中华放射医学与防护杂志  2017, Vol. 37 Issue (9): 713-716   PDF    
引用本文
王泽阳, 牛书雷, 高贞, 底学敏, 杜随, 张宏涛, 王娟. 粒子植入术后肿瘤缩小时不同布源方式对剂量的影响[J]. 中华放射医学与防护杂志, 2017, 37(9): 713-716, DOI: 10.3760/cma.j.issn.0254-5098.2017.09.015.
粒子植入术后肿瘤缩小时不同布源方式对剂量的影响
王泽阳1 , 牛书雷2 , 高贞1 , 底学敏2 , 杜随2 , 张宏涛1 , 王娟1     
1. 050000 石家庄, 河北省人民医院肿瘤一科;
2. 050017 石家庄, 河北医科大学研究生院
收稿日期: 2017-02-22
通信作者: 王娟, Email:niushulei167x@163.com
[摘要] 目的 假定125I粒子植入术后肿瘤每月以20%速度退缩时，研究等间距与周边密集、中间稀疏2种布源方式对剂量的影响。方法 利用计算机三维治疗计划系统（TPS）勾画4 cm×5 cm的圆柱形肿瘤，根据布源方式不同分为等间距组和周边密集、中间稀疏组，以处方剂量125 Gy载入放射性活度1.85×107Bq 125I粒子行术前计划。假设125I粒子植入肿瘤后肿瘤高不变，直径每月以20%的速度缩小，粒子随肿瘤均匀向心性集中，分别计算125I粒子植入术后0、1、2、3个月时90%靶体积吸收剂量（D90）、90%处方剂量覆盖体积占靶体积的百分比（V90）、150%处方剂量覆盖体积占靶体积的百分比（V150）。结果 等间距组载入粒子85颗，植入0、1、2、3个月后的D90分别为126.20、130.41、133.82和139.48 Gy，V90分别为97.0%、98.1%、99.3%和100%，V150分别为70.2%、69.9%、71.1%和71.5%；周边密集、中间稀疏组植入粒子75颗，植入0、1、2、3个月后的D90分别为126.46、125.41、123.50和128.83 Gy，V90分别为95.2%、95.7%、94.9%和97.6%，V150分别为52.8%、60.4%、62.7%和59.3%。结论 当肿瘤直径每个月以20%速度退缩时，粒子等间距分布时肿瘤预期吸收剂量逐渐增加；周边密集、中间稀疏的布源方式肿瘤预期吸收剂量不变，且高剂量区范围明显小于等间距布源。
[关键词] 125I粒子     治疗计划系统     布源方式     剂量     肿瘤退缩    
The dosimetric effect of different source patterns in case of tumor shrinkage after 125I seed implantation
Wang Zeyang1, Niu Shulei2, Gao Zhen1, Di Xuemin2, Du Sui2, Zhang Hongtao1, Wang Juan1     
1. Section I, Department of Oncology, Hebei Provincial People's Hospital, Shijiazhuang 050000, China;
2. Graduate School of Hebei Medical University, Shijiazhuang 050017, China
Corresponding author: Wang Juan, E-mail:niushulei167x@163.com
[Abstract] Objective To study the dosimetric effect of two source patterns, including equal spacing and peripheral dense intermediate sparse by assuming a tumor shrinking speed of 20% per month after 125I seed implantation. Methods A virtual cylindrical tumor with 4 cm in height and 5 cm in diameter was contoured on a three-dimensional treatment planning system (TPS). Two groups of preoperative plans were made with 1.85×107 Bq 125I seeds using two source patterns respectively. It was assumed that the tumor height was unchanged, while the diameter of tumor would decrease at a speed of 20% per month, and the locations of seeds would concentrate towards the tumor core. The 90% target volume dose (D90), the ratio of 90% isodose volume over the target volume (V90), and the ratio of 150% isodose volume over the target volume (V150) were calculated at 0, 1, 2, 3 months after 125I implantation respectively. Results In equal spacing group, 85 seeds were implanted. The values of D90 were 126.20, 130.41, 133.82 and 139.48 Gy after 0, 1, 2 and 3 months respectively. The values of V90 were 97.0%, 98.1%, 99.3% and 100%, while those of V150 were 70.2%, 69.9%, 71.1% and 71.5%. The dense in-periphery and sparse-in the middle group was loaded with 75 seeds. The D90 values were 126.46, 125.41, 123.50 and 128.83 Gy, the V90 95.2%, 95.7%, 94.9% and 97.6%, and the V150 52.8%, 60.4%, 62.7% and 59.3% after 0, 1, 2 and 3 months, respectiviely. Conclusions When the tumor diameter reduces at a rate of 20% per month after 125I seed implantation, the expected tumor dose absorption will gradually increase using the equal spacing sources pattern. However, the expected dose does not vary with source distribution of dense-in the-surrounding and sparse-in-middle, which also reduces high dose volume more than the equal spacing pattern.
[Key words] 125I seed     Treatment planning system     Sources pattern     Dose     Tumor shrinkage    

