等效均匀剂量优化方法对肿瘤调强放疗计划中危及器官保护的研究

目的 探讨等效均匀剂量(EUD)优化方法对肿瘤调强放疗计划中危及器官的保护作用.方法 从已接受调强放疗的患者中用整群随机数字表法抽取鼻咽鳞状细胞癌8例、食管鳞状细胞癌10例、直肠癌6例,用物理约束条件优化设计放疗计划,将危及器官的物理约束条件改为EUD约束,同时保持靶区约束条件不变,为每例患者设计一个新计划,并比较新(PLANEU组)、旧(PLANNo_EUD组)治疗计划.结果 PLANEUD组8例鼻咽癌患者危及器官都得到了更好的保护,与PLANNOEUD组比较差异均有统计学意义(t值分别为2.590、2.352、3.656、2.148、2.283、3.683、2.192、2.353、2.146、2.276、2.126,均P＜ 0.05);10例食管癌患者危及器官受量两组比较,差异无统计学意义(t值分别为0.408、0.427、0.902,均P＜ 0.05);PLANEUD组6例直肠癌患者危及器官得到了更好的保护,与PLANNOEUD组比较差异均有统计学意义(t值分别为2.332、2.693、2.279、2.244,均P＜ 0.05).结论 在保证靶区剂量的同时,EUD优化方法能够降低危及器官的受照剂量,对减少正常组织放疗并发症具有重要意义,同时为靶区增量提供了空间.     

剂量体积联合等效均匀剂量优化在鼻咽癌调强放疗危及器官优化中的应用

目的 研究剂量体积优化（dose-volume, DV）联合等效均匀剂量（equivalent uniform dose, EUD）优化在鼻咽癌调强放疗危及器官优化中的应用。方法 选取西南医科大学附属医院肿瘤科放疗室鼻咽癌患者调强放疗计划55例,制作调强计划时优化方法分为常规DV优化法和DV与EUD联合优化法两种,比较两种优化方法优化后靶区与危及器官的受量。结果 常规DV优化和DV与EUD联合优化后肿瘤靶区处方剂量、均匀性指数与适形度指数之间差异均无统计学意义（均P>0.05）,危及器官平均剂量差异均有统计学意义,DV与EUD联合优化得到的危及器官平均剂量低于常规DV优化（均P<0.001）。结论 本研究将DV优化与EUD联合优化法成功应用于鼻咽癌调强放疗危及器官的优化中,并在此基础上提出一种调强计划危及器官受量的验收方法,减少调强放疗计划中人为主观因素对危及器官受量的影响。     

剂量体积联合等效均匀剂量优化在肝癌调强放疗中的应用

目的：探讨剂量-体积（dose-volume,DV）联合等效均匀剂量（Equivalent uniform dose，EUD）目标函数对肝癌调强放疗计划优化的影响。方法：随机选取20例原发性肝癌患者，对每例患者先做DV物理约束作为优化条件的计划，然后在保持物理约束条件不变的基础上，将危及器官增加最大EUD和靶区增加最小EUD的约束条件，重新优化计划。比较单纯使用DV目标函数优化计划和DV联合EUD目标函数优化计划对靶区和危及器官剂量学差异。结果：两组计划均能满足临床治疗要求。单纯DV优化和DV联合EUD优化（DV+EUD）的靶区剂量、CI和HI均无统计学差（P>0.05）；DV+EUD优化使正常肝的所受剂量较纯物理DV优化明显减小，同时肝，肾脏、胃、小肠等平均剂量也减低明显,差异具有统计学意义（P<0.05）。结论：DV+EUD优化应用到肝癌患者调强放射治疗中可以在满足靶区剂量临床要求的同时，更好地保护正常组织。     

