瓦里安Portal Dosimetry和PTW 1500矩阵在HalcyonTM治疗计划剂量验证的对比研究

目的 比较Portal Dosimetry（PD）和PTW OCTAVIUS 1500矩阵结合Octagonal模体（Oct1500）两种剂量验证方式在Halcyon^TM加速器治疗计划剂量验证中的表现。方法 选取在Halcyon^TM做临床试验的20例入组患者,包括22个IMRT/VMAT治疗计划和74个辐射野,分别采用两种验证方式和多种γ 2D评估策略进行剂量验证,对比验证方式及评估策略之间的验证结果,为Halcyon^TM治疗计划验证方式和评价策略的选择提供数据支持。结果 Oct1500方式74个辐射野和22个治疗计划γ 2D通过率分别为95.26±3.59、95.01±3.62（局部剂量）、99.05±1.35、98.57±1.96（最大剂量）,两种评估策略之间差异有统计学意义（Z=-7.220、-4.108,P<0.05）;PD方式为84.11±1.35（1 mm/1%）、99.07±1.35（2 mm/2%）、99.86±1.35（3 mm/3%）,3种评估策略之间差异有统计学意义（Z=-7.475、-7.475、-6.906,P<0.05）;74个辐射野全局剂量、3 mm/3%的评价策略两种验证方式之间差异有统计学意义（Z=-5.072,P<0.05）。结论 两种剂量验证方式均可用于Halcyon^TM治疗计划剂量验证;PD方式在验证效率和由空间分辨率所致的剂量验证精度方面优于Oct1500。推荐使用2 mm/2%（PD）和全局剂量、3 mm/3%（Oct1500）评估策略。     

立体定向调强放射治疗剂量验证结果分析

目的 研究测量数据插值、计划系统剂量计算网格及剂量评估阈值等因素对立体定向调强放射治疗患者计划的剂量验证结果的影响。方法 回顾性分析了50例立体定向放射治疗的患者放疗计划的剂量验证结果。剂量验证设备采用MatriXX及配套MultiCube固体水模。测量数据分别选择线性插值（1.00 mm）和不插值（7.62 mm）两种分辨率;计划系统剂量计算网格分别选择1.0、2.5和4.0 mm;剂量评估阈值分别选择10%、20%和30%,γ评估标准分别选择2%/2 mm、3%/2 mm和3%/3 mm,分析不同因素选择对平面剂量验证结果的影响。结果 测量数据插值选择线性插值和不插值,2%/2 mm标准下,γ平均通过率分别为（86.3±7.3）%和（93.7±5.5）%;3%/2 mm标准下,γ平均通过率分别为（94.1±4.4）%和（97.7±3.9）%;3%/3 mm标准下,γ平均通过率分别为（97.7 ±2.2）%和（99.1±1.7）%。相比1.0 mm的剂量计算网格,使用2.5 mm计算网格,3种标准下γ平均通过率分别降低3.8%、1.9%和0.8%（t=8.41、9.06、5.30,P<0.05）,4.0 mm分别降低6.5%、6.0%和3.5%（t=-13.76、-13.15、-9.80,P<0.05）,差异有统计学意义。相比剂量评估阈值为10%,当阈值设置为20%时,2%/2 mm、3%/2 mm和3%/3 mm标准下,γ平均通过率分别降低2.4%、1.0%和0.6%（t=-8.60、-5.86、-4.68,P<0.05）;当阈值设置为30%,3种标准下γ平均通过率分别降低4.0%、1.7%和0.9%（t=-9.45、-6.66、-5.06,P<0.05）,差异有统计学意义。结论 测量数据插值、剂量计算网格大小及剂量评估阈值对立体定向放射治疗患者计划剂量验证结果均有明显影响,因此在进行立体定向放射治疗患者计划剂量验证时需要考虑这些因素。     