放射性粒子组织间永久性植入治疗是早期低危前列腺癌根治性治疗手段之一[1-2]。粒子植入剂量是保证其治疗效果的关键指标，美国国立综合癌症网络(NCCN)指南推荐单独应用放射性125I粒子植入治疗前列腺癌剂量为145 Gy[3]。布源方式和肿瘤体积缩小等是影响粒子植入剂量的重要因素。隋爱霞等[4]报道利用计算机三维治疗计划系统模拟周边分布和中心分布两种布源方式，结果显示粒子数目及活度相同时周边分布有较好的剂量。吴娟等[5]报道了以周边密集、中间稀疏为原则行125I粒子植入术后肿瘤靶体积缩小可显著影响剂量分布，认为肿瘤每个月以大于初始体积20%的速度缩小时，肿瘤靶区将受到高于处方剂量照射。而关于肿瘤缩小时不同布源方式行125I粒子植入治疗对剂量分布的影响少见报道。本研究利用治疗计划系统(TPS)，探讨125I粒子植入术后肿瘤每个月以20%速度退缩时不同布源方式对肿瘤预期吸收剂量的影响。

材料与方法

1.材料：计算机三维计划系统(3D-TPS)Prowess 3D Version 3.02，美国SSGI公司；放射性125I粒子6711-99型，外形为圆柱形钛合金封装体，直径为0.8 mm、长度4.5 mm，内有3.0 mm×0.5 mm的银柱吸附125I，其外是壁厚0.05 mm的钛壳。γ射线能量为27~35 keV，组织半价层2 cm，半衰期60.2 d，放射性活度1.85×107 Bq，由中国欣科医药公司生产。

2.研究方法：利用计算机三维治疗计划系统(TPS)勾画4 cm×5 cm，层厚0.5 cm的圆柱形肿瘤，等间距组布源方式为按照层内粒子间距1.0 cm，层间距1.0 cm，粒子距离肿瘤周边0.5 cm的等间距布源，以处方剂量为125 Gy载入1.85×107 Bq 125I粒子，实施肿瘤粒子植入治疗计划。周边稀疏、中间密集组布源方式为在等间距布源方式基础上，以不改变处方剂量为前提，调整全部层面肿瘤内粒子位置，具体为：在术前计划的基础上于每层左边第1根粒子针增加1颗125I粒子，3颗125I粒子头尾间距为0.75 cm，左边第2根粒子针上下两端粒子位置不变，去掉中间2颗125I粒子，于中间加1颗125I，3颗粒子之间两两间距为1.5 cm。左边第3根粒子针上下两端粒子位置不变，去掉中间3颗125I，于中间加上1颗125I粒子，3颗125I粒子之间两两间距为2 cm。左边第4根粒子针上粒子位置调增同第2根粒子针，左边第5根粒子针上粒子位置调增同第1根粒子针。假设125I粒子植入肿瘤后肿瘤高不变，直径每个月以20%的速度缩小，粒子随着肿瘤均匀向心性集中，分别计算125I粒子植入术后0、1、2和3个月时90%靶体积吸收剂量(D90)、90%处方剂量覆盖体积占靶体积的百分比(V90)、150%处方剂量覆盖体积占靶体积的百分比(V150)。

