Monaco与Pinnacle计划系统在肺癌容积旋转调强计划中的比较

目的 比较Monaco和Pinnacle 2套计划系统设计的肺癌容积旋转调强(VMAT)计划的计划质量、治疗效率和剂量验证精度.方法 选取20例肺癌病例,其中左肺癌10例,右肺癌10例,分别利用Monaco 3.0和Pinnacle 9.2两套计划系统设计VMAT计划,比较2种计划的靶区适形度、均匀性、最大剂量(D_max)、平均剂量(D_mean)与最小剂量(D_min)及危及器官的受照剂量;比较治疗计划执行时间、机器跳数和剂量验证的准确性.结果 除PTV的D_min外,Monaco计划靶区的其他各项剂量学指标都明显优于Pinnacle(t=5.927~12.034,P<0.05);2种计划除患侧肺V₁₀、全肺V₅外,Monaco计划肺的其他剂量学指标都差于Pinnacle(t=3.545~7.485,P<0.05),Monaco计划对心脏的保护明显优于Pinnacle(t=2.836~4.011,P<0.05),但较差的是Monaco计划执行时间(t=9.780,P<0.05)和MU数量(t=5.304,P<0.05).Monaco计划的Delta⁴验证结果优于Pinnacle(t=4.937,P<0.05).结论 对于肺癌的VMAT计划,Monaco与 Pinnacle两套计划系统都能满足临床应用要求;Pinnacle在肺的保护与计划执行方面有明显的优势,Monaco在靶区剂量分布和心脏的保护,以及剂量验证方面具有优势.     

乳腺癌根治术后双弧VMAT与IMRT计划的剂量学比较

目的 比较乳腺癌根治术后双弧的容积旋转调强放射治疗(VMAT)与5野的静态调强放射治疗(IMRT)2种计划之间的剂量学差异,评估VMAT技术在乳腺癌根治术后的剂量学特点与应用能力.方法 选取28例乳腺癌根治术后患者(左侧10例,右侧18例),分别制定双90度弧段的VMAT与5野的IMRT 2种计划,主要的计划评估参数为靶区的肿瘤控制概率(TCP)、适形指数(CI)、均匀指数(HI)以及接受相应处方剂量水平照射体积百分比V₉₅、V₁₁₀,危及器官(OAR)评估包括患侧肺的正常组织并发症概率(NTCP)、D_mean、V₅、V₂₀、V₃₀,心脏的NTCP值、D_mean、V₂₅,健侧乳腺的D_mean、机器跳数(MU)以及治疗时间.结果 VMAT计划与IMRT计划的TCP值分别为(96±2)%、(90±2)%(t=-6.28,P<0.01);HI值分别为0.15±0.04,0.22±0.02(t=13.29,P<0.05);肿瘤位于左侧时,心脏NTCP值在VMAT计划与IMRT计划中分别为(1.0±0.12)%,(1.7±0.13)%(t=2.14,P<0.05);肿瘤位于右侧时,2种计划心脏的NTCP差异无统计学意义,平均剂量分别为(3.27±0.26)、(6.0±0.47)Gy(t=9.21, P<0.01);VMAT计划在MU少于IMRT计划(t=9.58,P<0.01),治疗时间短于IMRT计划(t=8.40,P<0.05).结论 乳腺癌根治术后,VMAT计划具有更强的临床应用能力,且表现出更优的剂量学特点.     

乳腺癌保乳术后部分乳腺三种放疗计划的剂量学比较

目的 比较容积弧形调强（VMAT）、固定野动态调强（IMRT）及三维适形放疗（3D-CRT）技术对乳腺癌保乳术后采用部分乳腺放疗的剂量学差异。方法 选取20例临床分期为T_1-2N₀M₀的早期乳腺癌保乳术后患者进行VMAT,并同时设计IMRT及3D-CRT,比较3种计划的剂量学参数,包括剂量-体积直方图（DVH）、靶区剂量适形度、靶区及危及器官的剂量、机器跳数及治疗时间。结果 IMRT及VMAT计划靶区剂量分布优于3D-CRT计划,其中最大剂量,平均剂量及适形指数（CI）组间比较差异具有统计学意义（F=14.86、8.57、18.23,P<0.05）。正常组织受量：VMAT计划在患侧乳腺V₅上优于IMRT及3D-CRT计划（F=5.83,P<0.05）;IMRT在患侧肺V₂₀、V₅及D₅上有优势（F=16.39、3.62、4.81,P<0.05）;在对侧肺的统计中,IMRT计划在最大剂量及D₅上可以得到比VMAT和3D-CRT更低的剂量（F=3.99、3.43,P<0.05）;VMAT、3D-CRT和IMRT计划所需机器跳数值分别为621.0±111.9、707.3±130.9、1161.4±315.6,计划间的差异有统计学意义（F=31.30,P<0.05）。VMAT、3D-CRT和IMRT计划所需治疗时间分别为（1.5±0.2）、（7.0±1.6）、（11.5±1.9）min。结论 IMRT和VMAT计划靶区剂量分布优于3D-CRT计划,而不提高患侧肺剂量。对于部分乳腺癌的放疗,容积弧形调强放疗在降低机器跳数和减少治疗时间方面具有明显优势。     