三种验证设备在立体定向放射治疗的剂量验证结果分析

目的 比较靶区体积、计算网格和剂量阈值等参数对ArcCHECK、SRS MapCHECK和3DMap 3种验证设备的立体定向放射治疗剂量验证结果的影响。方法 选取50例立体定向放疗计划,分别比较靶区体积(<25 cm³和≥25 cm³)、计算网格(1.0、1.5和2.0 mm)和剂量阈值(5%、10%和15%)对3种验证设备3 mm/3%、3 mm/2%、3 mm/1%、2 mm/3%和 2 mm/2%的γ通过率的影响。结果 靶区体积的改变对于3DMap的影响较大,与小体积相比,3DMap大体积的3 mm/3%、3 mm/2%、2 mm/3%和2 mm/2%的γ通过率分别增加2.2%、2.2%、4.4%和4.7%(t=-2.76、-2.17、-4.72、-3.86,P<0.05);计算网格1.5和1.0 mm相比,对于MapCHECK的影响较大,5种γ通过率分别降低0.7%、1.1%、1.7%、0.9%和1.5%(t=-6.15、 -6.23、-5.98、-5.11、-8.34,P<0.05)。计算网格2.0和1.0 mm相比,对于ArcCHECK影响较大,5种γ通过率分别降低1.0%、1.7%、2.4%、1.7%和2.7%(t=-4.75、-7.30、 -8.63、 -7.11、-8.26,P<0.05);剂量阈值10%和5%相比,对于ArcCHECK影响较大,3 mm/3%、 3 mm/2%、2 mm/3%和2 mm/2%的γ通过率分别降低0.5%、0.8%、1.2%和1.7% (t=5.20、5.68、8.17、9.99,P<0.05)。剂量阈值15%和5%相比,对于3DMap的影响较大,3 mm/3%、 3 mm/2%、2 mm/3%和2 mm/2%的γ通过率分别降低1.6%、1.7%、2.8%和3.2%(t=3.25、2.98、4.40、4.21,P<0.05)。结论 靶区体积、计算网格和剂量阈值对3种验证设备立体定向放疗计划的验证通过率产生不同程度的影响。在临床使用时应对于不同的验证设备具体考虑这些参数对于验证结果的影响。     

调强放疗三维剂量验证系统精度测试及临床应用研究

目的 测试三维剂量验证系统Compass^R测量重建及独立计算剂量的精度,评估其临床应用可行性。方法 设计一系列宽度分别为2、1、0.5 cm的条纹状射野,并选取11例肺部调强放疗（IMRT）计划,使用胶片和电离室对被测系统的平面剂量分布和特定点绝对剂量进行验证测试;使用Compass^R对IMRT模体计划做基于解剖信息的三维剂量验证,验证体积γ通过率、平均剂量偏差等参数。结果 条纹状射野测试,与胶片测量相比,被测系统重建和计算剂量γ通过率大于90%（选用3%/3 mm、2%/2 mm标准）,宽度为0.5 cm射野在半影区内γ通过率略差,被测系统重建和计算剂量曲线与胶片测量的曲线最大偏离分别3.21%和2.70%;IMRT计划特定点绝对剂量偏差在3%以内,最大偏差发生在肺部,IMRT计划等中心平面测量重建与胶片测量的γ通过率平均为（94.65±1.93）% （选用3%/3 mm标准）;三维剂量验证结果,靶区及危及器官的体积γ通过率均大于90%,平均剂量的偏差<1%。结论 测试系统剂量精度可满足IMRT计划验证要求,并能给出与患者解剖结构相关的体积剂量误差与位置误差的信息,有利于评估其对临床的影响。     

立体定向放疗计划验证模体在脑转移瘤HyperArc技术中的应用研究

目的 探究StereoPhan(SP)模体与SRS MapCHECK(SMC)半导体矩阵用于脑转移瘤患者HyperArc(HA)计划剂量验证的可行性。方法 选取16例在北京协和医院接受HA放射治疗的脑转移瘤患者为研究对象,分别将电离室和SMC半导体矩阵插入SP模体,测量患者的HA验证计划的点剂量与平面剂量,并与治疗计划系统(TPS)计算数据对比,平面剂量的γ分析标准取2 mm/3%、2 mm/2%、1 mm/3%和1 mm/2%。结果 16例患者的点剂量平均偏差是1.33%±0.84%,平面剂量γ通过率在2 mm/3%、2 mm/2%的标准下依次为99.72%±0.46%、98.93%±1.32%,在 1 mm/3% 、1 mm/2%的标准下依次为98.85%±1.79%、97.13%±3.19%。结论 SP模体与SMC半导体矩阵适合用于开展脑转移瘤患者HA计划的剂量验证工作,在进行点剂量和平面剂量验证时,可以分别采用3%和1mm/2%的分析标准。     

