宫颈癌腔内联合组织间插植近距离治疗优化算法剂量学分析研究

Dosimetric analysis of the optimization algorithm for intracavitary/interstitial brachytherapy of cervical cancer

目的在宫颈癌腔内联合组织间插植近距离治疗(IC/ISBT)中,基于剂量学及生物学模型的帮助,进行图形优化(GO)、模拟退火逆向计划优化算法(IPSA)和混合逆向计划优化算法(HIPO)的比较分析,为宫颈癌IC/ISBT治疗优化方法的选择提供依据。方法选取65例接受影像引导下IC/ISBT的宫颈癌患者。所有患者后装治疗计划分别采用GO、IPSA、HIPO优化的方式制定3次,处方剂量高危临床靶区体积(HRCTV)D_(90)均为6 Gy。针对3种优化方案的用时、剂量-体积参数及放射生物学差异,采用非参数Friedman检验以及非参数Wilcoxon秩检验进行比较分析。结果逆向计划优化耗时均较正向计划耗时短,时间分别是GO 135.03 s、IPSA 46.53 s、HIPO 98.36 s,肿瘤靶区剂量中高剂量照射的V_(150%)(53.66%)在HIPO计划中略高,而高剂量照射的V_(200%)(30.29%)在GO计划中更高。GO的适形度指数(CI)(0.91)较其他计划更好,差异具有统计学意义(χ^(2)=69.98,P<0.001)。HIPO计划的膀胱与直肠的D_(1 cm)^(3)、D2 cm^(3)受照射量较低,小肠受照射量与其他计划差异无统计学意义(P>0.05)。HIPO计划中HRCTV的等效均匀生物有效剂量(EUBED)(12.35 Gy)比GO(12.23 Gy)、IPSA(12.13 Gy)高,膀胱处的EUBED在GO(2.38 Gy)计划中最低,直肠处的EUBED在HIPO(3.74 Gy)计划中最低,小肠的EUBED 3种优化方式未见明显差异(P>0.05)。3种优化计划预测的肿瘤控制率(TCP)差异无统计学意义(P=0.055),HIPO计划预测膀胱与直肠的正常组织并发症概率(NTCP)比GO、IPSA计划低(χ^(2)=12.95~38.43,P<0.01),小肠的NTCP未见明显区别(P>0.05)。结论3种优化方法中,两种逆向优化方式均较正向优化耗时短。GO计划较IPSA、HIPO计划更适形。HIPO计划可以增加靶区生物学覆盖剂量,减少膀胱与直肠处的最大物理或生物受照射量和NTCP。推荐优先使用HIPO作为宫颈癌IC/ISBT的优化算法。

Objective To provide a basis for selecting the optimization method for intracavitary/interstitial brachytherapy(IC/ISBT)of cervical cancer by comparing graphical optimization(GO),inverse planning simulated annealing(IPSA),and hybrid inverse planning optimization(HIPO)using dosimetric and radiobiological models.Methods This study selected 65 patients with cervical cancer who were treated with image-guided IC/ISBT.The afterloading therapy plans for these patients were optimized using GO,IPSA,and HIPO individually,with a prescription dose high-risk clinical target volume(HRCTV)D_(90)of 6 Gy.The non-parametric Friedman test and the non-parametric Wilcoxon rank test were employed to analyze the differences in duration,dose-volume parameters,and radiobiology between the three types of optimized plans.Results Inverse planning optimization(IPSA:46.53 s;HIPO:98.36 s)took less time than GO(135.03 s).In terms of gross target volume(GTV)dose,the high-dose irradiation V_(150%)(53.66%)was slightly higher in the HIPO-optimized plans,while the V_(200%)(30.29%)was higher in the GO-optimized plans.The GO-optimized plans had a higher conformity index(CI;0.91)than other plans,showing statistically significant differences.Compared with other plans,the HIPO-optimized plans showed the lowest doses of D_(1 cm)^(3)and D_(2 cm)^(3)at bladders and rectums and non-statistically significant doses at small intestines(P>0.05).In terms of the equivalent uniform biologically effective dose(EUBED)for HRCTV,the HIPO-optimized plans showed a higher value(12.35 Gy)than the GO-optimized plans(12.23 Gy)and the IPSA-optimized plans(12.13 Gy).Moreover,the EUBED at bladders was the lowest(2.38 Gy)in the GO-optimized plans,the EUBED at rectums was the lowest(3.74 Gy)in the HIPOoptimized plans,and the EUBED at small intestines was non-significantly different among the three types of optimized plans(P=0.055).There was no significant difference in the tumor control probability(TCP)predicted using the three types of optimized plans(P>0.05).The normal tissue complication probabilities(NTCPs)of bladders and rectums predicted using the HIPO-optimized plans were lower than those predicted using the GO-and IPSA-optimized plans(χ^(2)=12.95-38.43,P<0.01),and the NTCP of small intestines did not show significant differences(P>0.05).Conclusions Among the three types of optimization algorithms,inverse optimization takes less time than GO.GO-optimized plans are more conformal than IPSA-and HIPO-optimized plans.HIPO-optimized plans can increase the biological coverage dose of the target volume and reduce the maximum physical/biological exposure and NTCP at bladders and rectums.Therefore,HIPO is recommended preferentially as an optimization algorithm for IC/ISBT for cervical cancer.