非小细胞肺癌自适应放疗剂量学研究

  目的  探索非小细胞肺癌实施自适应放疗后危及器官(肺、心脏、脊髓)受照剂量的变化, 及危及器官受照剂量降低后靶区处方剂量的变化。  方法  12例局部晚期非小细胞肺癌患者在放疗过程中均行两次定位CT扫描, 以实行自适应放疗。通过MIM软件, 将两次计划进行融合。比较实行自适应放疗后, 保证靶区剂量不变的情况下, 危及器官的受量有无降低; 以及在保证正常组织器官受照剂量与原计划相似的情况下靶区剂量提升的空间。  结果  自适应放疗后, 在保证靶区受照剂量不变的情况下, 肺部V20平均降低3.53%, V30降低2.55%, 而全肺平均受照剂量降低2.11 Gy; 心脏V30平均降低4.19%、V40降低3.72%;脊髓最大受量平均降低3.52 Gy。危及器官受量与不行自适应放疗时相似的情况下, 靶区(PGTV)照射剂量平均提高1.25 Gy。  结论  非小细胞肺癌放疗过程中, 适时行自适应放疗能够减少周围危及器官的受照剂量, 提高靶区(PGTV)的处方剂量。      

鼻咽癌螺旋断层放射治疗过程中实际受照射剂量的研究

  目的  通过螺旋断层放射治疗（tomotherapy）系统的自适应模块,分析鼻咽癌患者靶区和危及器官的剂量在治疗过程中与初始计划的差异,为临床提供帮助。  方法  回顾性分析2014年2月至2015年2月昆明医科大学第一附属医院运用tomotherapy系统治疗的10例鼻咽癌患者,通过tomotherapy系统中的自适应模块和Mimvista 6.50软件的计算,将初始计划定义为Plan 1;进行图像引导患者总的实际受照射剂量定义为Plan 2。比较两项计划中肿瘤靶区及危及器官的剂量学差异。  结果  Plan 2中计划靶区体积（planning gross target volume,PGTV）的D98、D95的剂量较Plan 1分别下降11.91%、6.88%（P=0.001,P=0.006）。Plan 2中左侧腮腺的Dmean、D50较Plan 1分别增加42.23%、63.82%（P＜0.001、P=0.001）;Plan 2中右侧腮腺的Dmean、D50较Plan 1分别增加38.64%、66.76%（P=0.002,P=0.004）。Plan 2中脊髓的D2剂量较Plan 1也明显增加,增加了16.49%（P=0.026）。  结论  鼻咽癌患者在行tomotherapy过程中,非常有必要进一步纠正因解剖结构和摆位所带来的误差,保证放疗计划的精准性。      

基于MR超长期延迟强化量化分析鼻咽癌放疗GTV退缩规律的研究

  目的  探讨基于MR超长期延迟强化扫描对鼻咽癌（nasopharyngeal carcinoma,NPC）肿瘤靶区及淋巴结不同区域差异性退缩规律的研究。  方法  选取2019年12月至2020年8月山东省肿瘤医院53例接受放疗的NPC患者,获得放疗前、中及后MR（T2WI、15s强化及>10 min超长期延迟强化的T1WI像）。在T2WI上确定大体肿瘤靶区（GTVp）和淋巴结（GTVn）。根据15 s强化与>10 min强化T1WI的剪影图像确定造影剂清除比较快的区域（GTVp_快、GTVn_快）,清除慢的区域（GTVp_慢、GTVn_慢）,分析不同亚靶区放疗后的退缩差异性。  结果  1）GTVp在接受50 Gy及放疗结束的退缩率分别为57.37%、18.61%,低于GTVp_快的64.52%、29.66%,而显著高于GTVp_慢的25.21%、7.55%（P<0.05）,GTVn、GTVn_快、GTVn_慢的退缩也具有相似变化趋势;2）放疗前、后GTVp_快与GTVp、GTVn_快与GTVn体积变化均具有相关性（r=0.872、0.998,P<0.05）。而GTVp_慢与GTVp、GTVn_慢与GTVn体积变化差异无统计学意义（P<0.05）;3）放疗后GTVp_慢与接受50 Gy放疗时相比体积增加了7.55%,而GTVp与GTVp_快、GTVp_慢的退缩均小于淋巴结。  结论  MR超长期延迟强化扫描可以将NPC及阳性淋巴结分为造影剂清除快、慢的亚区域,不同亚区域及整体靶区退缩显著不同步;在以体积为标准进行NPC放疗疗效评估时,不同亚区域应行个体化分析。      