瓦里安呼吸门控实时位置管理系统对放射治疗计划剂量学的影响

目的 研究瓦里安呼吸门控实时位置管理(RPM)系统对放射治疗计划剂量学的影响。方法 回顾性选取40例胸腹部肿瘤放疗计划,采用质量控制运动模体产生呼吸门控信号,选取呼气末30%~60%稳定时相作为呼吸门控窗,在Edge加速器RPM呼吸门控模式下对上述计划进行Portal Dosimetry(PD)系统剂量验证,采用不同的γ通过率标准进行剂量分析,并分析其γ值的分布特点,与非门控模式下验证结果进行对比。结果 在RPM呼吸门控模式下,对于不同均整器模式下的调强放射治疗计划(IMRT)或容积调强放射治疗计划(VMAT),采用γ(3%,3 mm)或(3%,2 mm)标准,所有计划通过率均在95.5%以上,采用更严格的γ(2%,2 mm)标准,所有计划通过率均在90%以上,符合美国医学物理师学会(AAPM)推荐的临床治疗标准。非门控模式下剂量验证结果通过率略优于呼吸门控模式下验证结果,两种模式下差异具有统计学意义(3%/3 mm,Z=-1.45;3%/2 mm,Z=-2.86;2%/2 mm,Z=-3.70;1%/1 mm,Z=-4.52, P<0.05)。两种模式下计划验证结果γ值的最小值、最大值及γ＞1.5的份额差异不明显,但非门控模式下γ的平均值及标准偏差总体更小。结论 RPM呼吸门控技术引入带来的剂量影响在临床可接受范围内,该门控模式下计划执行是安全可靠的。     

2 010例调强放疗患者计划剂量验证结果分析

目的 分析2 010例调强放疗计划剂量验证结果,为改进和完善调强放疗计划验证方法提供参考。方法 回顾性分析北京大学第三医院2012年2月—2016年2月美国瓦里安公司Trilogy加速器治疗的2 010例计划的剂量验证结果,其中调强放射治疗（IMRT）计划965例,容积旋转调强放疗（VMAT）计划1 045例。计划设计使用Eclipse计划系统,剂量验证采用MatriXX及Multicube模体。分析计划和测量等中心点剂量差异,3%/3 mm标准平面剂量分布的γ通过率。等中心点剂量差异<±3%定为通过,平面剂量分布γ通过率>90%定为通过。分析病变部位、治疗技术（IMRT和VMAT）对计划验证通过率的影响。结果 2 010例计划等中心点剂量平均差异为-0.3%±2.4%,γ通过率为97.9%±3.4%。88.2%和96.7%的计划能够通过点剂量验证和平面剂量验证标准。不同病变部位计划验证γ通过率不同（F=3.09,P<0.05）。不同病变计划点剂量和面剂量验证通过率不同（χ²=40.93、39.15,P<0.05）。IMRT和VMAT计划验证点剂量通过率和面剂量验证通过率差异均无统计学意义（P>0.05）。结论 大部分调强放疗计划能够通过计划验证,不同病变部位计划验证通过率不同,IMRT和VMAT计划验证通过率无差异。     

