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该研究包括了8例颅底恶性肿瘤患者,表1详细列出了患者的临床特征、诊断和处方剂量。
患者 性别 年龄 RBE加权
剂量/Gy分次 单次RBE加
权剂量/Gy诊断 1 M 45 57.6 16 3.6 颅底脊索瘤 2 M 68 57.6 16 3.6 颅底脊索瘤 3 M 46 57.6 16 3.6 颅底脊索瘤 4 M 28 57.6 16 3.6 颅底软骨肉瘤 5 F 19 60.8* 16 3.8 颅底脊索瘤 6 M 54 57.6 16 3.6 颅底脊索瘤 7 M 34 57.6 16 3.6 颅底脊索瘤 8 M 50 57.6 16 3.6 颅底脊索瘤 * 病例5由于靶区远离重要危及器官,因此处方剂量略高。 -
图1所示为2例典型颅底肿瘤的CIRT和IMRT计划的横断面、冠状面和矢状面的剂量分布的比较,其中(a)为两野对穿照射的CIRT计划的剂量分布,(b)为两野交角照射的CIRT计划的剂量分布。统计学分析比较两张TPS计划PTV的V95、Dmean、CI和HI,结果显示V95二者之间无统计学差异,而Dmean、CI及HI均有统计学差异,且IMRT计划优于CIRT(表2)。
剂量学参数 CIRT IMRT P值 V95 91.060±10.630 98.060±1.150 0.106 Dmean 57.440±1.080 58.480±1.390 0.048 CI 0.359±0.174 0.202±0.032 0.031 HI 0.667±0.117 0.783±0.101 0.024 -
图2所示为1例典型病例的CIRT和IMRT的DVH比较,由于显示器官太多,为尽可能减少曲线之间的重叠,拆分为两个图展示。从图中可以看出,PTV、GTV的低剂量,IMRT计划更优,垂体、双侧视神经、双侧晶体的受照剂量CIRT计划更小。
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对脑干、垂体、左右视神经、视交叉、左右颞叶、左右内耳9个器官的最大剂量Dmax和平均剂量Dmean以及左右晶体的最大剂量Dmax进行配对t检验,结果显示脑干Dmean、左侧视神经Dmean、左侧晶体Dmax、右侧晶体Dmax两组之间存在统计学差异,CIRT计划优于IMRT计划,而视交叉Dmax方面,IMRT优于CIRT(P<0.05)。其他的OAR剂量两组进行统计学比较,其均值CIRT均优于IMRT,但无统计学差异(表3)。
危及器官 剂量学参数 CIRT IMRT P值 脑干 Dmax 34.17±10.91 38.91±6.80 0.539 Dmean 48.27±4.80 53.19±3.33 0.008* 垂体 Dmax 11.77±6.68 22.69±5.32 0.748 Dmean 49.19±14.42 48.22±13.59 0.988 视交叉 Dmax 38.72±19.52 38.79±18.17 0.034* Dmean 40.10±20.03 30.93±22.68 0.066 左侧视神经 Dmax 31.68±23.40 25.64±23.31 0.632 Dmean 28.84±20.61 30.33±26.54 0.030* 右侧视神经 Dmax 8.87±8.94 14.06±10.67 0.878 Dmean 33.40±27.99 33.96±21.79 0.223 左晶体 Dmax 15.09±15.45 17.37±14.61 0.000* 右晶体 Dmax 0.06±0.18 6.54±0.66 0.047* 左侧颞叶 Dmax 2.29±6.47 6.72±2.23 0.723 Dmean 50.08±12.72 49.06±12.39 0.099 右侧颞叶 Dmax 8.00±5.39 12.32±6.63 0.250 Dmean 54.54±9.66 52.89±12.39 0.225 左侧内耳 Dmax 13.64±6.79 15.99±10.11 0.882 Dmean 34.79±20.38 34.31±15.11 0.711 右侧内耳 Dmax 21.78±13.54 23.15±10.27 0.438 Dmean 37.08±13.38 34.52±12.65 0.803 * P<0.05 -
最小Hausdroff距离[15]定义为空间上两个体积上距离最近的点的距离,如果这两个体积相交,则定义HDmin为0,HDmin的计算使用MIM软件(V6.9.6)进行。通过计算IMRT和CIRT计划的所有OAR的HDmin,并使用公式3拟合HDmin和OAR的最大受照剂量Dmax之间的关系,结果如表4和图3所示。
拟合参数 CIRT IMRT a 58.98±4.37 47.34±4.88 b −1.07±0.18 −1.14±0.33 c −0.00±4.05 6.67±4.25 SSE 4 245 6 328 R-square: 0.913 9 0.832 1 RMSE: 7.067 8.628 将表4中的拟合结果代入式(3)中,并令Dmax-CIRT=Dmax-IMRT,即为图3中两条曲线交叉点的纵坐标,得到HDmin为7.1 mm,即当OAR和PTV之间的最小距离大于7.1 mm时,CIRT计划的OAR受量要显著地小于IMRT计划。
Dosimetric Comparison Between Carbon-ion Uniform Scanning Mode Radiotherapy and Photon IMRT in the Malignant Skull Base Tumors
doi: 10.11804/NuclPhysRev.40.2022063
- Received Date: 2022-05-08
- Rev Recd Date: 2022-08-03
- Publish Date: 2023-06-20
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Key words:
- skull base tumors /
- radiotherapy /
- ion radiotherapy /
- dosimetry