宫颈癌图像引导下调强放疗中危及器官变化对靶区的影响

目的 探讨晚期宫颈癌患者调强放疗中危及器官体积及位置变化对靶区的影响。方法 选取行图像引导下调强放疗宫颈癌患者16例，分别于放疗剂量达9 Gy/5f、18 Gy/10f、27 Gy/15f、36 Gy/20f及48.6 Gy/27f时用锥束CT（CBCT）扫描，采集CBCT图像，与原始治疗计划CT图像配准，分别在CT和CBCT图像中勾画大体肿瘤靶区及危及器官，比较危及器官体积、体积变化率及DICE相似度指数（dice's similarity coefficient，DSC） 。结果 放疗0~27分次膀胱、直肠、乙状结肠与小肠体积范围分别为88.48~195.49 cm³、40.41~42.93 cm³、792.85~907.86 cm³、38.49~49.05 cm³。膀胱0~27 分次体积变化差异有统计学意义（P=0.002），其余器官体积变化差异无统计学意义（P>0.05）。膀胱、直肠、乙状结肠及小肠0~27分次体积变化率和DSC差异均无统计学意义（P＞0.05）。膀胱、直肠体积变化率与宫颈靶区、宫体的DSC均呈负相关（P<0.05）。结论 宫颈癌调强放疗中膀胱、直肠等体积与位置变化较大，其变化可能影响宫颈靶区、子宫体的空间位置。     

广义等效均匀剂量优化法在左侧乳腺癌调强放疗中的剂量学研究

目的:探讨左侧乳腺癌根治术后调强放疗中广义等效均匀剂量的生物优化法的剂量学优势。方法:选取我院2020年01月到2020年12月30例接受调强放射治疗的左侧乳腺癌患者,每例患者计划靶区均采用剂量-体积的物理优化法;并行危及器官左肺和心脏采用单约束物理优化法（Plan1）、多约束物理优化法（Plan2）以及广义等效均匀剂量的生物优化法（Plan3）,右肺、脊髓及其外放的约束条件保持不变,分别评价三组计划的优劣;串行危及器官脊髓及其外放仅采用单约束物理优化法（Plan3）以及广义等效均匀剂量的生物优化法（Plan4）,左右肺、心脏的约束条件保持不变,分别评价两组计划的优劣。结果:采用不同优化方法的三组计划Plan1、Plan2和Plan3;以及采用不同优化方法的两组计划Plan3和Plan4靶区的适形度指数CI和均匀性指数HI差异均无统计学意义（P＞0.05）。并行危及器官左肺和心脏的剂量Plan3最优,其次是Plan2,最差是Plan1;串行危及器官脊髓及其外放的剂量Plan4优于Plan3且差异均有统计学意义（P＜0.05）。结论:广义等效均匀剂量的生物优化法可有效降低危及器官受量且不影响靶区的适形度指数CI以及均匀性指数HI,值得临床中推广使用。     

鼻咽癌调强放疗射野方向对急性放疗反应的影响

  目的  比较两种不同射野方案的鼻咽癌调强计划及其导致的急性放疗反应，确定出一种合理的射野方案。  方法  随机选20例鼻咽癌患者，应用飞利浦Pinnacle 8.0计划系统进行设计。其中10例患者采用IMRT-7P方案进行治疗，即调强放疗（IMRT）7野后半平面的均分布野方案；另10例患者采用IMRT-7A方案，即IMRT7野均分的布野方案。再分别模拟出对应的后半平面野和均分野计划，进行剂量学比较。比较参数为计划靶区的覆盖、均匀指数（HI）和适形指数（CI）以及危及器官（OARs）。观察并比较两组患者急性放疗反应。  结果  两组计划具有相似的靶区覆盖、HI和CI，IMRT-7P对保护脑干、脊髓、腮腺和颌下腺，具有一定的优势（P < 0.05），特别是保护了口腔。口腔的D_MEAN:（29.3±1.3）Gy，（35.7±2.3）Gy，P < 0.01；V₃₀:（36.2±5.4）%，（73.1±10.9）%，P < 0.01；V₄₀:（13.3±3.8）%，（29.0±9.7）%，P < 0.01。IMRT-7P所治疗的患者在口干、口腔黏膜炎、皮肤损伤和体质量下降上急性放疗反应更轻（P < 0.05）。  结论  鼻咽癌IMRT-7P治疗方案能一定程度上减少危及器官的剂量，更好的保护危及器官，减轻了急性放疗反应。      