局部进展期鼻咽癌快速旋转调强与固定野动态调强放疗的剂量学比较

目的 比较快速旋转调强与固定野动态调强放疗技术在局部进展期鼻咽癌治疗中的剂量学差异.方法 选取10例局部进展期鼻咽癌患者,采用两种治疗技术设计同步推量调强放疗计划.在满足95%计划靶体积达60 Gy情况下,比较两种计划的剂量体积直方图、靶区和危及器官剂量、机器跳数、治疗时间.结果 快速旋转调强与固定野动态调强放疗计划在局部进展期鼻咽癌治疗剂量学上无差异.快速旋转调强计划比固定野动态调强放疗技术的靶区平均剂量略升高,最大、最小剂量无差异,脑干、下颌骨及整个治疗区域正常组织受量降低,腮腺、视神经、晶体等危及器官剂量无差异.快速旋转调强计划比固定野动态调强放疗计划的总机器跳数平均减少了57%(589.5 MU:1381.0 MU),每次治疗时间平均减少了70%(2.33 min:7.82 min).结论 两种放疗技术的治疗计划剂量分布基本一致,均能满足临床治疗需要.快速旋转调强放疗每次治疗时间明显缩短,其总机器跳数的降低减少了正常组织受照剂量.     

等效均匀剂量优化法在肺癌调强放疗计划优化中的应用

目的:评估等效均匀剂量（EUD）优化法在肺癌调强放疗计划优化中的作用。方法:随机抽取10例治疗计划基于剂量-体积优化法得到,且已完成调强放射治疗的肺癌病例,将治疗计划中的危及器官全肺、心脏以及脊髓的约束条件改为EUD约束,保持其它优化条件不变,设计出新的治疗计划,比较新旧治疗计划的剂量学差异。结果:在靶区剂量分布没有差别甚至更好的情况下,基于EUD优化能够使全肺的V₂₀和D_mean分别降低2.1%、1.0Gy,心脏的D₃₃和D_mean分别降低2.2Gy、1.9Gy,脊髓的D_1cc降低6Gy,经配对t检验,差异均有统计学意义（P<0.05）。结论:EUD优化能够有效降低全肺、心脏以及脊髓的受照剂量,这对于降低肺癌患者放射治疗并发症具有重大意义,同时也为进一步提高肿瘤靶区剂量,提高肿瘤局部控制率提供了可能。     

鼻咽癌调强放疗过程中再次计划实施必要性的临床研究

鼻咽癌的调强放疗已逐渐得到广泛应用,与整体挡铅放疗相比,照射靶区剂量分布有明显改善,同时很大程度降低了周围正常组织和危及器官的受照剂量.鼻咽癌调强放疗的靶区剂量分布变化较大,势必需要尽可能提高定位精度和减少摆位随机误差,从而保证实际照射治疗剂量.本研究观察调强放疗中体积和横径改变以及靶区剂量变化,从而提出再次计划的必要性.     

相关统计分析模型在调强放疗计划优化过程中的应用

目的 研究相关统计分析模型在前列腺癌调强放疗计划优化过程的应用.方法 随机抽取5例前列腺癌的调强放疗计划,保持射野物理参数、靶区目标函数和优化参数不变,在优化过程中相继改变危及器官的等效均匀剂量(EUD)参数a、权重(w)、最大EUD(EUD_(max))值.应用相关性分析模型对剂量运算结果进行关联性(CF)和参数优化作用(OF)分析,得到有最佳剂量分布的优化参数a、w、EUD_(max)值域,将其代替原计划中的相应参数重新进行调强计划优化,并将计划结果与原计划进行比较.结果 OF分析显示各优化方法的优化作用存在明显差异,a、w优化对危及器官的体积剂量基本无优化作用(OF<0.01),但对剂量热点和平均剂量有较强优化作用(OF≈1).CF分析显示各危及器官剂量与计划靶体积(PTV)(V_(95))的关联性在a、w优化时存在差异,差异与靶区和危及器官间距离呈正比.将各最优参数值MOR{a}、MOR{w}、MOR{EUD_(max)}赋给原计划重新进行剂量优化,剂量结果显示危及器官的平均受照剂量明显减少,PTV平均剂量更接近处方剂量,剂量体积直方图和等剂量分布图显示新计划剂量分布较好.结论 通过相关统计分析模型能准确地确定前列腺癌调强放疗计划优化参数值的最佳选择范围,高效率得到在较大程度上能满足临床要求的调强治疗计划.     

