螺旋断层放射治疗在儿童神经母细胞瘤全颅骨放疗中保护海马的计划设计

Hippocampus-Sparing with Helical Tomotherapy for Pediatric Neuroblastoma Whole Skull Radiotherapy

目的:用螺旋断层放射治疗(TOMO)的不同模式进行儿童全颅骨照射的计划设计,探讨TOMO全颅骨照射同时保护海马的调强技术。方法:取5例儿童高危神经母细胞瘤颅骨转移病例,全颅骨外扩3 mm且皮下内收3 mm形成计划靶区(PTV),海马区外扩5 mm形成海马保护区。使用Tomo HDTM治疗计划系统设计螺旋模式下的保护全脑(HT-BSRT)、保护海马(HT-HSRT)和6野径照模式下保护全脑(DT-BSRT)、保护海马(DT-HSRT)4种调强计划,处方剂量为21.6 Gy/12F。单因素ANOVA和配对t检验比较靶区、海马区及其他正常组织剂量。结果:5例病例的4种调强方式中,PTV受照95%处方量的体积都大于95%,HT-BSRT、HT-HSRT、DT-BSRT、DT-HSRT均匀性指数分别为0.046 4±0.013 2、0.094 5±0.053 4、0.108 6±0.027 9和0.133 2±0.040 4(P=0.013),适形度指数分别为0.625 40±0.039 88、0.638 30±0.023 40、0.589 00±0.041 40和0.615 00±0.034 19(P=0.198);海马平均剂量分别为(14.92±3.52)、(3.30±0.79)、(17.80±1.78)和(5.13±1.62)Gy(P<0.000 1),海马保护区平均剂量分别为(15.38±3.08)、(4.41±1.06)、(17.83±1.55)和(6.41±1.81)Gy(P<0.000 1)。结论:全颅骨照射同时保护海马较之仅保护全脑的TOMO调强计划在满足PTV剂量要求下,能显著降低海马区受照剂量,保护儿童神经认知功能。

Objective To discuss an optimal hippocampus sparing whole skull radiotherapy plan with helical tomotherapy（TOMO） for pediatric neuroblastoma skull metastases by comparing the dose distribution of plans with different intensity modulation patterns on TOMO. Methods Five cases of pediatric high-risk neuroblastoma skull metastasis were enrolled.The clinical target volume（CTV） of the whole skull and the hippocampus region were contoured. The planning target volume（PTV） was the CTV with a 3 mm expansion and a 3 mm subcutaneous shrink. The hippocampal avoidance（HA）region with a 5 mm volumetric expansion around the hippocampus was determined. Tomo HDTMtreatment planning system was used to generate 4 kinds of radiotherapy plans with a prescription dose of 21.6 Gy/12 F, including helical tomo-brain sparing radiotherapy（HT-BSRT）, helical tomo-hippocampus sparing radiotherapy（HT-HSRT）, six-field direct tomo-brain sparing radiotherapy（DT-BSRT） and direct tomo-hippocampus sparing radiotherapy（DT-HSRT）. Single factor ANOVA and paired t-test were performed to compare the dose distributions of target area, hippocampus region and other normal tissues.Results The volume of PTV receiving≥95% of prescribed dose was≥95% in all 5 cases. The homogeneity indexes of HTBSRT, HT-HSRT, DT-BSRT and DT-HSRT were 0.046 4±0.013 2, 0.094 5±0.053 4, 0.108 6±0.027 9 and 0.133 2±0.040 4,respectively（P=0.013）, and the conformity indexes were 0.625 40±0.039 88, 0.638 30±0.023 40, 0.589 00±0.041 40 and0.615 00±0.034 19, respectively（P=0.198）. The average doses of hippocampus in HT-BSRT, HT-HSRT, DT-BSRT and DTHSRT were（14.92±3.52）,（3.30±0.79）,（17.80±1.78） and（5.13±1.62） Gy, respectively（P〈0.000 1）, and the average doses of HA region were（15.38 ± 3.08）,（4.41 ± 1.06）,（17.83 ± 1.55） and（6.41 ± 1.81） Gy, respectively（P〈0.000 1）. Conclusion Compared with brain sparing TOMO radiotherapy, hippocampus sparing whole skull radiotherapy with helical tomotherapy for pediatric neuroblastoma skull metastases not only meets the dose requirement for PTV, but also significantly lowers the dose of hippocampus region and protects the neurocognitive function of children.