结果

等间距布源方式需要125I粒子数目(85颗)明显多于周边密集、中间稀疏的布源方式(75颗)。肿瘤直径每个月按照20%速度缩小时，等间距布源方式随着肿瘤缩小预期吸收剂量明显增加(表 1)。

表 1 肿瘤缩小时等间距和周边密集、中间稀疏两种布源方式粒子植入术后预期吸收剂量变化 Table 1 The changes of the expected dose in tumour when the tumor shrank after 125I seeds implantation, with equal spacing and peripheral dense intermediate sparse

讨论

放射性粒子植入治疗剂量是取得良好治疗效果的重要保证，术后验证剂量不足可导致肿瘤复发[6-9]，过高的剂量可能对周围危及器官造成严重的并发症。为此，美国近距离治疗协会(ABS)推荐肺癌125I粒子植入剂量为110~125 Gy[10]，而NCCN指南推荐单独使用125I粒子植入治疗前列腺癌剂量为145 Gy[3]。而影响剂量的因素是多种多样的，Lee等[11]利用TPS模拟前列腺癌125I植入，认为不同布源方式将显著影响粒子植入剂量。Kovtun等[12]和Shaikh等[13]报道前列腺癌粒子植入术后，由于前列腺癌水肿，体积增大，而待水肿消失后体积减小，周边危及器官尿道、直肠的受照剂量增加。吴娟等[14]报道125I粒子植入肺部肿瘤术后1个月肿瘤的靶体积明显减小，周边剂量D90及V90等体积参数均升高。提示布源方式及肿瘤退缩均可显著影响肿瘤实际吸收剂量。

本研究利用TPS模拟肿瘤直径每个月以20%的速度退缩时分别以周边密集、中间稀疏和等间距原则两种布源方式植入粒子，观察肿瘤吸收剂量的变化。结果显示，处方剂量相同时，等间距布源方式所需粒子数高于周边密集、中间稀疏布源方式。随着时间的延长和肿瘤的缩小，等间距布源方式肿瘤预期吸收剂量D90将逐渐升高，而周边密集、中间稀疏布源方式肿瘤预期吸收剂量D90则变化不大。等间距组的高剂量区(V150)明显高于周边密集、中间稀疏组，肿瘤缩小后，等间距组的高剂量区仍明显大于周边密集、中间稀疏且无明显动态变化。因此，在保证处方剂量的前提下推荐125I粒子植入使用周边密集、中间稀疏的布源方式，可明显减少125I粒子使用数目，且肿瘤直径每个月以20%速度退缩时，不增加肿瘤的吸收剂量，可能减少由于肿瘤缩小致使剂量升高而引起的并发症。

总之，随着放射125I粒子植入在治疗肿瘤方面的广泛应用，粒子植入术后肿瘤退缩，布源方式、粒子活度、肿瘤病理类型、肿瘤大小、术后剂量验证等因素均可影响肿瘤实际吸收剂量，使除前列腺癌以外的粒子植入工作更加复杂，为放射性粒子植入工作者提出了更高的要求。随着粒子植入研究的不断进展，综合考虑影响放射性粒子植入各个方面，制定放射性粒子植入的标准化流程，必将使这项技术给更多的肿瘤患者带来福音。

利益冲突 本文作者无影响研究结果的财务关系，在此对研究的独立性和科学性予以保证
作者贡献声明 王泽阳负责收集文献和论文撰写；牛书雷、底学敏、杜随负责实验实施、数据的收集及整理；高贞负责协助整理数据；张宏涛、王娟指导论文的撰写和修改
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