鼻咽癌调强放疗受照剂量分布特性研究

目的研究鼻咽癌调强放疗(IMRT)受照剂量分布特性。方法用拓能公司WiMRT放疗计划系统分别进行鼻咽癌常规放疗和调强放疗计划设计,对比分析不同放疗方式下正常组织受照剂量-体积直方图和所需照射的总跳数。结果调强放疗射野内正常组织受照剂量低于28Gy的体积是常规放疗的1.43~1.81倍,而高于35Gy时,受照体积仅为常规放疗的0.73~0.30倍。结论鼻咽癌调强放疗时靶区受照剂量高、正照组织受照剂量低,但正常组织受照体积大。鼻咽癌调强放疗剂量分布明显优于常规放疗。     

利用DVH图分析鼻咽癌调强放疗中正常器官体积剂量的变化

目的：应用剂量体积直方图（DVH）,研究鼻咽癌患者在放疗过程中正常器官体积及剂量的变化。方法：接受全程调强放疗（IMRT）的20例初治鼻咽癌患者,在治疗20次时,按原固定体位和参考坐标重新CT扫描,设计计划,与原计划进行比较DVH图中正常器官（眼球、晶状体、视神经、腮腺、脊髓及脑干）体积剂量的变化。结果：DVH2上左右腮腺体积明显小于DVH1（P〈0.05）,左右腮腺和脊髓的最大剂量和平均剂量明显增加,脑干最大剂量变化有统计学意义（P=0.011）,其中腮腺的剂量增加与放疗所致的腮腺缩小程度有一定相关性,其余无统计意义。结论：鼻咽癌IMRT过程中正常器官（特别是腮腺）体积剂量会发生一些变化,建议放疗中后期有必要重新勾画靶区,重新计划,减小正常器官的受照量,减少放疗反应。     

乳腺癌术后逆向调强放射治疗方案的比较研究

目的：比较不同照射野的逆向调强放疗方案，研究符合临床要求的乳腺癌术后最佳治疗方案。方法：对8例左侧乳腺癌术后进行预防照射，采用5、7、9、11和13个照射野5种方法分别制订逆向调强计划，使用相同的剂量一体积约束条件进行逆向优化，靶区平均剂量50Gy，选择剂量最佳方案进行治疗，比较这5个计划的剂量分布、剂量体积直方图（DVH）、适合度指数（CI）、不均匀指数和危及器官的剂量体积值等指标。结果：11～13个野的逆向调强计划可使临床靶区体积（CTV）获得满意的剂量分布。随着照射野数目的增加，靶区剂量均匀性、适合度指数提高，而5种照射方案相比，除了右肺外，其余危及器官的受照射剂量差异无统计学意义。P〉0．05。结论：11～13个调强照射野可使乳腺癌术后调强治疗获得理想的剂量分布，而不会增加各个危及器官的受照剂量。     