胸上段食管癌断层定野与断层螺旋放疗和容积旋转调强放疗的剂量学比较

目的 比较胸上段食管癌断层定野放疗（TD）、断层螺旋放疗（HT）和容积旋转调强放疗（VMAT）的剂量学差异,为临床上食管癌放疗方式的选择提供依据。方法 选取15例临床分期为cT_2~4N_0~1M₀的胸上段食管癌患者,分别设计TD、HT和VMAT 3种计划。比较靶区的剂量体积直方图（DVH）、均匀指数（HI）、适形指数（CI）、危及器官（OAR）受量、治疗时间和机器跳数（MU）的差异。结果 HT和TD计划的D₂和D_mean均明显低于VMAT计划;TD计划的D₉₈和HT相似,但均高于VMAT计划。对于HI,HT < TD < VMAT,3组之间差异有统计学意义（F=81.603,P < 0.05）。3组计划的CI差异无统计学意义（P>0.05）。双肺的V₁₅,HT明显高于VMAT和TD （t=3.547、-2.626,P < 0.05）。TD计划的V₂₀与HT计划的相似,但高于VMAT计划（t=2.824、3.052, P < 0.05）。3组计划中的脊髓D_max无明显差异。HT和TD的执行时间、MU均高于VMAT,差异具有统计学意义（t=21.617、15.693、10.018、7.802,P < 0.05）。结论 与VMAT相比,HT和TD计划可明显改善胸上段食管癌靶区的剂量分布,可获得更好的适形度。但VMAT比HT或TD明显降低双肺V₂₀、MU及治疗时间。TD与HT相比,HT的靶区剂量分布更好,但TD降低了双肺的V₁₅,且缩短治疗时间。     

MdaccAutoPlan软件在鼻咽癌调强放疗计划设计的应用分析

目的 比较MdaccAutoPlan软件与人工计划设计在鼻咽癌调强放疗的应用价值。方法 选取20例鼻咽癌初治患者,应用MdaccAutoPlan软件设计自动治疗计划（MDAP）与人工计划,在保证射野角度、优化参数、计划要求等条件尽量一致的情况下,对两种计划进行计划评价剂量学以及工作效率方面数据的对比。结果 MDAP中PGTV、PTV1、PTV2的D_98%、D_mean较人工计划降低2.5%、0.3%、0.1%、0.5%、0.6%、1.0%,PGTV、PTV1、PTV2的D_2%较人工计划上升1.7%、1.5%、0.6%。其中PGTV D_98%、PGTV D_2%和PTV2 D_98%两组比较,差异有统计学差异（t=5.519、6.701、0.937,P<0.05）。MDAP的右侧腮腺D_50%、左侧腮腺D_50%、脊髓D_max、脊髓D_mean较人工计划减少24.8%、27.7%、11.4%、14.0%,两组比较,差异有统计学意义（t=5.447、5.375、6.786、3.810,P<0.05）,两侧眼晶状体较人工计划升高65.0%、19.3%,两组比较差异有统计学意义（t=9.863、3.440,P<0.05）。视神经、视交叉和脑干3种危及器官的剂量学比较,差异均无统计学意义（P>0.05）。MDAP的后颈部剂量分布略优于人工计划,剂量体积直方图（DVH）中,人工计划的计划靶区曲线、脑干曲线、脊髓曲线均高于MDAP。MDAP计划的人工操作时间较人工计划减少了59.4%,计算机处理时间较人工计划增加了34.4%。结论 MdaccAutoPlan软件对鼻咽癌放射治疗有一定的临床应用价值,危及器官剂量限制可能优于人工计划,且能减少计划设计时间,提高计划效率。     