基于盆腔迭代锥形束CT图像的剂量学可行性分析

目的 研究利用盆腔迭代锥形束CT（CBCT）图像用于治疗计划剂量计算的可行性分析，为自适应放疗提供图像保障。方法 使用Varian Halcyon 2.0环形加速器对CIRS 062 M模体（CIRS，Norfolk，VA，USA）进行扫描，测量其不同散射条件下的CT值并计算其平均值，建立锥形束CT-电子密度转换曲线（iterative Cone-beam CT to electron density，ICBCT-ED）。采集CIRS 002PRA盆腔调强专用模体的CT和不同位置的ICBCT图像，设计基于CT图像的VMAT计划，移植至ICBCT图像上，重新进行剂量计算，比较靶区、危及器官及三维体积剂量γ通过率的差异。以患者实际治疗计划为基准，回顾性分析10例盆腔患者全流程三维剂量γ通过率的差异。结果 无散射体的孤立模式与全散射中心位置的CT值偏差较大，最大偏差144 HU。其他全散射位置与中心位置CT值相近，最大偏差<50 HU。基于盆腔模体不同位置处的ICBCT图像的计算结果，无论靶区还是危及器官的剂量偏差均<1 Gy。与基于CT图像的计划相比，基于ICBCT图像的三维剂量γ通过率1%/1 mm和2%/2 mm的平均值分别为（88.86±1.18）%和（98.38±0.89）%。10例盆腔肿瘤患者2%/2 mm和3%/3 mm的平均值范围分别为90.03%~95.43%和93.58%~97.78%。最差结果为膀胱过充盈引起的外轮廓变化造成的剂量差异，2%/2 mm和3%/3 mm的三维剂量通过率仅为85.90%和92.90%。结论 在足够的散射条件下，重建ICBCT-ED转换曲线，利用Halcyon直线加速器的ICBCT图像进行治疗计划设计，其精度是可以满足临床应用的标准的，为将来的自适应放疗提供了保障。     

呼吸运动状态对动态调强放疗剂量分布影响的研究

目的 探讨不同幅度、周期、方向的呼吸运动对动态调强放疗（IMRT）计划中靶区剂量分布的影响。方法 选取30例肺癌病例,按靶区体积大小分为A（72.0~200.2 cm³）、B（271.7~380.0 cm³）、C（498.9~684.9 cm³）3组,每组10例,平均体积分别为151.5、327.1和583.3 cm³。使用呼吸运动模拟平台带动含二维电离室矩阵的模体沿枪靶方向运动。分别转动准直器至0°和90°,在不同呼吸运动幅度（0、4、8、12和15 mm）与周期（3、4和5 s）下,采集模体等中心层面剂量。其中周期为4 s测量5次,以绝对剂量及γ通过率（3 mm/3%）为指标,分析采集剂量与治疗计划系统（TPS）输出的剂量分布差异。结果 在两个方向上,呼吸运动降低了靶区边缘内侧剂量,提高了靶区边缘外侧剂量。呼吸运动周期之间的γ通过率差异最大达3.54%（t=2.301,P<0.05）。当呼吸运动幅度超过8 mm时,γ通过率<90%,且随幅度增大而减小。静态与呼吸运动之间γ通过率的差值和靶区体积呈负相关,A、B、C 3组的平均γ通过率依次增大。5次叠加剂量的γ通过率高于单次剂量平均γ通过率,且差异有统计学意义（t=-9.36~-5.95,P<0.05）。结论 动态IMRT靶区剂量分布主要受呼吸运动幅度及自身体积影响,部分幅度下呼吸运动周期对剂量分布有影响。多次剂量实施后,可消除部分单次剂量实施误差。医师需要根据呼吸运动幅度对靶区进行合理外扩,同时优化呼吸运动方向上靶区边缘组织受量。对于靶区体积过小以及呼吸运动幅度过大的患者,应采取呼吸管理技术提高靶区剂量实施的精准性。     

基于四分位距值的调强放疗计划剂量体积直方图分析

目的 提出一种基于四分位距值的调强放射治疗（IMRT）计划靶区及危及器官剂量体积直方图（DVH）差异分析方法。方法 回顾分析22例宫颈癌IMRT计划,将靶区和危及器官（膀胱、直肠和左右股骨头）5组DVH曲线从Pinnacle³计划系统中导出,对每组DVH曲线求出平均DVH曲线和四分位距值曲线。结果 计划靶区DVH在54.03 Gy处差异最大,四分位距值为6.95%,处方剂量包绕的靶区体积为（96.43±1.63）%。膀胱DVH在17.24 Gy处差异最大,四分位距值为14.62%,V₄₀和V₃₀分别为（32.79±7.06）% 和（56.47±9.94）%。直肠DVH在35.92 Gy处差异最大,四分位距值为19.94%,V₄₀和V₃₀分别为（30.17±10.80）%和（58.16±11.99）%。膀胱与直肠的四分位距值差异有统计学意义（z=-6.59, P<0.05）。左侧股骨头DVH在16.06 Gy处差异最大,四分位距值为31.47%。右侧股骨头DVH在17.47 Gy处差异最大,四分位距值为32.82%,左右股骨头间的四分位距值间差异无统计学意义（P>0.05）。结论 四分位距值曲线可以分析靶区和危及器官DVH曲线的变化趋势,为自动计划优化参数设置提供指导。     