鼻咽癌容积调强旋转放疗和固定野适形调强放疗的剂量学对比

目的:对比旋转容积调强技术（RapidArc ）和固定野适形调强放疗（intensity modulated radiation therapy ,IMRT）治疗鼻咽癌剂量学方面的差异,探索不同T 分期从何种技术获益最大。方法:选取60例无远处转移鼻咽癌患者,按鼻咽癌2008分期T 1～2期20例,T 3 期20例,T 4 期20例。使用瓦里安公司Eclipse 系统,每例患者分别制定RapidArc 和固定野IMRT 计划,比较两者靶区覆盖、危机器官剂量、跳数和治疗时间的差别。结果:IMRT 和RapidArc 均能满足临床要求,靶区剂量分布差异无统计学意义（P >0.05）,均匀性和适形性相当。按T 分期分层比较,T 4 期患者RapidArc 组PGTV、PTV 1、PTV 2 的靶区剂量较高（P < 0.05）,PGTV 均匀指数较好（P = 0.059）。 RapidArc 组视神经、晶体、颞叶、腮腺V 20、喉、颞颌关节受照剂量均较低（P < 0.05）。 按T 分期分层比较,脑干剂量T 1～2 期、T 3 期两组比较差异无统计学意义（P > 0.05）,T 4 期患者脑干D 1% 、Dmax剂量RapidArc 组较IMRT 组低（P < 0.05）。RapidArc 和IMRT 相比,治疗跳数节省65% ,治疗时间节省63% 。结论:RapidArc 和9 野IMRT 治疗鼻咽癌均可满足临床要求,Rap?idArc 可明显降低正常器官剂量,缩短治疗时间,减少治疗跳数。对局部早、中期（T 1～3 期）患者,两者有相似的靶区剂量分布,但对局部晚期（T 4 期）患者,RapidArc 更具有将高剂量区集中在靶区而减少正常器官受照剂量的优势。      

Nasopharyngeal carcinoma. Treatment planning with IMRT and 3D conformal radiotherapy

The study was undertaken in order to compare dose plans for intensity-modulated radiotherapy (IMRT) with 3D conformal radiotherapy (3D-CRT) dose plans in patients with nasopharyngeal carcinoma (NPC). Clinical data from 20 consecutive patients treated with IMRT are presented. For 11 patients 3D-CRT plans were made and compared to the IMRT plans with respect to doses to the planning target volumes (PTVs) and to organs at risk (OARs). For comparison of the conformation of dose to defined target volumes the conformity index (CI) was used. Target volume coverage and critical organ protection were significantly improved with IMRT compared to 3D-CRT. One-year loco-regional control, distant metastasis-free survival, and overall survival were 79%, 72%, and 80%. Two patients have had recurrence in the clinical target volume (CTV) only and seven patients have relapsed in distant organs and/or in head-and-neck areas outside the target areas. The study confirms that IMRT is superior to 3D-CRT in the treatment of NPC. As locoregional control of NPC improves we are facing an increasing number of recurrences outside the irradiated area.     

Is uniform target dose possible in IMRT plans in the head and neck?

: Various published reports involving intensity-modulated radiotherapy (IMRT) plans developed using automated optimization (inverse planning) have demonstrated highly conformal plans. These reported conformal IMRT plans involve significant target dose inhomogeneity, including both overdosage and underdosage within the target volume. In this study, we demonstrate the development of optimized beamlet IMRT plans that satisfy rigorous dose homogeneity requirements for all target volumes (e.g., ±5%), while also sparing the parotids and other normal structures.

: The treatment plans of 15 patients with oropharyngeal cancer who were previously treated with forward-planned multisegmental IMRT were planned again using an automated optimization system developed in-house. The optimization system allows for variable sized beamlets computed using a three-dimensional convolution/superposition dose calculation and flexible cost functions derived from combinations of clinically relevant factors (costlets) that can include dose, dose-volume, and biologic model-based costlets. The current study compared optimized IMRT plans designed to treat the various planning target volumes to doses of 66, 60, and 54 Gy with varying target dose homogeneity while using a flexible optimization cost function to minimize the dose to the parotids, spinal cord, oral cavity, brainstem, submandibular nodes, and other structures.

: In all cases, target dose uniformity was achieved through steeply varying dose-based costs. Differences in clinical plan evaluation metrics were evaluated for individual cases (eight different target homogeneity costlets), and for the entire cohort of plans. Highly conformal plans were achieved, with significant sparing of both the contralateral and ipsilateral parotid glands. As the homogeneity of the target dose distributions was allowed to decrease, increased sparing of the parotids (and other normal tissues) may be achieved. However, it was shown that relatively few patients would benefit from the use of increased target inhomogeneity, because the range of improvement in the parotid dose is relatively limited. Hot spots in the target volumes are shown to be unnecessary and do not assist in normal tissue sparing.