Abstract: Comparative analysis of the dosimetric differences between Chinese-produced heavy ion accelerator uniform scanning and photon intensity-modulated radiotherapy(IMRT) treatment plans in the treatment of skull base malignancies. A retrospective analysis of the treatment plans for 8 patients with skull base malignancies treated with the domestic heavy ion equipment (Heavy Ion Medical Machine, HIMM) using uniform scanning, including 7 chordoma and 1 chondrosarcoma. Carbon ion radiotherapy(CIRT) plans were designed using the ciPlan planning system (V1.0) from Lanzhou Kejintaiji Company, with a prescription dose of 57.6~60.8 Gy (RBE) in the planning target volume, delivered in 16 fractions of 3.6~3.8 Gy (RBE) per fraction. The treatment used a multi-leaf collimator(MLC) to adjust beam conformity, a ridge filter(RF) to spread-out the Bragg peak, and a bolus to adjust beam conformity at the distal end. A fixed horizontal nozzle was used at a couch angle of 0°, and the couch rotated 90° or 180° to achieve two-field intersecting or opposing fields. The photon IMRT plan used the Eclipse planning system (V13.5) from Varian company to design a fixed 5-field IMRT plan, with the same prescription dose as the CIRT plan. All plans were evaluated for dosimetric parameters based on organ-at-risk(OAR) dose limits, including target coverage, conformity index(CI), homogeneity index(HI), and OAR dose. There was no statistically significant difference in PTV V95 between the two plans (P=0.106), but Dmean, CI, and HI were statistically different, with the IMRT plan superior to the CIRT plan (P values of 0.048, 0.031, and 0.024, respectively). Regarding OAR dose, most OAR doses in the CIRT plan were smaller than those in the IMRT plan, but there was no statistically significant difference. However, the maximum dose to the optic chiasm, left and right lenses, and the mean dose to the brainstem and right optic nerve differed significantly between the two plans (P values of 0.034, 0.000, 0.047, 0.008, and 0.030, respectively). The distance between OAR and target volume was described using the minimum Hausdorff distance(HDmin), and when HDmin was greater than 7.1 mm, the CIRT plan was significantly superior to the IMRT plan. The uniform scanning CIRT was inferior to the photon IMRT plan in terms of target uniformity and conformity, but superior to the IMRT plan in terms of OAR dose. Whether the dosimetric advantages can be translated into clinical benefits remains to be further validated by clinical studies.
Citation: | Zhiqiang LIU, Xiaoyun MA, Shilong SUN, Qiuning ZHANG, Ruifeng LIU, Hongtao LUO, Xiaoli LU, Xiaohu WANG. Dosimetric Comparison Between Carbon-ion Uniform Scanning Mode Radiotherapy and Photon IMRT in the Malignant Skull Base Tumors[J]. Nuclear Physics Review, 2023, 40(2): 287-293. doi: 10.11804/NuclPhysRev.40.2022063 |