造影剂对食管癌调强放疗剂量分布的影响

目的:比较有无造影剂对食管癌放疗靶区及危及器官剂量分布的影响。方法:选择食管癌患者12例,分别采集平扫和增强的CT断层图像传入计划系统。在增强CT图像上勾画靶区、危及器官和设计优化调强放疗计划。采用两种比较方案:①将勾画轮廓及计划复制到CT平扫上重新计算与原计划进行比较;②将勾画轮廓及优化条件复制到CT平扫上重新优化计算后与原计划进行比较。结果:Body、PTV、肺、心脏的电子密度在有造影剂时较高。方案①靶区在D_2%、D_50%、D_95%、D_98%、Body_95%、CI和HI有造影剂的情况下的计划小于平扫。两者之间的机器跳数（MU）没有统计学差异。危及器官肺V₅、V₂₀、D_mean;心脏V₄₀及D_mean;脊髓最大剂量在有造影剂的情况下较少。方案②两者在靶区D_2%、D_50%、D_95%、D_98%、Body_95%、CI、HI;肺V₅、V₂₀、D_mean;心脏V40及D_mean;脊髓最大剂量之间无统计学差异。在MU方面,无造影剂时较少。结论:静脉注射造影剂对食管癌调强放疗剂量分布的影响很小,临床上可以接受这样的误差,但在平扫上优化治疗计划可以得到更精确的剂量。     

食管癌多原发肿瘤调强放疗与三维适型放疗的剂量学对比研究

  目的  在食管多原发癌中比较三维适型、静态调强、容积调强放疗计划的剂量分布。  方法  中山大学肿瘤防治中心放疗科收治的7例食管多原发癌患者, 利用CT模拟定位勾画靶区, 临床靶区包括全食管及全纵隔淋巴结引流区, 计划靶区为临床靶区外扩5 mm, 同时设计3DCRT、7野IMRT和单弧VMAT计划, 比较各个放疗计划靶区及危及器官受照射剂量体积。  结果  靶区内最低剂量IMRT与VMAT明显高于3DCRT[D99:(49.4±0.8)Gy, (49.2±0.7)Gy, (43.9±2.8)Gy, P < 0.001];IMRT、VMAT与3DCRT计划比较, 双肺V30稍低、V5明显升高(V30:11.8%±2.5%, 10.5%±2.1%, 13.2%±2.1%, P=0.096;V5:92.5%±3.2%, 93.6%±5.6%, 68.5%±2.1%, P < 0.001);心脏V30明显减少, 脊髓最高剂量明显降低。VMAT与IMRT计划在靶区均匀性、危及器官照射剂量体积无明显差异, VMAT较IMRT治疗时间明显缩短[(3.0±0.6)min, (6.2±0.2)min, P < 0.001]。  结论  调强设计明显改善处方剂量95%以上剂量覆盖的靶区体积, 降低心脏的V30及脊髓最高剂量, 但同时明显增加全肺V5体积。由于V5体积高于目前的推荐限制剂量, 调强设计全食管/全纵隔放射治疗需要谨慎。另外单弧VMAT与IMRT计划剂量分布无明显区别, 可使治疗时间缩短52%。      

扩散张量成像在脑胶质瘤术后调强放疗中的临床应用初探*

目的:探讨扩散张量成像（diffusion tensor imaging,DTI）在指导邻近皮质脊髓束（corticospinal tract,CST）脑胶质瘤术后放疗方案中的应用价值。方法:30例邻近CST 脑胶质瘤术后拟行放疗患者,行常规MRI 平扫+ 增强及DTI 检查。获取CST 相关数据并与相应的MR、CT解剖图像融合,导入放疗计划系统并依此勾画靶区、危及器官及CST ,采用调强放疗（IMRT）技术分别制定考虑和不考虑CST 剂量保护的两种放疗计划并进行比较。结果:在两种计划均达到靶区治疗剂量及常规危及器官保护的情况下,考虑CST 剂量保护的放疗计划中的患者患侧、健侧CST 所受最大辐射剂量和平均辐射剂量均低于不考虑CST 剂量保护的放疗计划（P<0.05）。 结论:DTI 能够明确CST 的位置、形态及与脑胶质瘤术后放疗靶区的关系,有助于制定保护性放疗方案,最大程度减低CST 所受辐射剂量,从而降低放疗后发生神经损伤的可能。      