: Sparing of both parotids in patients receiving bilateral neck radiation can be achieved without compromising strict target dose homogeneity criteria. The geometry of the normal tissue and target anatomy are shown to be the major factor necessary to predict the parotid sparing that will be possible for any particular case.     

中晚期鼻咽癌调强放疗生物等效剂量优化的可行性探讨

目的:对调强放射治疗(IMRT)中靶区与器官不同分次剂量的生物效应进行计划优化设计,评价和探索以生物等效剂量条件改善中晚期鼻咽癌IMRT计划质量的可行性.方法:选择IMRT计划20例鼻咽癌患者,按治疗分次和线性二次模型设定危及器官的等效剂量限制条件并重新进行治疗计划的优化计算.分析和比较生物等效剂量优化计划(BEPlan)与原物理剂量优化计划(PHPlan)的结果,包括靶区适形性指数(CI)、剂量均匀性指数(HI)、危及器官平均剂量和最大剂量等参数.结果:与PHPlan比较,BEPlan处方剂量包绕的靶区体积(TV95％)无明显差别,CI和HI分别改善了8.03％和8.33％,较靠近靶区的危及器官剂量略有上升但生物等效剂量远小于各器官的剂量限制值.结论:采用等效剂量优化方法有助于提高治疗计划的靶区剂量适形性和均匀性.     

Eclipse最小剂量参数对鼻咽癌调强计划影响的研究

目的:探讨Eclipse鼻咽癌调强计划中最小剂量参数(Minimize dose)对靶区和危及器官受照剂量的影响，为临床计划优化提供参考。方法:运用Varian Eclipse 10.0计划系统回顾性对10例鼻咽癌患者重新设计调强计划，采用相同的约束条件，最小剂量参数分别选取5、8、10、15、20。比较靶区适形度指数和均匀性指数、危及器官照射剂量或受照体积、机器跳数和子野数，并做统计学分析。结果:最小剂量参数由5增大到20，靶区CI减小，HI增大，OARs受照剂量增加。统计学比较显示当最小剂量为8时PCTV1 HI的P值首次小于0.05（P=0.031），差异有统计学意义。当最小剂量大于等于10时全部靶区的CI和HI的P＜0.05，差异有统计学意义。脑干和脊髓从最小剂量参数为10开始P<0.05（P=0.025,P=0.008），统计学比较差异显著。右侧腮腺和下颌骨在最小剂量参数大于等于15时P<0.05（P=0.041，P=0.005），差异有统计学意义。随最小剂量参数的增大，总机器跳数由2 186.3±175.7减少到2 085±149.5，无统计学差异。子野数由1 603.3±278.0减少到1 567.4±270.0，最小剂量参数大于等于10时差异有统计学意义。结论:考虑最小剂量参数对靶区、危及器官、机器跳数和子野数的影响，Eclipse鼻咽癌调强计划中最小剂量参数选择5到8之间是合适的。     

腮腺分区勾画对伴有双侧颈部Ⅱ区淋巴结转移鼻咽癌调强放射治疗计划优化的影响

[目的]探讨腮腺分区勾画对伴有双颈部Ⅱ区淋巴结转移鼻咽癌调强放射治疗计划优化的影响。[方法]选择接受调强放疗的双颈部Ⅱ区淋巴结转移的鼻咽癌患者20例,利用Corvus6．3调强治疗计划系统设计3种治疗计划：既未进行腮腺分区勾画的常规计划（Pian01：将腮腺沿下颌后静脉前外缘作与腮腺后界的平行线,将腮腺分成前外与后内两部分,分别予剂量限制,重新计划优化,得到将腮腺分区勾画的计划（Planl）;将腮腺分区勾画的CT序列定义为模体,由常规计划（Plan0）进行正向运算得到计划2（Plan2）。比较Planl与Plan2在靶区和正常组织的剂量分布。『结果]两套计划均符合RTOG0615靶区及正常组织剂量限制要求。采用该腮腺分区勾画方法能够降低整个腺体的平均辐射剂量、V15以及〈20Gy体积,这主要归功于降低了腮腺前外侧区约20％的平均辐射剂量、30％～40％的V。[结论]在伴有双颈部Ⅱ区淋巴结转移鼻咽癌IMRT中,腮腺分区勾画在理论上和剂量学上具有可行性,尤其降低了干细胞集中部位（腮腺前外侧区）的辐射剂量．具有一定推广应用价值,对腮腺分泌功能的影响有待前瞻性随机试验证实。     

