宫颈癌放疗高危临床靶区变化及其对累计吸收剂量的影响

Changes of high-risk clinical target volume in radiotherapy for cervix cancer and the impact on accumulated absorb dose

【摘要】目的：在宫颈癌放疗的全过程中，肿瘤的大小和位置都会改变。本研究观测高危临床靶区（HRCTV）在放疗期间变化程度，及这些变化对HRCTV累计吸收剂量的影响。方法：从我院2011年10月-2014年6月放疗结束的病人中任选22个病人，病人的体外放疗计划是基于放疗前的CT图像用VARIANECLIPSE制定，在CT图像上勾画出PTV。每个病人体外放疗共45Gy／25次。体外放疗两周后，开始体内放疗，每周1次，共4次28Gy。每次体内放疗前，基于病人的CT图像用NUCTRONONCENTRA制定内照射计划，在CT图像上勾画出HRCTV。每个病人有l组外照射计划CT图像和4组近距离治疗计划的CT图像。用ONCENTRA把近距离计划的CT图像导入ECLIPSE中，经过图像融合，观察测量4次体内放疗的HRCTV变化。观测外照射对每个HRCTV的D95变化。用HRCTV变形指数描述病人多次体内放疗之间HRCTV变化程度，用非PTV指数描述体外照射PTV不能完全覆盖体内放疗HRCTV的程度，用HRCTV相对于体外照射PTV剂量的相对剂量（RelativePTVDose，RPD）描述体外照射对HRCTV的累计剂量情况。结果：共计22个体外放疗计划和88个体内放疗计划被分析。HRCTV变形指数平均值为0．45±0．13，非PTV指数平均值为0．05±0．13，相对于体外照射PTV剂量的相对剂量为-0．02±0．13，RPD〉0共有50次，占56．8％（50／88），RPD=0共有8次，占9．1％（8／88），RPD〈0共有30次，占34．1％（30／88）。结论：宫颈癌每次体内放疗（时间间隔1周及以上）HRCTV变化较大，但基本都在外照射PTV内，HRCTV受到的累计体外照射剂量，大多数情况下不等于体外照射的处方剂量，在计算病人放疗累计剂量时，应针对每个病例具体分析。

Objective To observe the changes of high-risk clinical target volume （HRCTV） in radiotherapy for cervix cancer and the impact on accumulated absorb dose, in that the size and location of the tumor will change during the radiotherapy. Methods Between October 2011 and June 2014, 22 patients after the radiotherapy were randomly selected to undergo external beam radiotherapy （EBRT） set by VARIAN ECLIPSE based on the CT image before the radiotherapy. The EBRT dose was 45 Gy in 25 fractions, and the EBRT planning target volumes （PTV） were delineated on CT image.s. After about 2 weeks of EBRT, HDR brachytherapy （HDR BT） was initiated once a week, delivered to a dose of 28 Gy in 4 fractions. CT-image-based BT planning was performed at NUCLETRON ONCENTRA before HDR BT, and the BT HRCTV was delineated. Each patient had an image set for EBRT planning and four image sets for BT planning. The CT images of BT planning from NUCLETRON ONCENTRA were imported into VARINA ECLIPSE to observe and measure the changes of HRCTV in the four HDR BT, and to observe the impacts of EBRT on D95 at every HRCTV by images fusion. The changes among HRCTV were described by HRCTV Deformation Index （HI）I）, and the non-overlapping volume between HRCTV and PTV was indicated by nonoverlapping PTV index （NPI）, and the impact of EBRT on HRCTV cumulative dose was showed by the relative PTV dose （RPD）, HRCTV relative to the EBRT PTV prescribed dose. Results A total of 22 EBRT plans and 88 BT plans were analyzed. The mean values of HDI, NPI and RPD were 0.45±0.13, 0.05±0.13, and -0.02±0.13, respectively. The number of RPD〉0 was 50, and the number of RPD=0 was 8, while the number of RPD〈0 was 30, and the percentage of the above three cases were 56.8% （50/88）, 9.1%（8/88）, and 34.1%（30/88）, respectively. Conclusion HRCTV varied widely between BT for cervix cancer with time interval of one week or more, but basically was within EBRT PTV. In most cases, the cumulative EBRT dose of HRCTV was not equal to the EBRT PTV prescribed dose. In calculating the cumulative dose of the radiotherapy patient, the specific analysis of each ease should be performed.