Differentiation of Adrenal Adenoma and Nonadenoma in Unenhanced CT: New Optimal Threshold Value and the Usefulness of Size Criteria for Differentiation

Objective

To determine the optimal threshold for the attenuation values in unenhanced computed tomography (CT) and assess the value of the size criteria for differentiating between an adrenal adenoma and a nonadenoma.

Materials and Methods

The unenhanced CT images of 45 patients at our institution, who underwent a surgical resection of an adrenal masses between January 2001 and July 2005, were retrospectively reviewed. Forty-five adrenal masses included 25 cortical adenomas, 12 pheochromocytomas, three lymphomas, and five metastases confirmed by pathology were examined. The CT images were obtained at a slice thickness of 2 mm to 3 mm. The mAs were varied from 100 to 160 and 200 to 280, while the 120 KVp was maintained in all cases. The mean attenuation values of an adrenal adenoma and nonadenoma were compared using an unpaired t test. The sensitivity, specificity, positive predictive value, negative predictive value, and accuracy at thresholds of 10 HU, 20 HU, and 25 HU were compared. The diagnostic accuracy according to the size criteria from 2 cm to 6 cm was also compared.

Results

The twenty-five adenomas showed significantly lower (p < 0.05) attenuation values(mean ± SD; 16.3 ± 14.9) than the nonadenomas (38.1 ± 6.8). Nineteen (90%) of the 20 nonadenomas had attenuation values ranging from 30 to 50 HU. The sensitivity, specificity, positive predictive value, negative predictive value, and accuracy for diagnosing adenomas were 36%, 100%, 100%, 56%, and 64%, respectively, at a threshold of 10 HU; 60%, 100%, 100%, 67%, and 78%, respectively, at a threshold of 20 HU; and 72%, 95%, 95%, 73%, and 82%, respectively, at a threshold of 25 HU. The adenomas had a significantly (p < 0.05) smaller diameter (2.44 ± 1.24 cm) than the nonadenomas (5.09 ± 2.37 cm). The size criteria using a diameter of 4-6 cm showed a sensitivity > 90% but a specificity < 70%. Size criteria of 2 or 3 cm had a high specificity of 100% and 80% but a low sensitivity of 20% and 60%.

Conclusion

The threshold attenuation values of 20 or 25 HU in the unenhanced CT appear optimal for discriminating an adrenal adenoma from a nonadenoma. The size criteria are of little value in differentiating adrenal masses because of their low specificity or low sensitivity.     

A study on correlation between 2D and 3D gamma evaluation metrics in patient-specific quality assurance for VMAT

In this study, we investigated the correlation between 2-dimensional (2D) and 3D gamma analysis using the new PTW OCTAVIUS 4D system for various parameters. For this study, we selected 150 clinically approved volumetric-modulated arc therapy (VMAT) plans of head and neck (50), thoracic (esophagus) (50), and pelvic (cervix) (50) sites. Individual verification plans were created and delivered to the OCTAVIUS 4D phantom. Measured and calculated dose distributions were compared using the 2D and 3D gamma analysis by global (maximum), local and selected (isocenter) dose methods. The average gamma passing rate for 2D global gamma analysis in coronal and sagittal plane was 94.81% ± 2.12% and 95.19% ± 1.76%, respectively, for commonly used 3-mm/3% criteria with 10% low-dose threshold. Correspondingly, for the same criteria, the average gamma passing rate for 3D planar global gamma analysis was 95.90% ± 1.57% and 95.61% ± 1.65%. The volumetric 3D gamma passing rate for 3-mm/3% (10% low-dose threshold) global gamma was 96.49% ± 1.49%. Applying stringent gamma criteria resulted in higher differences between 2D planar and 3D planar gamma analysis across all the global, local, and selected dose gamma evaluation methods. The average gamma passing rate for volumetric 3D gamma analysis was 1.49%, 1.36%, and 2.16% higher when compared with 2D planar analyses (coronal and sagittal combined average) for 3 mm/3% global, local, and selected dose gamma analysis, respectively. On the basis of the wide range of analysis and correlation study, we conclude that there is no assured correlation or notable pattern that could provide relation between planar 2D and volumetric 3D gamma analysis. Owing to higher passing rates, higher action limits can be set while performing 3D quality assurance. Site-wise action limits may be considered for patient-specific QA in VMAT.     