Intensity modulated and three-dimensional conformal radiation therapy plans for oropharyngeal cancer: a comparison of their sensitivity to set-up errors and uncertainties

We compared the effect of set-up error and uncertainty on two radiation therapy treatment plans for head and neck cancer: one using intensity modulated radiation therapy (IMRT) and one using conventional three-dimensional conformal radiation therapy (3D-CRT). We used a Pinnacle3 (Philips Medical Systems, Markham, Ontario) system to create the two treatment plans (7-beam IMRT and 5-beam 3D-CRT) for the same volumetric data set, based on the objectives and constraints defined in the Radiation Therapy Oncology Group H-0022 protocol. In both plans, the dose-volume constraints for the targets and the organs at risk (oars) were met as closely as the beam geometries would allow. Monte Carlo-based simulations of set-up error and uncertainty were performed in three orthogonal directions for 840 simulated "courses of treatment" for each plan. A systematic error (chosen from distributions characterized by standard deviations ranging from 0 mm to 6 mm) and random uncertainties (2 mm standard deviation) were incorporated. We used a probability approach to compare the sensitivities of the IMRT and the 3D-CRT plans to set-up error and uncertainty in terms of equivalent uniform dose (EUD) to targets and oars.Based on the EUD analysis, the targets and oars showed considerably greater sensitivity to set-up error with the IMRT plan than with the 3D-CRT plan. For the IMRT plan, target EUDS were reduced by 4%, 7.5%, and 10% for 2-mm, 4-mm, and 6-mm set-up errors respectively. However, even with set-up error, the mandible, spinal cord, and parotid EUDS always remained lower with the IMRT plan than with the 3D-CRT plan.We conclude that, when quantified by EUD, IMRT-plan doses to oars and targets are more sensitive to set-up error than are 3D-CRT-plan doses. However, as judged by the differences between target and OAR doses, IMRT retains its superiority over 3D-CRT, even in the presence of set-up error.     

Intensity-modulated radiation therapy (IMRT) dosimetry of the head and neck: a comparison of treatment plans using linear accelerator-based IMRT and helical tomotherapy

PURPOSE: To date, most intensity-modulated radiation therapy (IMRT) delivery has occurred using linear accelerators (linacs), although helical tomotherapy has become commercially available. To quantify the dosimetric difference, we compared linac-based and helical tomotherapy-based treatment plans for IMRT of the oropharynx. METHODS AND MATERIALS: We compared the dosimetry findings of 10 patients who had oropharyngeal carcinoma. Five patients each had cancers in the base of the tongue and tonsil. Each plan was independently optimized using either the CORVUS planning system (Nomos Corporation, Sewickly, PA), commissioned for a Varian 2300 CD linear accelerator (Varian Medical Systems, Palo Alto, CA) with 1-cm multileaf collimator leaves, or helical tomotherapy. The resulting treatment plans were evaluated by comparing the dose-volume histograms, equivalent uniform dose (EUD), dose uniformity, and normal tissue complication probabilities. RESULTS: Helical tomotherapy plans showed improvement of critical structure avoidance and target dose uniformity for all patients. The average equivalent uniform dose reduction for organs at risk (OARs) surrounding the base of tongue and the tonsil were 17.4% and 27.14% respectively. An 80% reduction in normal tissue complication probabilities for the parotid glands was observed in the tomotherapy plans relative to the linac-based plans. The standard deviation of the planning target volume dose was reduced by 71%. In our clinic, we use the combined dose-volume histograms for each class of plans as a reference goal for helical tomotherapy treatment planning optimization. CONCLUSIONS: Helical tomotherapy provides improved dose homogeneity and normal structure dose compared with linac-based IMRT in the treatment of oropharyngeal carcinoma resulting in a reduced risk for complications from focal hotspots within the planning target volume and for the adjacent parotid glands.     