螺旋断层放疗在同时性双侧乳腺癌中的应用研究

目的 研究螺旋断层放疗(helical tomotherapy,HT)与容积旋转调强放疗(volumetric modulated arc therapy,VMAT)在同时性双侧乳腺癌术后放疗中的剂量学、治疗出束时间差异,探讨HT技术的临床应用可行性。方法 回顾性分析并选取2017年2月至2022年5月于广西医科大学第四附属医院行改良根治术后放疗的9例同时性双侧乳腺癌患者为研究对象,对每例患者分别使用Precision计划系统制定HT计划和RayStation计划系统制定VMAT计划。所得所有计划按照计划类型分为HT组和VMAT组。采用配对样本t检验比较两种放疗技术的靶区和危及器官(organ at risk,OAR)的剂量学参数及治疗出束时间。结果 两组计划均能满足临床治疗要求。HT组的靶区覆盖度(D_95%和V_100%)、适形指数CI、平均剂量D_mean和中位剂量D_50%均优于VMAT组,差异均有统计学意义(t=-3.21、-3.39、-5.03、3.76、4.97,P < 0.05);两组计划的靶区最大剂量D_2%、最小剂量D_98%、高剂量体积V_107%和V_110%、均匀性指数HI的差异无统计学意义(P > 0.05)。OAR方面,HT组的双肺V₂₀、D_mean均明显低于VMAT组,但双肺V₅明显高于VMAT组,差异均有统计学意义(t=-3.01、3.83、-2.81,P < 0.05);同时HT组明显降低了心脏的V₂₀、V₃₀、V₄₀、D_mean以及肝脏的V₂₀、D_mean,差异均有统计学意义(t=3.76、-2.83、-2.74、5.93、4.57、4.48,P < 0.05);其他OAR脊髓、甲状腺、肱骨头的受照剂量差异无统计学意义(P > 0.05)。HT组的治疗出束时间显著高于VMAT组(t=11.32,P < 0.05)。结论 与VMAT相比,HT具备更大的剂量学优势,能提供更优的靶区覆盖度、适形度和平均剂量,且可明显降低OAR双肺、心脏和肝脏的整体受照剂量,但双肺的低剂量区V₅、治疗时间多于VMAT,不过仍满足临床治疗需求,故可考虑将HT技术应用于同时性双侧乳腺癌的改良根治术后放疗。     

基于计划质量度量(PQM)量化比较有无均整器模式下肝癌容积旋转调强放疗计划

目的 通过建立计划质量度量（PQM）量化评估肝癌放疗计划中常规分割的容积旋转调强放疗（VMAT）在有无均整器模式下的计划质量。方法 选取10例肝癌患者,分别在6 MV X射线的传统均整器（FF）模式和无均整器（FFF）模式下进行计划设计,评价靶区（PTV）和危及器官（OAR）的剂量分布,比较两种模式下加速器的机器跳数和出束时间。根据临床的限量要求定义具有16个评价对象的计划质量度量来评估两种模式下的计划质量。结果 FFF模式下,靶区最大剂量小于FF模式（t=3.828,P<0.05）,正常肝组织的超过5 Gy归一化体积（V₅）和平均剂量（D_mean）低于FF模式（t=2.716、3.007,P<0.05）。FFF模式的平均机器跳数（574±130）MU比FF模式（518±81）MU高（t=-2.782,P<0.05）,而平均出束时间（108±36）s相比FF模式（160±29）s明显降低（t=6.767,P<0.05）。FFF模式的整体PQM评分值高于FF模式（t=-2.746,P<0.05）。结论 FFF模式能够更好的保护危及器官的低剂量区域。FFF模式的机器跳数高,但是出束时间明显低于FF模式。参照PQM评估标准,FFF模式的整体计划质量略高。     