基于放射组学的机器学习预测盆腔调强放疗剂量验证的γ通过率

目的利用放射组学特征构建不同的机器学习分类模型, 预测盆腔肿瘤调强放疗剂量验证的γ通过率, 并探讨最佳预测模型。方法回顾性分析196例盆腔肿瘤调强放疗计划, 采用基于模体测量方式的三维剂量验证结果, γ通过率标准为3%/2 mm、10%剂量阈值。提取基于剂量文件的放射组学特征构建预测模型。分别采用随机森林、支持向量机、自适应增强和梯度提升决策树4种机器学习算法, 计算曲线下面积(AUC)值、敏感度和特异度, 评估4种预测模型的分类性能。结果随机森林、支持向量机、自适应增强、梯度提升决策树模型的灵敏度和特异度分别为0.93、0.85, 0.93、0.96, 0.38、0.69, 0.46、0.46。随机森林模型和自适应增强模型的AUC值分别为0.81和0.82, 支持向量机和梯度提升决策树模型的AUC值为0.87。结论针对盆腔肿瘤调强放疗计划, 可以采用基于放射组学特征的机器学习方法来构建γ通过率的预测模型。支持向量机模型和梯度提升决策树模型的分类性能要优于随机森林模型、自适应增强模型。     

Initial experience of ArcCHECK and 3DVH software for RapidArc treatment plan verification

The purpose of this study was to perform delivery quality assurance with ArcCHECK and 3DVH system (Sun Nuclear, FL) and to evaluate the suitability of this system for volumetric-modulated arc therapy (VMAT) (RapidArc [RA]) verification. This software calculates the delivered dose distributions in patients by perturbing the calculated dose using errors detected in fluence or planar dose measurements. The device is tested to correlate the gamma passing rate (%GP) and the composite dose predicted by 3DVH software. A total of 28 patients with prostate cancer who were treated with RA were analyzed. RA treatments were delivered to a diode array phantom (ArcCHECK), which was used to create a planned dose perturbation (PDP) file. The 3DVH analysis used the dose differences derived from comparing the measured dose with the treatment planning system (TPS)-calculated doses to perturb the initial TPS-calculated dose. The 3DVH then overlays the resultant dose on the patient׳s structures using the resultant “PDP” beams. Measured dose distributions were compared with the calculated ones using the gamma index (GI) method by applying the global (Van Dyk) normalization and acceptance criteria, i.e., 3%/3 mm. Paired differences tests were used to estimate statistical significance of the differences between the composite dose calculated using 3DVH and %GP. Also, statistical correlation by means of logistic regression analysis has been analyzed. Dose-volume histogram (DVH) analysis for patient plans revealed small differences between treatment plan calculations and 3DVH results for organ at risk (OAR), whereas planning target volume (PTV) of the measured plan was systematically higher than that predicted by the TPS. The t-test results between the planned and the estimated DVH values showed that mean values were incomparable (p < 0.05). The quality assurance (QA) gamma analysis 3%/3 mm showed that in all cases there were only weak-to-moderate correlations (Pearson r: 0.12 to 0.74). Moreover, clinically relevant differences increased with increasing QA passing rate, indicating that some of the largest dose differences occurred in the cases of high QA passing rates, which may be called “false negatives.” The clinical importance of any disagreement between the measured and the calculated dose is often difficult to interpret; however, beam errors (either in delivery or in TPS calculation) can affect the effectiveness of the patient dose. Further research is needed to determinate the role of a PDP-type algorithm to accurately estimate patient dose effect.     