The impact of dental metal artifacts on head and neck IMRT dose distributions.

BACKGROUND AND PURPOSES: To quantify the cold or hot spot induced in IMRT treatment plans due to the presence of metal artifact in CT image data sets stemming from dental work. PATIENTS AND METHODS: Metal artifact corrected image data sets of five patients have been analyzed. IMRT plans were generated using five different planning image data sets: (a) uncorrected (UC) (b) homogeneous uncorrected (HUC), (c) sinogram completion corrected (SCC), (d) minimum value corrected (MVC), and (e) image set (d) subsequently corrected with a streak artifacts reduction algorithm (SAR-MVC). The SAR-MVC data set is assumed to be the closest approximation to the absence of metal artifacts and has therefore been taken as the reference image data set. An IMRT plan was generated for each of the image datasets (a)-(e). The resulting IMRT treatment plans for data sets (a)-(d) were then projected onto the reference data set (e) and recalculated. The reference dose distribution (e) was then subtracted from these recalculated dose distributions. Using dose difference analysis, the cold and hot spots in organs at risk (OARs) and the target volumes (TVs) were quantified. RESULTS: When compared to the reference dose distribution, the UC, HUC, and SCC plans exhibited hot spots showing on average more than 1.0 Gy hot dose in the left and right parotids. For the UC, HUC, and SCC recalculated plans, subvolumes of the clinical target volumes (CTV) were under dosed on average by more than 0.9 Gy. On the other hand, the MVC plan showed less than 0.3 Gy hot dose in both parotids, and the cold dose in the CTVs were reduced by up to 0.8 Gy. CONCLUSIONS: The presence of dental metal artifacts in head and neck planning CT data sets can lead to relative hot spots in OARs and relative cold spots in regions of the TVs when compared to the reference data set that more closely approximates the patient anatomy. This effect can be reduced if a simple minimum value correction (MVC) method for the dental metal artifacts is employed.     

鼻咽癌IMRT和VMAT计划对机器跳数和MLC误差剂量学敏感度对比研究

目的 模拟机器跳数(MU)和多叶准直器(MLC)叶片位置在计划执行时可能产生的系统误差,检测并分析鼻咽癌静态IMRT和VMAT计划对上述误差的剂量学敏感度。方法 选取5例已行IMRT的鼻咽癌计划,在相同物理参数的基础上重新制定VMAT计划,修改两组计划的MU,引入1.25%、2.50%、5.00%系统误差;同时修改计划的MLC原始文件,引入0.25、0.50、1.00、1.50、2.00 mm系统误差,模拟治疗计划执行过程中可能出现的叶片不到位情况。其中MLC系统误差的运动方式为两侧MLC叶片朝同个方向运动和两侧MLC叶片朝相反方向运动(射野外扩或内收)。采用线性回归分析法计算并比较IMRT和VMAT计划相对于MU和MLC系统误差的剂量学敏感度差异。结果 随着MU系统误差增加,IMRT和VMAT计划的靶区和OAR受量呈线性增加,且满足R²=0.992~1(P<0.05);对于MLC的误差,IMRT和VMAT计划的靶区和OAR相应剂量学参数的偏移误差引起的敏感度最小,分别为-0.26%/mm和-0.65%/mm;其次是外扩误差4.87%/mm和8.68%/mm,最大的是内收误差-6.04%/mm和-9.88%/mm。此外,3种类型误差中VMAT计划由误差引起的剂量学敏感度大于IMRT计划。结论 MU和MLC的系统误差对鼻咽癌IMRT计划的剂量分布有显著影响,尤其是VMAT计划。做好加速器MLC的日常QA工作对更好、更精确地实施放疗计划有着重要的意义。