乳腺癌根治术后调强放疗的一体化射野设计

目的 比较一种一体化调强射野设计方式与常规射野设计方法在乳腺癌根治术后调强放疗中的剂量学差异。方法 选取41例左侧乳腺癌根治术后患者的CT图像,进行胸壁、部分腋窝、锁骨上、内乳等靶区及危及器官（OAR）勾画。对每一套CT图像分别制作一体化射野设计的调强计划和常规调强计划。评估两种计划靶区和OAR剂量学分布。结果 两种计划靶区剂量分布和OAR受照剂量均满足临床要求,靶区剂量学参数差异无统计学意义（P>0.05）。一体化调强计划相比于常规计划：患侧肺V₅降低9.7%（t=2.407,P<0.05）、V₁₀降低11.2%（t=2.160,P<0.05）、V₂₀降低17.3%（t=2.465,P<0.05）、V₃₀降低13.4%（t=2.119,P<0.05）、D_mean降低13.8%（t=2.258,P<0.05）;心脏V₃₀下降28.4%（t=2.589,P<0.05）、D_mean下降23.2%（t=2.409,P<0.05）;其他OAR剂量学差异不具有统计学意义（P>0.05）。结论 一体化调强射野设计技术显著降低了患侧肺和心脏的受照体积与受照剂量,有望减轻乳腺癌根治术后放疗的不良反应。新型设计方案选取了较多的样本,包含不同分期的左乳癌根治术患者,对乳腺癌根治术后调强放疗临床应用具有普遍性,可以作为一种新的照射方式推广。     

胸上段食管癌无均整器容积弧形调强与固定野调强放疗计划的剂量学比较

目的 探讨在瓦里安TrueBeam^TM直线加速器中使用无均整器出束容积弧形调强(RA-FFF)及常规固定野调强(IMRT)两种计划剂量学差异.方法 选择10例分期为cT_2-3N_0-1M_0-1a胸上段食管癌患者定位CT资料,使用ECLIPSE^TM 10.0.4治疗计划系统分别设计RA-FFF、IMRT根治性放疗计划,处方剂量为60 Gy/30次,比较2种计划的剂量学参数和执行效率.结果 2种计划靶区适形度相似,差异无统计学意义;IMRT计划的均匀性指数高于RA-FFF计划(t=7.298,P=0.008);RA-FFF计划中肺组织的V₂₀、V₅低于IMRT计划(t=2.451、2.604,P<0.05).RA-FFF及IMRT两种计划制定时间分别为(5.3±1.4)、(3.5±1.7)h(t=2.585,P<0.05),机器总跳数分别为632±213及734±132(t=-1.287,P=0.084),治疗执行时间分别为(2.2±0.9)、(4.5±1.3)min(t=4.60,P<0.01).结论 与IMRT计划相比,RA-FFF在胸上段食管癌治疗中具有相似的靶区剂量分布,可更好地保护肺组织,计划制定时间较长但执行效率较高.     

半铅门技术在口咽癌调强治疗计划中的剂量学研究

目的 研究半铅门容积旋转调强计划（H-VMAT）应用于口咽癌时的剂量优势,与全铅门容积旋转调强计划（W-VMAT）,固定野调强计划（IMRT）进行比较。方法 选取10例口咽癌患者CT图像传至Eclipse11.0（美国Varian公司）治疗计划系统行H-VMAT、W-VMAT和IMRT。两种VMAT计划均采用双弧360℃照射,IMRT计划采用7野均分。3种调强计划的通量优化条件一样。统计靶区PGTV、PCTV1、PCTV2、PGTVln、PCTVln的D₂、D₉₈、D₅₀、均匀性指数（HI）、适形指数（CI）;脑干、脊髓的D_{1 cc};腮腺、口腔、喉的平均剂量D_mean,颈部正常组织D_mean,跳数（MU）以及其他剂量学参数。结果 3种调强计划方式之间比较,H-VAMT计划改善了靶区的HI、CI（靶区PCTV2除外）,差异具有统计学意义（HI：F=3.959、6.764、10.581、6.770、13.040,P<0.05;CI：F=6.594、4.138、0.842、4.031、5.388,P<0.05）,同时明显降低了脑干、脊髓的D_max（F=4.509、20.331,P<0.05）和D_{1 cc}（F=27.432、26.314,P<0.05）,减少了口腔、喉以及颈部正常组织的D_mean（F=4.279、29.498、19.295,P<0.05）,其中口腔、喉的V_50%在IMRT中略低（F=8.140,P<0.05）。IMRT对口腔、喉的保护略优于W-VMAT,但剂量分布最差。H-VMAT计划在颈部正常组织以及下颈,背部的剂量分布最优,IMRT则存在高剂量曲线。结论 口咽癌容积旋转调强计划采用半铅门技术优于全铅门W-VMAT、固定野IMRT计划,可以考虑临床实践。     