脑胶质瘤放疗靶区确定的方法学研究

探讨脑胶质瘤放疗靶区的确定方法。方法：9例脑胶质瘤患者用核磁共振（magneticreso-nance,MR）勾画靶区,然后通过软件分别与计算机断层扫描（computed tomography,CT）图像融合,把在MR所勾画的肿瘤区（gross tumor volume,GTV）及水肿区覆盖在CT图像上,通过CT图像的电子密度来计算吸收剂量并设照射野。结果：通过CT与MR在勾画靶区上的不同体积比较,MR上勾画靶区体积往往大于在CT上勾画靶区体积,GTV平均增大18.1%,水肿区平均增大29.0%,计划靶区（planning target volume,PTV）平均增大40.1%,并可更清晰地区分GTV与水肿区。结论：初步研究结果提示,在脑胶质瘤靶区确定方面,MR有着CT无可比拟的优势。对于脑胶质瘤Ⅲ及Ⅳ级,水肿区为亚临床病灶（clinical target volume,CTV）,而对于脑胶质瘤Ⅱ级,水肿区为GTV。     

鼻咽癌螺旋断层治疗的剂量学研究

目的 通过HT观察鼻咽癌患者放疗过程中肿瘤及OAR的照射剂量与计划剂量的差别,为临床提供帮助。方法 对21例采用HT根治性放疗的鼻咽癌患者,于CT下定位并勾画靶区及OAR。每次治疗前均进行MVCT扫描,应用MVCT图像在HT的自适应模块上进行剂量重建,得到当次的受照剂量,并模拟出该次无图像引导下的受照剂量;将各单次剂量分布和对应的融合CT图像传输至形变软件MIM6.0中进行剂量叠加,得到总照射剂量。将初始计划定义为Plan-1,图像引导的计划为Plan-2,无图像引导的计划为Plan-3,t检验或Wilcoxon符号秩检验三者靶区、OAR的剂量分布情况。结果 图像引导下的Plan-2较Plan-1的pGTV、PTV-1的D₉₈分别降低1.16%、2.3%(P=0.025、0.043);左右腮腺体积平均缩小46.0%、46.5%(P=0.000);左右腮腺质心距体中线垂直距离分别缩短6.9%、6.5%(P=0.000);双侧腮腺的V₂₆、D_mean分别升高32.8%和25.2%(P=0.000)。无MVCT引导的Plan-3较Plan-1的pGTV、PTV-1、PTV-2的D₉₈分别降低2.0%、1.9%、2.4%(P=0.001、0.007、0.036);双侧腮腺的V₂₆、D_mean分别升高33.6%、25.3%(P=0.000);脊髓D_max升高6.9%(P=0.005)。Plan-2中脊髓的D₂与Plan-1相近(P=0.392)。结论 鼻咽癌HT过程中双侧腮腺剂量升高,且与腮腺向体中线移位密切相关。图像引导对于靶区剂量获益并不大,但可减少脊髓受量。     

鼻咽癌IMRT中气腔对靶区及OAR剂量影响

目的 明确IMRT中气腔效应对鼻咽癌患者原发肿瘤及OAR受照射剂量影响。 方法 选择鼻咽癌患者9例,放疗前及放疗第25次分别接受CT定位扫描。在放疗前CT图像上勾画靶区及OAR,制定计划plan1。复制plan1,将此放疗前CT图像与放疗第25次CT图像融合。在放疗前CT图像上勾画靶区退缩后形成的空腔并将空腔的密度强制设为0,并将放疗前勾画的靶区减去空腔体积形成新靶区,此CT图像命名为CT_Air。使用plan1计划的设野及计划参数,在CT_Air上计算剂量分布,形成放疗计划plan2。假设plan1和plan2分别被全程使用,配对t检验比较有气腔和无气腔情况下原发肿瘤及OAR受量。     

Radiotherapy treatment planning of basal meningiomas: improved tumor localization by correlation of CT and MR imaging data.