Description and evaluation of a new volumetric-modulated arc therapy plan complexity metric

This study describes a new plan complexity metric for volumetric-modulated arc therapy (VMAT) and evaluates the relationship of this metric with the VMAT dosimetric accuracy. The new modulation complexity score for VMAT (NMCSv) that is based on the aperture shape and multi-leaf collimator (MLC) leaf travel is described. Its performance is evaluated through correlation and receiver operating characteristic (ROC) analyses with patient-specific gamma passing rates using 2 3-dimensional diode arrays. For comparison, the following metrics are evaluated using the same correlation analyses: average field width, average leaf travel, modulation complexity score, and leaf travel modulation complexity score. Spearman's rank correlation analysis is performed to examine any relationships between the complexity metrics and the patient-specific gamma passing rates. ROC curves are used to assess the performance of the plan metrics using a gamma passing rate of 3%/3 mm criterion with a 95% tolerance level. In both the diode arrays, the gamma passing rates (3%/3 mm and 2%/2 mm) for patient-specific dosimetric verification of VMAT plans are moderately or weakly correlated to all the complexity metrics. NMCSv demonstrates the highest correlation with the passing rates (r = 0.652, p < 0.001 for Delta4 and r = 0.499, p < 0.001 for ArcCheck) and the highest area under the curve value (0.809, p < 0.01 for Delta4 and 0.734, p < 0.01 for ArcCheck). While using the Delta4 system, NMCSv exhibits an excellent classification performance with area under the curves of 0.926 (sensitivity: 0.913; specificity: 0.860; p < 0.01) and 0.918 (sensitivity: 0.943; specificity: 0.720; p < 0.01) for rectal and cervical cancer plans, respectively. NMCSv as a novel potential clinical plan complexity metric is moderately correlated with the gamma passing rate. It demonstrates the best performance with respect to distinguishing the dosimetric accuracy of VMAT plans among the evaluated metrics. The classification performance of complexity metrics can be affected by various dosimetry verification devices and treatment sites.     

Dose verification of virtual bolus application for helical tomotherapy

The objective of the study is to verify the dose delivered on helical tomotherapy based on treatment plan with varying virtual bolus (VB) thickness. The target was localized on the ArcCHECK image by 3 mm margin from the phantom surface. The dimension of target, which includes the ArcCHECK's detectors, with the 4.0 cm width and length 12.0 cm along the phantom The 5 treatment plans were generated, 1 plan without VB application (NoVB) and the 4 plans with varying of VB thickness on the phantom surface by 0.5 cm (VB0.5), 1.0 cm (VB1.0), 1.5 cm (VB1.5), and 2.0 cm (VB2.0), in treatment planning but absent during irradiation. For measurement analysis, the ionization chamber and the ArcCHECK detectors were used for point dose and dose distribution by investigating the percentage of dose difference and the gamma passing rate. The VB thickness 0.5, 1.0 and 1.5 cm showed acceptable value with less than 2% for dose difference by 0.37% (VB0.5), -0.11% (VB1.0) and -0.37% (VB1.5) at the center of ArcCHECK. The accuracy of dose distribution showed an acceptable gamma passing rate of 99.8% (VB0.5), 100% (VB1.0), and 90.2% (VB1.5) for gamma criteria by 3%/3mm for absolute dose analysis. However, the gamma passing rate of VB2.0 down to 71.2% of absolute mode for gamma criteria by 3%/3mm. The treatment plans with VB thickness less than 15 mm deliver doses that are comparable to treatment plans without virtual bolus based on gamma analysis. However, the deviation showed a trend increasing when VB thickness increased. The VB2.0 was not acceptable for point dose and dose distribution verification by more than 2% dose difference and less than 90% of gamma passing rate.     