Volumetric Modulated Arc Therapy vs. IMRT for the Treatment of Distal Esophageal Cancer

Several studies have demonstrated that volumetric modulated arc therapy (VMAT) has the ability to reduce monitor units and treatment time when compared with intensity-modulated radiation therapy (IMRT). This study aims to demonstrate that VMAT is able to provide adequate organs at risk (OAR) sparing and planning target volume (PTV) coverage for adenocarcinoma of the distal esophagus while reducing monitor units and treatment time. Fourteen patients having been treated previously for esophageal cancer were planned using both VMAT and IMRT techniques. Dosimetric quality was evaluated based on doses to several OARs, as well as coverage of the PTV. Treatment times were assessed by recording the number of monitor units required for dose delivery. Body V₅ was also recorded to evaluate the increased volume of healthy tissue irradiated to low doses. Dosimetric differences in OAR sparing between VMAT and IMRT were comparable. PTV coverage was similar for the 2 techniques but it was found that IMRT was capable of delivering a slightly more homogenous dose distribution. Of the 14 patients, 12 were treated with a single arc and 2 were treated with a double arc. Single-arc plans reduced monitor units by 42% when compared with the IMRT plans. Double-arc plans reduced monitor units by 67% when compared with IMRT. The V₅ for the body was found to be 18% greater for VMAT than for IMRT. VMAT has the capability to decrease treatment times over IMRT while still providing similar OAR sparing and PTV coverage. Although there will be a smaller risk of patient movement during VMAT treatments, this advantage comes at the cost of delivering small doses to a greater volume of the patient.     

A class solution for volumetric-modulated arc therapy planning in postprostatectomy radiotherapy

This study is aimed to test a postprostatectomy volumetric-modulated arc therapy (VMAT) planning class solution. The solution applies to both the progressive resolution optimizer algorithm version 2 (PRO 2) and the algorithm version 3 (PRO 3), addressing the effect of an upgraded algorithm. A total of 10 radical postprostatectomy patients received 68 Gy to 95% of the planning target volume (PTV), which was planned using VMAT. Each case followed a set of planning instructions; including contouring, field setup, and predetermined optimization parameters. Each case was run through both algorithms only once, with no user interaction. Results were averaged and compared against Radiation Therapy Oncology Group (RTOG) 0534 end points. In addition, the clinical target volume (CTV) D₁₀₀, PTV D₉₉, and PTV mean doses were recorded, along with conformity indices (CIs) (95% and 98%) and the homogeneity index. All cases satisfied PTV D₉₅ of 68 Gy and a maximum dose < 74.8 Gy. The average result for the PTV D₉₉ was 64.1 Gy for PRO 2 and 62.1 Gy for PRO 3. The average PTV mean dose for PRO 2 was 71.4 Gy and 71.5 Gy for PRO 3. The CTV D₁₀₀ average dose was 67.7 and 68.0 Gy for PRO 2 and PRO 3, respectively. The mean homogeneity index for both algorithms was 0.08. The average 95% CI was 1.17 for PRO 2 and 1.19 for PRO 3. For 98%, the average results were 1.08 and 1.12 for PRO 2 and PRO 3, respectively. All cases for each algorithm met the RTOG organs at risk dose constraints. A successful class solution has been established for prostate bed VMAT radiotherapy regardless of the algorithm used.     

Volumetric-modulated arc radiotherapy for pancreatic malignancies: Dosimetric comparison with sliding-window intensity-modulated radiotherapy and 3-dimensional conformal radiotherapy