A localization technique, based on three-dimensional CT and MR imaging data for precision radiotherapy of basal meningiomas, is presented. Indications for radiotherapy included unresected tumors, gross disease remaining despite surgery, and recurrences. The patient's head was fixed in a stereotactic localization system which is usable at the CT, MR and the linear accelerator installations. The geometrical distortion of MR imaging data was evaluated in three dimensions by phantom measurements. The geometrical distortion was "corrected" (reducing displacements to the size of a pixel) by calculations based on modelling the distortion as a fourth order two-dimensional polynomial. The target volume was defined in three-dimensional MR imaging data after application of 0.1 mmol/kg b.w. Gd-DTPA solution and transferred precisely from MR onto CT data to provide a map of the radiation attenuation coefficient for dose calculation. The superior soft tissue contrast of MR showed an excellent tumor delineation especially when the bony base of the skull obscured the target in CT images. Target volume, calculated dose distribution, and critical structures could be transferred between CT and MR imaging data and displayed as three-dimensional shaded structures for better assessment for matching of target volume and dose distribution. With the described planning system a more precise target definition of basal meningiomas was possible by integration of the superior tumor delineation in MR compared with CT.     

组织补偿膜添加方式引起的放疗剂量差异研究

目的：比较组织补偿膜添加方式引起的放疗剂量差异。方法选取2014年10—12月间乳腺癌根治术后需行胸壁放疗的20例患者,每例进行两种CT扫描。 CT－1：不加组织补偿膜直接扫描;CT－2：放疗体表添加组织补偿膜后再扫描。在放疗计划系统中为CT－1添加虚拟等效组织补偿膜,做满足临床要求的放疗Plan－1;再通过图像融合、计划验证等方法,把Plan－1移植到CT－2上,得到“平常用虚拟等效组织补偿膜做计划,而在放疗时体表加组织补偿膜的放疗Plan－2”;最后用CT－2做满足临床要求的放疗Plan－3。通过SPSS 19．0软件将Plan－2分别与Plan－1、Plan－3的临床数据进行t检验。结果 Plan－2与Plan－1、Plan－3的全肺V20（ P＝0．871、0．265）、患肺V20（ P＝0．170、0．290）、心脏V30（P＝0．074、0．190）、健侧乳腺Dmax（P＝0．556、0．240）,差异均无统计学意义;但计划靶区V50（P＝0．002、0．002）、V55（ P＝0．049、0．043）、CI （ P＝0．010、0．010）、HI （ P＝0．033、0．035）、机器总跳数（ P＝0．034、0．041）,差异均有统计学意义;且靶区层面剂量分布、照射野跳数分布也明显不同。结论体表添加等效组织补偿膜后再行CT扫描,所做计划才能真实反应计划靶区剂量分布和OAR受量。     

诱导化疗对局部晚期鼻咽癌IMRT剂量学影响及再计划剂量学特点分析

目的 通过研究诱导化疗对局部晚期鼻咽癌IMRT剂量学的影响及诱导化疗后再计划的剂量学特点,探讨诱导化疗后再计划的优特点,为临床合理设计放疗计划提供数据。方法 16例鼻咽癌患者诱导化疗前后各行1次增强CT扫描定位,并分别勾画靶区和制作放疗计划,分别定义为Plan-1及Plan-2。将诱导化疗后的靶区结构拷贝到第1段计划,融合生成第3段靶计划,定义为Plan-1-2。配对t检验Plan-1与 Plan-1-2、Plan-2与Plan-1-2靶计划的剂量学参数差异。结果 Plan-1与Plan-1-2:Plan-1-2 靶区Dmean明显降低(P<0.05);虽然脑干Dmean及颞叶Dmax明显降低,脊髓Dmean和Dmax均明显增加(P<0.05);靶区CI明显降低,HI明显增加(P<0.05);Plan-2与Plan-1-2:Plan-2 GTV、PGTV的Dmin和Dmean均明显增加(P<0.05);颞叶Dmean及脊髓Dmean和Dmax明显降低,其中脊髓Dmax降低达430.48 cGy (P<0.05);靶区CI明显增加,HI明显降低(P<0.05)。结论 诱导化疗后第1段IMRT靶计划剂量学分布变差,诱导化疗后再计划更有剂量优势。     