Three-dimensional gamma analysis of dose distributions in individual structures for IMRT dose verification

Our purpose in this study was to implement three-dimensional (3D) gamma analysis for structures of interest such as the planning target volume (PTV) or clinical target volume (CTV), and organs at risk (OARs) for intensity-modulated radiation therapy (IMRT) dose verification. IMRT dose distributions for prostate and head and neck (HN) cancer patients were calculated with an analytical anisotropic algorithm in an Eclipse (Varian Medical Systems) treatment planning system (TPS) and by Monte Carlo (MC) simulation. The MC dose distributions were calculated with EGSnrc/BEAMnrc and DOSXYZnrc user codes under conditions identical to those for the TPS. The prescribed doses were 76 Gy/38 fractions with five-field IMRT for the prostate and 33 Gy/17 fractions with seven-field IMRT for the HN. TPS dose distributions were verified by the gamma passing rates for the whole calculated volume, PTV or CTV, and OARs by use of 3D gamma analysis with reference to MC dose distributions. The acceptance criteria for the 3D gamma analysis were 3/3 and 2 %/2 mm for a dose difference and a distance to agreement. The gamma passing rates in PTV and OARs for the prostate IMRT plan were close to 100 %. For the HN IMRT plan, the passing rates of 2 %/2 mm in CTV and OARs were substantially lower because inhomogeneous tissues such as bone and air in the HN are included in the calculation area. 3D gamma analysis for individual structures is useful for IMRT dose verification.     

Dosimetric impact of translational and rotational setup errors for spine stereotactic body radiotherapy: A phantom study

This study aimed to investigate experimentally the effect of translational and rotational setup errors on 3-dimensional dose distributions by using the gamma index and dose volumetric indices for spine stereotactic body radiotherapy. Treatment plans were designed in accordance with the Radiation Therapy Oncology Group (RTOG) 0631 protocol. Measurements were taken using a Delta4 phantom (ScandiDos, Uppsala, Sweden). Setup errors were generated using the HexaMotion 6D moving platform (ScandiDos). Dose distributions in the presence of setup errors were evaluated, according to the γ passing rate with the 3% and 2?mm criteria (γ_3%/2?mm) and dose volumetric indices (D₉₀ for the target volume and D₂ for the spinal cord), using the Delta4 device (ScandiDos). The sensitivity coefficient, which represented the correlation between the γ_3%/2?mm passing rate and dose volumetric indices, was determined to assess robustness against setup errors. Rotational setup errors of 2° were equivalent to translational setup errors of 2?mm for the γ_3%/2?mm passing rate, D₉₀ for the target, and D₂ for the spinal cord. D₉₀ for the target had low robustness against a translational setup error in the vertical direction and a rotational setup error in the pitch direction. D₂ for the spinal cord was sensitive to a translational setup error in the lateral direction and a rotational setup error in the roll direction. The positioning accuracy of the rotational setup error, corresponding to the tolerance level of image-guided radiotherapy in the RTOG 0631 protocol, was required to be?≤?2°.     

Derivation of in vivo source tracking error thresholds for TRUS-based HDR prostate brachytherapy through simulation of source positioning errors

PurposeThe purpose of this study was to simulate treatment planning source positioning errors in transrectal ultrasound–based real-time high-dose-rate prostate brachytherapy treatments and determine appropriate in vivo source tracking error thresholds.Methods and MaterialsTreatment planning source positioning errors were simulated for 20 patient plans in the brachytherapy treatment planning system by manually adjusting the dwell position coordinates within selected catheters without plan reoptimization. The change in dose-volume histogram (DVH) indices was calculated as a function of the source positioning error. The magnitude of the change in the DVH indices was then used to derive appropriate in vivo source tracking error thresholds.ResultsSource positioning error thresholds to prevent potentially significant changes in prostate (target) DVH metrics ranged from 2 to 5 mm, dependent on the direction of the source positioning error, as well as the relative weight of the dwell position within the plan, and its position relative to the patient anatomy. Source positioning error thresholds to prevent potentially clinically significant changes in organ at risk DVH metrics were found to be complex and patient-dependent.ConclusionsIn vivo source tracking error thresholds for transrectal ultrasound–based real-time high-dose-rate prostate brachytherapy were investigated via the simulation of treatment planning source positioning errors. These error thresholds were found to be dependent not only on the direction of the error, but also on the endpoint. There is still the potential for larger changes in DVH indices to occur for catheter shifts smaller than the proposed threshold levels in this study.