宫颈癌自适应调强放射治疗中物理剂量和生物等效剂量的应用研究

Application study of physical dose and bioequivalent dose in intensity-modulated radiotherapy for cervical cancer

目的 宫颈癌患者在调强放射治疗(IMRT)中因肿瘤退缩、危及器官体积改变以及放疗过程中摆位误差等综合因素共同导致剂量学改变,分析自适应与单程IMRT中物理剂量与2 Gy分次放射的生物等效剂量(EQD_(2))参数的临床意义。方法 选取62例宫颈癌根治性放疗患者,在放疗15次后再重新CT扫描,将初始计划Plan1移植到新的CT上并将第15次放疗摆位误差输入计划不确定性中形成移植计划sPlan2,并在新CT上再次设计新的计划,将第16次放疗摆位误差输入到计划不确定性中形成新的sPlan3,分析Plan1、sPlan2和sPlan3计划中靶区与危及器官的物理剂量和EQD_(2)参数的变化。结果 相较于Plan1,sPlan2中肿瘤靶区(GTV)和转移区域淋巴结肿瘤靶区(GTV_(nd))分别缩小了48.26%和29.49%(P<0.05)。sPlan2与sPlan3放疗在不同方向上锥形束CT(CB CT)的摆位误差大部分可以控制在5 mm以下。在靶区方面,sPlan2中PGTV_(nd)的98%体积所受剂量(D_(98))、eD_(98)、D_(95)、eD_(95)和肿瘤控制率(TCP)均低于Plan1 (P <0.05),PGTV_(nd)和PCTV的适形指数(CI)、eCI均高于Plan1(P<0.05);sPlan3中PGTV_(nd)的D_(98)、eD_(98)、D_(95)、eD_(95)和TCP均高于sPlan2 (P <0.05),PGTV_(nd)和PCTV的CI、eCI均低于sPlan2 (P<0.05)。在危及器官方面,sPlan2中肠道近似最大剂量(D_(2))、eD_(2)、正常组织并发症概率(NTCP)均高于Plan1,sPlan3中肠道D_(2)、eD_(2)、NTCP均低于sPlan2,差异均有统计学意义(P<0.05);sPlan2中直肠D_(2)、eD_(2)、NTCP均高于Plan1,sPlan3中直肠D_(2)、eD_(2)、NTCP均低于sPlan2,差异均有统计学意义(P<0.05)。结论 宫颈癌IMRT期间受解剖结构动态改变和摆位误差等因素影响,放疗剂量传递精确性有不确定性,对淋巴结及其附近区域的影响较大,二程定位放疗较单程放疗具有物理剂量和EQD_(2)优势,能提高PGTV_(nd)剂量并降低淋巴结邻近肠道、直肠的D_(2),二程放疗在宫颈癌IMRT中的临床应用价值较高。

Objective The dosimetric changes in cervical cancer patients during intensity-modulated radiotherapy(IMRT) were caused by a combination of factors such as tumor regression,changes in organs at risk,and positioning errors during radiotherapy.The clinical significance of comparing parameters between physical dose and equivalent dose in2 Gy/f(EQD_(2)) in adaptive and one-way IMRT were analyzed.Method A total of 62 patients with cervical cancer undergoing radical radiotherapy were selected.After 15 radiation treatments,they were re-scanned with CT.The initial plan Planl was transplanted to the new CT,and the positioning errors of the 15^(th) radiation treatment were input into the plan uncertainty to form the transplanted plan sPlan2.A new plan was designed on the new CT,and the positioning errors of the 16^(th) radiation treatment were input into the plan uncertainty to form a new sPlan3.The physical dose and EQD_(2) parameters of target areas and organs at risk in Plan1,sPlan2,and sPlan3 plans were discussed.Result Compared with Planl,the gross tumor volume(GTV) and planning gross tumor volume of metastatic regional lymph node(GTV_(nd)) in sPlan2were reduced by 48.26% and 29.49%,respectively(P<0.05).The cone-beam CT(CBCT) positioning errors of sPlan2 and sPlan3 radiotherapy in different directions can be mostly controlled within 5 mm.In terms of target areas,the dose received by 98% volume(D_(98)),eD_(98),D_(95),eD_(95),and tumor control probability(TCP) of PGTV_(nd) in sPlan2 were lower than those in Planl(P<0.05),the conformal index(CI) and eCI of PGTV_(nd) and PCTV in sPlan2 were higher than those in Planl(P<0.05),the D_(98),eD_(98),D_(95),eD_(95),and TCP of PGTV in sPlan3 were higher than those in sPlan2(P<0.05),the CI and eCI of PGTV_(nd) and PCTV in sPlan3 were lower than those in sPlan2(P<0.05).In terms of organs at risk,the approximate maximum doses(D_2),eD_(2),and normal tissue complication probability(NTCP) of the intestines in sPlan2 were higher than those in Planl(P<0.05),the D_(2),eD_(2),and NTCP of the intestines in sPlan3 were lower than those in sPlan2(P<0.05),the D_(2),eD_(2),and NTCP of the rectum in sPlan2 were higher than those in Plan 1(P<0.05),the D_(2),eD_(2),and NTCP of the rectum in sPlan3 were lower than those in sPlan2(P<0.05).Conclusion Accuracy of radiotherapy dose transfer is uncertain due to influencing factors,including dynamic changes of anatomical structure and placement errors during IMRT for cervical cancer,which has a greater impact on lymph nodes and their adjacent areas.The two-stage radiotherapy has advantages in both physical dose and EQD_(2) compared to one-way radiotherapy,which increase the dose of PGTV_(nd) and reduce the D_(2) of intestine and bladder adjacent to the lymph nodes.Two-stage radiotherapy has high clinical application value in IMRT for cervical cancer.