CT与MR图像融合在鼻咽癌放射治疗大体肿瘤靶区勾画中的应用

目的探讨CT与MR图像融合在鼻咽癌放射治疗大体肿瘤靶区(GTV)勾画中的临床应用价值。方法40例鼻咽癌患者均在1周内分别进行CT和MR扫描。全部CT和MR图像传送至荷兰核通公司PLATO放射治疗计划系统,进行图像融合。由4位有经验的放疗科医师对CT靶区和CT与MR融合图像大体肿瘤靶区(GTV)进行勾画及评价分析。结果经t检验,融合图像对GTV的显示明显优于单独CT图像。医师对CT-MR融合靶区勾画一致性较好。结论CT-MR图像融合技术有利于鼻咽癌靶区的确定,从而提高临床医师对鼻咽癌大体肿瘤靶区(GTV)进行勾画的准确率,有利于患者的诊治。     

图像引导对宫颈癌放疗中直肠、膀胱照射剂量的影响

目的 分析宫颈癌根治性外照射图像引导与否对直肠和膀胱受照剂量的影响,探讨IGRT技术合理应用的模式。方法 选取2012—2016年于陆军总院行HT的宫颈癌患者20例。每次治疗前均进行MVCT扫描,应用MVCT图像在HT的自适应模块上进行剂量重建,得到当次的受量,并模拟出该次无图像引导下的受量;将各单次剂量分布和对应的融合CT图像传输至形变软件MIM6.0中进行剂量叠加,得到总照射剂量。对比图像引导与否对直肠及膀胱受量和体积的影响。结果 无图像引导的Plan-2的直肠和膀胱受量均高于图像引导下的Plan-1,其中直肠Dmax、V50及膀胱V50均不同(P=0.040、0.000、0.047);分次间初次治疗的Dmax和V50及治疗第13~21次的直肠V50与Plan-1比差异有统计学意义(P=0.047、0.037,P=0.009、0.017、0.028),首次及21~23次放疗的膀胱Vmax、V50与Plan-1比接近有统计学意义(P=0.061、0.053,P=0.072、0.058)。结论 图像引导可以降低直肠和膀胱的受照剂量及体积,尤其是直肠从图像引导获益更大;建议外照射半量左右(13次左右),肿瘤退缩明显时段,重新定位修改治疗计划;对于难以实现全程图像引导的情况下,进行选择性的图像引导,也可以达到有效地降低直肠和膀胱损伤发生的效果。     

Dosimetric and geometric evaluation of an open low-field magnetic resonance simulator for radiotherapy treatment planning of brain tumours.

BACKGROUND AND PURPOSE: Magnetic resonance (MR) imaging is superior to computed tomography (CT) in radiotherapy of brain tumours. In this study an open low-field MR-simulator is evaluated in order to eliminate the cost of and time spent on additional CT scanning. MATERIALS AND METHODS: Eleven patients with brain tumours are both CT and MR scanned and the defined tumour volumes are compared. Image distortions and dose calculations based on CT density correction, MR unit density and MR bulk density, bone segmentation are performed. Monte Carlo simulations using 4 and 8 MV beams on homogeneous and bone segmented mediums are performed. RESULTS: Mean MR and CT tumour volumes of approximately the same size (V MR =55+/-34 cm3 and V CT =51+/-32 cm3) are observed, but for individual patients, small intersection volumes are observed. The MR images show negligible distortion within radial distances below 12 cm (<1.5 mm). On unit density mediums, dose errors above 2% are observed in low dose areas. Monte Carlo simulations with 4 MV photons show large deviations in dose (>2%) just behind the skull if bone is not segmented. CONCLUSIONS: It is feasible to use an MR-simulator for radiotherapy planning of brain tumours if bone is segmented or a careful choice of beam energy (>4 MV) is selected.     

Radiotherapy treatment planning of prostate cancer using magnetic resonance imaging alone.

