应用4D-CT技术确定肝癌内靶体积及相关剂量学研究

Internal Target Volume Definition Using Four-dimensional CT and Dosimetric Evaluation for Hepatocellular Carcinoma

背景与目的:由于肝脏肿瘤的位移受呼吸运动的影响显著,三维适形放射治疗(three-dimensionalconformalradiotherapy,3DCRT)难以准确定位靶区。本研究应用4D-CT技术确定个体化肝癌内靶体积(internaltargetvolume,ITV),比较3D计划与4D计划的计划靶体积(planningtargetvolume,PTV)及相关剂量学差异,并评价4D-CT的优势。方法:选择7例原发性肝癌患者,行4D-CT门控扫描,在10个相位的CT图像中分别勾画大体肿瘤体积(grosstumorvolume,GTV)和临床靶体积(clinicaltargetvolume,CTV)。在20%呼吸时相CT图像中利用三维治疗计划系统根据PTV-3D、PTV-4D为每例患者设计两套放疗计划:3D计划与4D计划。PTV-3D由CTV外扩常规的安全边界得到;PTV-4D由10个时相的CTV融合形成的ITV-4D外扩摆位边界(SM)得到。两套计划的处方剂量、射野方式均相同。比较两套计划中靶区体积、靶区与危及器官的剂量学、正常组织并发症概率的差异。结果:PTV-3D、PTV-4D的体积分别为(417.60±197.70)cm3、(331.90±183.10)cm3,后者体积减少20.50%(12.60%～34.40%);两者靶区覆盖率与剂量分布均匀性无显著性差异;4D计划中危及器官(肝、肾、胃、小肠)的受照剂量均较3D计划降低,以肝最为显著。肝V30、V40分别由38.77%、27.32%降至33.59%、22.62%;正常肝平均剂量由24.13Gy下降为21.50Gy;肝并发症概率由21.57%下降为15.86%;在不增加正常组织并发症的前提下,4D计划的处方剂量可由(50.57±1.51)Gy提升至(54.86±2.79)Gy,平均提高9.72%(4.00%～16.00%)。结论:3D计划存在遗漏靶区或过度扩大靶区的缺陷。应用4D-CT技术可在3DCRT的基础上准确定位肝癌靶区,进一步减少正常组织的受照剂量,并提升靶区剂量。

BACKGROUND ＆ OBJECTIVE： Accurate definition of target volume is difficult in three-dimensional conformal radiotherapy （3D CRT） for liver tumors because of the wide moving extent of tumors with respiration. This study was to define individualized internal target volume （ITV） using four-dimensional computed tomography （4D-CT）, and compare planning target volumes （PTVs） and dose distribution of 3D planning with 4D planning for hepatocellular carcinoma （HCC）. METHODS.. Seven primary HCC patients received 4D-CT scanning. Gross tumor volumes （GTVs） and clinical target volumes （CTVs） were contoured on all 10 respiratory phases of CT images. The 3D and 4D treatment plans were made for each patient using different PTVs, namely, PTV-3D derived from a single CTV plus conventional margins; PTV-4D derived from ITV-4D which encompassing all 10 CTVs plus setup margins （SM）. The two plans were designed at the 20% respiratory phase CT images using 3D treatment planning system and compared with respect to PTVs, dose distribution to normal tissues, normal tissue complication probability. The prescription dose and design of irradiating fields were identical for both plans. RESULTS. The average PTV was （417.6±197.7） cm^3 in 3D plan and （331.9±183.1） cm^3 in 4D plan, decreased by 20.50% （12.60%-34.40%）. PTV coverage and dose uniformity were similar in the 2 plans. 4D plans spared more normal liver, kidney, stomach, and small intestine than 3D plans, especially for the liver. The V30 and V40 of the liver were lower in 4D plans than in 3D plans （33.59% vs. 38.77%, 22.62% vs. 27.32%）; the mean dose to normal liver was decreased from 24.13 Gy to 21.5 Gy; liver complication probability was decreased from 21.57% to 15.86%. Without increasing the normal tissue complication probability, the prescription dose was higher in 4D plans than in 3D plans [（54.86±2.79） Gy vs. （50.57±1.51） Gy], increased by 9.72% （4%-16%）. CONCLUSIONS：The 3D plans have pitfalls of geometric miss or over coverage of target volume. The 4D plans can accurately definite target volume to spare more normal tissues and make dose escalation as compared with 3D CRT.