Volumetric-modulated arc radiotherapy (VMAT) is an iteration of intensity-modulated radiotherapy (IMRT), both of which deliver highly conformal dose distributions. Studies have shown the superiority of VMAT and IMRT in comparison with 3-dimensional conformal radiotherapy (3D-CRT) in planning target volume (PTV) coverage and organs-at-risk (OARs) sparing. This is the first study examining the benefits of VMAT in pancreatic cancer for doses more than 55.8 Gy. A planning study comparing 3D-CRT, IMRT, and VMAT was performed in 20 patients with pancreatic cancer. Treatments were planned for a 25-fraction delivery of 45 Gy to a large field followed by a reduced-volume 8-fraction external beam boost to 59.4 Gy in total. OARs and PTV doses, conformality index (CI) deviations from 1.0, monitor units (MUs) delivered, and isodose volumes were compared. IMRT and VMAT CI deviations from 1.0 for the large-field and the boost plans were equivalent (large field: 0.032 and 0.046, respectively; boost: 0.042 and 0.037, respectively; p > 0.05 for all comparisons). Both IMRT and VMAT CI deviations from 1.0 were statistically superior to 3D-CRT (large field: 0.217, boost: 0.177; p < 0.05 for all comparisons). VMAT showed reduction of the mean dose to the boost PTV (VMAT: 61.4 Gy, IMRT: 62.4 Gy, and 3D-CRT: 62.3 Gy; p < 0.05). The mean number of MUs per fraction was significantly lower for VMAT for both the large-field and the boost plans. VMAT delivery time was less than 3 minutes compared with 8 minutes for IMRT. Although no statistically significant dose reduction to the OARs was identified when comparing VMAT with IMRT, VMAT showed a reduction in the volumes of the 100% isodose line for the large-field plans. Dose escalation to 59.4 Gy in pancreatic cancer is dosimetrically feasible with shorter treatment times, fewer MUs delivered, and comparable CIs for VMAT when compared with IMRT.     

容积旋转调强计划计算分辨率对COMPASS验证通过率的影响

目的 研究容积旋转调强放疗（VMAT）计划设计采用不同计算分辨率对COMPASS验证通过率的影响。方法 选取10例宫颈癌术后患者,在治疗计划系统上采用4种计算分辨率0.2 cm×0.2 cm×0.2 cm、0.3 cm×0.3 cm×0.3 cm、0.4 cm×0.4 cm×0.4 cm、0.5 cm×0.5 cm×0.5 cm设计VMAT治疗计划。计划传至加速器上执行,由COMPASS实际测量重建并与TPS优化的剂量分布进行比较得到每个计划的偏差值,统计分析4种计划的偏差值是否有统计学意义。结果 肿瘤靶区的D_mean和D₉₅,COMPASS测量重建结果表明D_mean偏差值的平均值<0.5%,D₉₅<1.3%,标准差均<1.0%。对于4种计划危及器官（OAR）,其中左右股骨头的D_mean偏差值最大可达-6.7%、-7.0%、-8.0%、-5.8%,直肠V₃₅偏差值最大可达-4.9%、-6.3%、-6.1%、-5.7%,是OAR中相应参数偏差值最大的两个器官。肿瘤靶区的γ通过率都在95%以上,标准差不超过2.5%;OAR除了股骨头γ通过率略低,在95%以上,标准差1.9%~6.1%不等,其余都达到98%以上,标准差<2.5%,差异均无统计学意义（P>0.05）。平均γ值的分析结果与γ通过率相一致,除了股骨头的平均γ值>0.4外,PTV和其余OAR的平均γ值都<0.4,差异均无统计学意义（P>0.05）。结论 采用0.2~0.5 cm计算分辨率优化宫颈癌术后VMAT计划,不影响COMPASS验证通过率。     

Comparison of Prostate IMRT and VMAT Biologically Optimised Treatment Plans

Recently, a new radiotherapy delivery technique has become clinically available—volumetric modulated arc therapy (VMAT). VMAT is the delivery of IMRT while the gantry is in motion using dynamic leaf motion. The perceived benefit of VMAT over IMRT is a reduction in delivery time. In this study, VMAT was compared directly with IMRT for a series of prostate cases. For 10 patients, a biologically optimized seven-field IMRT plan was compared with a biologically optimized VMAT plan using the same planning objectives. The Pinnacle RTPS was used. The resultant target and organ-at-risk dose-volume histograms (DVHs) were compared. The normal tissue complication probability (NTCP) for the IMRT and VMAT plans was calculated for 3 model parameter sets. The delivery efficiency and time for the IMRT and VMAT plans was compared. The VMAT plans resulted in a statistically significant reduction in the rectal V25Gy parameter of 8.2% on average over the IMRT plans. For one of the NTCP parameter sets, the VMAT plans had a statistically significant lower rectal NTCP. These reductions in rectal dose were achieved using 18.6% fewer monitor units and a delivery time reduction of up to 69%. VMAT plans resulted in reductions in rectal doses for all 10 patients in the study. This was achieved with significant reductions in delivery time and monitor units. Given the target coverage was equivalent, the VMAT plans were superior.     