PURPOSE: Accurate anatomical delineation of the gross tumour volume (GTV) is crucial for effective radiotherapy (RT) treatment of prostate cancers. Although reference to pelvic magnetic resonance (MR) for improved delineation of the prostate is a regular practice in some clinics, MR has not replaced CT due to its geometrical distortions and lack of electron-density information. The possibility and practicality of using MR only for RT treatment planning were studied. MATERIALS AND METHODS: The addition of electron-density information to MR images for conformal radiotherapy (CRT) planning of the prostate was quantified by comparing dose distributions created on the homogeneous density- and bulk-density assigned images to original CT for four patients. To quantify the MR geometrical distortions measurements of a phantom imaged in CT (Siemens Somatom Plus 4) and FLASH 3D T1-weighted MR (1.5 T whole body Siemens Magnetom Vision) were compared. Dose statistics from CRT treatment plans made on CT and MR for five patient data were compared to determine if MR-only treatment plans can be made. RESULTS: The differences between dose-plans on bulk-density assigned images when compared to CT were less than 2% when water and bone values were assigned. Dose differences greater than 2% were observed when images of homogeneous-density assignment were compared to the CT. Phantom measurements showed that the distortions in the FLASH 3D T1-weighted MR averaged 2 mm in the volume of interest for prostate RT planning. For the CT and MR prostate planning study, doses delivered to the planning target volume (PTV) in CT and MR were always inside a 93-107% dose range normalised to the isocentre. Also, the doses to the organs-at-risk in the MR images were similar to the doses delivered to the volumes in the registered CT image when the organ volumes between the two images were similar. CONCLUSIONS: Negligible differences were observed in dose distribution between CRT plans using bone+water CT number bulk-assigned image and original CT. Also, the MR distortions were reduced to negligible amounts using large bandwidth MR sequence for prostate CRT planning. MR treatment planning was demonstrated using a large bandwidth sequence and bulk-assigned images. The development of higher quality, low distortion MR sequence will allow regular practice of this technique.     

Study on dosimetric changes between initial and second treatment plans in IMRT for large volume NSCLC

Objective To evaluate the cumulative dose of the target volume and organs at risk (OARs) in intensity-modulated radiation therapy (IMRT) for large volume non-small cell lung cancer (NSCLC) based on rigid and deformation registration methods. The dosimetric changes between the initial and second treatment plans were compared. Methods Thirty patients treated with IMRT for large volume NSCLC with twice 4DCT scans acquired before radiotherapy and after 20 fractions of radiotherapy were recruited. The initial treatment plan (Plan1) based on the average density projection CT (CT1-avg) of the first 4DCT images and the second treatment plan (Plan2) based on the average density projection CT (CT2-avg) of the second 4DCT images were calculated. Then, the dose distributions of Plan1 and Plan2 were accumulated based on rigid and deformation registration methods to obtain Planrig and Plandef, respectively. Finally, the volume changes of gross tumor volume (GTV) and OARs between two CT scans were compared. The dose-volume parameters between Plan1 and other plans (including Plan2, Planrig and Plandef) were also statistically compared. Results Compared with the initial CT scan, the mean volume of GTV and heart on the second CT was decreased by 44.2% and 5.5%, respectively, while the mean volume of ipsilateral lung, contralateral lung and total lung was increased by 5.2%, 6.2% and 5.8%, respectively (all P<0.05). Compared with Plan1, the D95%, D98% and V100% of target volume IGTV (GTV fusion of 10 4DCT phases) and PTV in Plan2 did not significantly change (all P>0.05), and those in Planrig and Plandef were decreased (all P<0.05). The dose-volume parameters of spinal-cord, heart, ipsilateral lung and total lung in Plan2, Planrig and Plandef were significantly lower than those in Plan1(all P<0.05). Among them, the V30Gy and Dmean of heart were decreased by 27.3%, 16.5%, 15.3% and 15.2%, 6.6%, 5.6%, respectively. The V20Gy and Dmean of total lung were decreased by 15.6%, 4.5%, 3.7% and 15.7%, 6.2%, 5.1%, respectively. Some dose-volume parameters (including D95% and D98% of target volume, V40Gy of heart, V20Gy and Dmean of the ipsilateral lung and the total lung) of Plandef were higher than those in Planrig (all P<0.05). The Dice similarity coefficients (DSCs) of OARs after deformation registration were significantly higher than those after rigid registration (P<0.05). Conclusions The dose-volume parameters of OARs significantly differ between Plan1 and Plan2. Hence, all these parameters have a large degree of deviation in predicting radiation-induced injury of OARs. Nevertheless, the dose-volume parameters obtained by deformation registration can enhance the prediction accuracy.