0.074 0.085 <0.001 0.249 <0.001 注:IMRT为调强适形放射治疗;VMAT为容积旋转调强放射治疗;D2%、D50%、D98%分别为2%、50%、98%的靶区体积受照剂量 表 1 IMRT与VMAT 2种计划的PTV的各剂量学参数比较(
)$ \bar x \pm s $ Table 1. Dosimetry comparison of planning target volume between intensity-modulated radiation therapy group and volumetric modulated arc therapy group (
)$ \bar x \pm s $ -
2种计划的海马的各剂量学参数的比较结果见表2,VMAT计划组左、右海马的Dmax和Dmean均显著低于IMRT计划组,且差异均有统计学意义(均P<0.001)。
组别 最大照射剂量 平均照射剂量 左海马 右海马 左海马 右海马 IMRT计划组(n=12) 21.21±1.07 21.35±0.69 17.80±3.06 17.61±2.92 VMAT计划组(n=12) 15.99±0.70 16.13±0.58 11.30±0.65 11.67±0.72 t值 −17.622 −21.628 −7.513 −6.780 P值 <0.001 <0.001 <0.001 <0.001 注:IMRT为调强适形放射治疗;VMAT为容积旋转调强放射治疗 表 2 IMRT与VMAT 2种计划的海马的受照剂量比较(
,Gy)$ \bar x \pm s $ Table 2. Dosimetry comparison of hippocampus between intensity-modulated radiation therapy group and volumetric modulated arc therapy group (
, Gy)$ \bar x \pm s $ -
由表3可知,VMAT计划组在眼晶状体、甲状腺和肾脏的保护方面优于IMRT计划组,且差异均有统计学意义(均P<0.05);2种计划在双肺的保护方面相当,差异均无统计学意义(均P>0.05)。VMAT计划组的低剂量区大于IMRT计划组,且差异有统计学意义[(11 287.31±1 475.92) cm3对(10 633.83±1 378.01) cm3,t=−11.119,P<0.01]。
组别 最大照射剂量 平均照射剂量 左眼晶状体 右眼晶状体 甲状腺 左肺 右肺 左肾 右肾 VMAT计划组 6.10±0.89 6.39±0.55 13.70±1.41 7.24±0.81 7.03±0.69 5.99±2.13 6.79±2.72 IMRT计划组 6.85±0.95 7.11±0.73 17.74±2.06 6.50±1.96 7.71±1.54 8.60±1.46 8.70±1.49 t值 −2.515 −2.894 −8.198 1.757 −1.760 −3.099 −2.231 P值 0.029 0.015 <0.001 0.107 0.106 0.010 0.047 注:IMRT为调强适形放射治疗;VMAT为容积旋转调强放射治疗 表 3 IMRT与VMAT 2种计划的周围危及器官的受照剂量比较(
,Gy)$ \bar x \pm s $ Table 3. Dosimetry comparison of organ at risk between intensity-modulated radiation therapy group and volumetric modulated arc therapy group (
, Gy)$ \bar x \pm s $ -
2种计划的机器跳数和治疗时长的比较结果见表4,VMAT计划组的机器跳数和治疗时长均仅为IMRT计划组的40%左右,且差异均有统计学意义(均P<0.001),这说明VMAT计划组的计划实施效率显著高于IMRT计划组。在计划验证方面,VMAT计划组的验证通过率同样高于IMRT计划组,且差异有统计学意义(P<0.05)。
组别 机器跳数 治疗时长(s) 验证通过率(%) IMRT计划组(n=12) 4 341±390 825±67 95.8±2.1 VMAT计划组(n=12) 1 749±95 354±31 98.6±1.2 t值 −20.883 −22.790 4.874 P值 <0.001 <0.001 0.005 注:治疗时长为治疗计划验证模式下统计的机器出束时长,并不包含患者摆位时间。IMRT为调强适形放射治疗;VMAT为容积旋转调强放射治疗 表 4 IMRT与VMAT 2种计划的计划实施效率比较(
)$ \bar x \pm s $ Table 4. Comparison of treatment efficiency between intensity-modulated radiation therapy group and volumetric modulated arc therapy group (
)$ \bar x \pm s $
基于海马保护的2种儿童中枢神经系统生殖细胞肿瘤放疗技术的剂量学研究
Dosimetry study of two radiotherapy techniques for child central nervous system germ cell tumor based on hippocampus protection
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摘要:
目的 比较容积旋转调强放射治疗(VMAT)和调强适形放射治疗(IMRT)2种技术在儿童中枢神经系统(CNS)生殖细胞肿瘤(GCT)放疗中的海马保护和剂量学差异。 方法 回顾性分析2020年6月至2021年6月在解放军联勤保障部队第九〇〇医院接受全CNS放疗的12例GCT患儿的影像学资料,其中男性患儿4例、女性患儿8例,年龄7~14岁,中位年龄11岁。对所有患儿进行靶区及周围危及器官的勾画,分别设计VMAT计划和IMRT计划,处方剂量30 Gy,每次3 Gy,共照射10次。通过剂量体积直方图获取各剂量学参数并进行配对t检验,比较靶区及周围危及器官的剂量学差异,通过比较机器跳数和治疗时长评估计划实施效率。 结果 VMAT和IMRT 2种技术均能得到较好的靶区剂量学分布。VMAT技术的靶区均匀性略优于IMRT技术,均匀性指数分别为0.11±0.02和0.14±0.01,且差异有统计学意义(t=−5.392,P<0.001)。VMAT和IMRT2种技术的左海马最大照射剂量分别为(15.99±0.70) Gy和(21.21±1.07) Gy、右海马最大照射剂量分别为(16.13±0.58) Gy和(21.35±0.69) Gy,且差异均有统计学意义(t=−17.622、−21.628,均P<0.001),VMAT技术在海马保护上达到了剂量限制要求。VMAT技术在周围危及器官保护方面较IMRT技术优势明显,除双肺外,在眼晶状体、甲状腺、肾脏保护方面VMAT技术全面优于IMRT技术,且差异均有统计学意义(t=−8.198~−2.231,均P<0.05)。VMAT技术在治疗效率方面同样优于IMRT技术,VMAT的机器跳数为1 749±95、治疗时长为(354±31) s,均仅为IMRT技术的40%左右,且差异均有统计学意义(t=−20.883、−22.790,均P<0.001)。 结论 在儿童CNS GCT放疗中,VMAT技术能够在保护海马的情况下实现更好的靶区均匀性,同时在周围危及器官保护和治疗效率上具有明显优势。 Abstract:Objective To compare dosimetry between volumetric modulated arc therapy (VMAT) and intensity-modulated radiation therapy (IMRT) for protecting the hippocampus in the radiotherapy of children with central nervous system (CNS) germ cell tumors (GCT). Methods Retrospective analysis was conducted on the imaging data of 12 children with GCT who received craniospinal irradiation in the 900th Hospital of the Joint Logistics Support Force of PLA from June 2020 to June 2021. The participants included 4 males and 8 females aged 7 to 14 years, with a median age of 11 years. VMAT and IMRT plans were designed after completing the delineation of the target area and the corresponding organs at risk. The prescribed dose was 30 Gy with 10 fractions. Dose-volume histogram was used to obtain various dosimetry parameters. The parameters were then analyzed using paired t-test to compare dosimetry between the target area and the corresponding organs at risk and evaluate the implementation efficiency based on machine monitor unit and treatment time. Results VMAT and IMRT plans both achieve better target dose distribution. VMAT is slightly better than IMRT in terms of the uniformity of the target area. The homogeneity index values for VMAT and IMRT are 0.11±0.02 and 0.14±0.01, respectively, and the difference is statistically significant (t=−5.392, P<0.001). The maximum doses of the left hippocampus in VMAT and IMRT are (15.99±0.70) and (21.21±1.07) Gy, and those of the right hippocampus are (16.13±0.58) and (21.35±0.69) Gy, respectively; the differences are statistically significant (t=−17.622, −21.628; both P<0.001). VMAT meets the dose limit for hippocampal protection and has obvious advantages over IMRT in protecting organs at risk. VMAT is significantly better than IMRT in protecting the eye lens, thyroid, and kidney, and the differences are statistically significant (t=−8.198 to −2.231, all P<0.05). In terms of treatment efficiency, VMAT is also superior to IMRT. The machine monitor unit of VMAT is 1749±95 and the treatment time is (354±31) s, which are about 40% of those of IMRT, and the differences are statistically significant (t=−20.883, −22.790; both P<0.001). Conclusion In the radiotherapy of childhood CNS GCT, VMAT can achieve better target uniformity while protecting the hippocampus and has obvious advantages in terms of protection of the corresponding organs at risk and treatment efficiency than IMRT. -
表 1 IMRT与VMAT 2种计划的PTV的各剂量学参数比较(
)$ \bar x \pm s $ Table 1. Dosimetry comparison of planning target volume between intensity-modulated radiation therapy group and volumetric modulated arc therapy group (
)$ \bar x \pm s $ 组别 D2%(Gy) D50%(Gy) D98%(Gy) 适形指数 均匀性指数 IMRT计划组(n=12) 32.76±0.26 31.59±0.26 29.30±0.28 0.88±0.01 0.14±0.01 VMAT计划组(n=12) 33.04±0.32 31.95±0.44 28.59±0.49 0.87±0.01 0.11±0.02 t值 1.976 1.895 −5.033 2.206 −5.392 P值 0.074 0.085 <0.001 0.249 <0.001 注:IMRT为调强适形放射治疗;VMAT为容积旋转调强放射治疗;D2%、D50%、D98%分别为2%、50%、98%的靶区体积受照剂量 表 2 IMRT与VMAT 2种计划的海马的受照剂量比较(
,Gy)$ \bar x \pm s $ Table 2. Dosimetry comparison of hippocampus between intensity-modulated radiation therapy group and volumetric modulated arc therapy group (
, Gy)$ \bar x \pm s $ 组别 最大照射剂量 平均照射剂量 左海马 右海马 左海马 右海马 IMRT计划组(n=12) 21.21±1.07 21.35±0.69 17.80±3.06 17.61±2.92 VMAT计划组(n=12) 15.99±0.70 16.13±0.58 11.30±0.65 11.67±0.72 t值 −17.622 −21.628 −7.513 −6.780 P值 <0.001 <0.001 <0.001 <0.001 注:IMRT为调强适形放射治疗;VMAT为容积旋转调强放射治疗 表 3 IMRT与VMAT 2种计划的周围危及器官的受照剂量比较(
,Gy)$ \bar x \pm s $ Table 3. Dosimetry comparison of organ at risk between intensity-modulated radiation therapy group and volumetric modulated arc therapy group (
, Gy)$ \bar x \pm s $ 组别 最大照射剂量 平均照射剂量 左眼晶状体 右眼晶状体 甲状腺 左肺 右肺 左肾 右肾 VMAT计划组 6.10±0.89 6.39±0.55 13.70±1.41 7.24±0.81 7.03±0.69 5.99±2.13 6.79±2.72 IMRT计划组 6.85±0.95 7.11±0.73 17.74±2.06 6.50±1.96 7.71±1.54 8.60±1.46 8.70±1.49 t值 −2.515 −2.894 −8.198 1.757 −1.760 −3.099 −2.231 P值 0.029 0.015 <0.001 0.107 0.106 0.010 0.047 注:IMRT为调强适形放射治疗;VMAT为容积旋转调强放射治疗 表 4 IMRT与VMAT 2种计划的计划实施效率比较(
)$ \bar x \pm s $ Table 4. Comparison of treatment efficiency between intensity-modulated radiation therapy group and volumetric modulated arc therapy group (
)$ \bar x \pm s $ 组别 机器跳数 治疗时长(s) 验证通过率(%) IMRT计划组(n=12) 4 341±390 825±67 95.8±2.1 VMAT计划组(n=12) 1 749±95 354±31 98.6±1.2 t值 −20.883 −22.790 4.874 P值 <0.001 <0.001 0.005 注:治疗时长为治疗计划验证模式下统计的机器出束时长,并不包含患者摆位时间。IMRT为调强适形放射治疗;VMAT为容积旋转调强放射治疗 -
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