VMAT vs. 7-Field-IMRT: Assessing the Dosimetric Parameters of Prostate Cancer Treatment with a 292-Patient Sample

We compared normal tissue radiation dose for the treatment of prostate cancer using 2 different radiation therapy delivery methods: volumetric modulated arc therapy (VMAT) vs. fixed-field intensity-modulated radiation therapy (IMRT). Radiotherapy plans for 292 prostate cancer patients treated with VMAT to a total dose of 7740 cGy were analyzed retrospectively. Fixed-angle, 7-field IMRT plans were created using the same computed tomography datasets and contours. Radiation doses to the planning target volume (PTV) and organs at risk (bladder, rectum, penile bulb, and femoral heads) were measured, means were calculated for both treatment methods, and dose-volume comparisons were made with 2-tailed, paired t-tests. The mean dose to the bladder was lower with VMAT at all measured volumes: 5, 10, 15, 25, 35, and 50% (p < 0.05). The mean doses to 5 and 10% of the rectum, the high-dose regions, were lower with VMAT (p < 0.05). The mean dose to 15% of the rectal volume was not significantly different (p = 0.95). VMAT exposed larger rectal volumes (25, 35, and 50%) to more radiation than fixed-field IMRT (p < 0.05). Average mean dose to the penile bulb (p < 0.05) and mean dose to 10% of the femoral heads (p < 0.05) were lower with VMAT. VMAT therapy for prostate cancer has dosimetric advantages for critical structures, notably for high-dose regions compared with fixed-field IMRT, without compromising PTV coverage. This may translate into reduced acute and chronic toxicity.     

A volumetric approach to path-length measurements is essential when treating radiotherapy with modulated beams

The established dosimetric benefits of intensity-modulated radiation therapy (IMRT) and volumetric-modulated arc therapy have lead to their increased use in prostate radiotherapy. Complimenting these techniques, volumetric image guidance has supported increased positional accuracy. In addition, 3-dimensional image guidance has also allowed for assessment of potential dosimetric variation that can be attributed to a deformation of either internal or external structures, such as rectal distension or body contour. Compounding these issues is the variation of tissue density through which the new field position passes and also the variation of dose across a modulated beam. Despite the growing level of interest in this area, there are only a limited number of articles that examine the effect of a variation in beam path length, particularly across a modulated field. IMRT and volumetric-modulated radiation therapy (VMAT) fields are dynamic in nature, and the dose gradient within these fields is variable. Assessment of variation of path length away from the beam׳s central axis and across the entire field is vital where there is considerable variation of dose within the field, such as IMRT and VMAT. In these cases, reliance on the traditional central axis to focus skin distances is no longer appropriate. This article discusses these more subtle challenges that may have a significant clinical effect if left unrecognized and undervalued.     

A robust volumetric arc therapy planning approach for breast cancer involving the axillary nodes

We quantify the robustness of a proposed volumetric-modulated arc therapy (VMAT) planning and treatment technique for radiotherapy of breast cancer involving the axillary nodes. The proposed VMAT technique is expected to be more robust to breast shape changes and setup errors, yet maintain the improved conformity of VMAT compared to our current standard technique that uses tangential intensity-modulated radiation therapy (IMRT) fields. Treatment plans were created for 10 patients. To account for anatomical variation, planning was carried out on a computed tomography (CT) with an expanded breast, followed by segment weight optimization (SWO) on the original planning CT (VMAT + SWO). For comparison purposes, tangential field IMRT plans and conventional VMAT (cVMAT) plans were also created. Anatomical changes (expansion and contraction of the breast) and setup errors were simulated to quantify changes in target coverage, target maximum, and organ-at-risk (OAR) doses. Finally, robustness was assessed by calculating the actual delivered dose for each fraction using cone-beam CT images acquired during treatment. Target coverage of VMAT + SWO was shown to be significantly more robust compared to cVMAT technique, against anatomical variations and setup errors. Sensitivity of the clinical target volume (CTV) V95% is ?5%/cm of expansion for the proposed technique, which is identical to the IMRT technique and much lower than the ?22%/cm for cVMAT. Results are similar for setup errors. OAR doses are mostly insensitive to anatomical variations and the OAR sensitivity to setup variations does not depend on the planning technique. The results are confirmed by dose distributions recalculated on cone-beam CT, showing that for VMAT + SWO the CTV V95% remains within 2.5% of the planned value, whereas it deviates by up to 7% for cVMAT. A practical VMAT planning technique is developed, which is robust to daily anatomical variations and setup errors.