楔形滤过板在大射野应用中的剂量特性

在放疗中对乳腺切野、腰、骶骨及盆腔侧向部位照射时 ,采用大射野楔形滤过板照射技术。为使放疗医生掌握大楔形野的临床剂量特性 ,保证疗效[1 ] ,本文作者提出了楔角随深度、射野变化的影响及楔形因子和加入楔板使束流硬度提高的问题。一、材料和方法使用Ｔｈｒｏｄｏｓｅ三维自动测量水箱 ,用半导体探头对 3种楔形板 (1 5°、30°、45°)射野从 5ｃｍ× 5ｃｍ～ 2 0ｃｍ× 2 0ｃｍ ,用Ｃｌｉｎａｃ 1 80 0 6ＭＶＸ射线测量ＰＤＤ曲线及一系列不同深度的截面剂量分布 ,绘出 1 0 0 %、90 %、80 %、70 %、60 %和 50 %的等剂量曲线确定楔角。用…     

非对称野校正系数的测量

独立准直器已成为直线加速器的标准配置，准直器的四个叶片分别由四个电机驱动，可形成射野中心偏离线束中心轴的射野，此类射野称非对称或偏轴射野，非对称野在用干共面或非共面相邻野的衔接时，可避免在相邻区出现剂量不均匀的现象，在放疗过程中需要缩野，扩野或复发再程治疗时，可使用非对称野，而保持等中心位置不变。随着临床应用越来越多，对非对称野校正系数的测量就显得很重要。     

SIEMENS PRIUMS M 5176直线加速器物理楔形及动态楔形分析

目的:研究SIEMENS PRIUMS M 5176直线加速器中物理楔形因子和动态楔形因子影响因素,并得出结论,为临床准确使用该因子提供依据。方法:在固体水膜体中利用指形电离室对6 MV和10 MV射线束下不同角度物理楔形板和动态楔形板分别测量加和不加楔形滤片时的剂量率来计算楔形因子。通过测量不同角度的物理楔形板和动态楔形板在固定照射野(10 cm×10 cm)的不同深度下的楔形因子来研究楔形因子随深度的变化规律。同时,对于楔形因子随射野的变化规律,还测量了不同角度的物理楔形板和动态楔形板在固定深度(d=10 cm)下的不同射野大小的楔形因子。结果:深度对于物理楔形板的楔形因子较为明显,深度增加时楔形因子增大,且随着楔形角的增大变化更明显。对于物理楔形板,当深度由最大深度1.5 cm增加到10 cm时,对于6 MV物理楔形板,它们楔形因子最大为60°增加约3.29%;对于10 MV物理楔形板,楔形因子最大为60°增加了约1.50%。对于6 MV动态楔形板,楔形因子最大为60°增加了1.01%、对于10 MV动态物理楔形板,楔形因子增加了约0.9%;物理楔形因子与射野大小有一定关系。它随着射野增大而增大,楔形因子最大为60°增加了约7.8%对于6 MV能量;楔形因子最大为60°增加了约8.0%对于10 MV能量。与物理楔形因子不同看到动态楔形因子受射野大小影响很小。它随着射野增大和楔形度数的增大而增大但是不明显的,它们楔形因子最大为60°分别为对1.0%对于6 MV和0.8%对于10 MV能量。结论:深度和射野对于物理楔形因子及动态楔形因子都有影响。但动态楔形因子的影响较小,且动态楔形板在治疗中要比物理楔形板优越。尽管动态楔形板在调试过程中有一定的困难。主要是因为在临床剂量计算时使用动态楔形板时对比剂量的影响相对于物理楔形板来说要小很多,因此笔者建议有条件的医院因尽量使用动态楔形板来作为剂量分布的调整。     

直线加速器非对称准直系统对楔形因子和楔形角的影响

直线加速器非对称准直系统对楔形因子和楔形角的影响韩树奎，路长春当前，许多现代新型医用电子直线加速器对其产生的Ｘ射线配有非对称准直系统，由此形成的射野称为＂偏轴射野＂。挡束流中心轴的偏轴射野，由于其具有半影区小的特点，在放射治疗中可很好地保护靠近肿瘤的...     

一种计算不规则野的散射剂量的方法研究

目的寻找一种可用于计算放射治疗不规则野的散射剂量的可靠方法。方法通过对原用于计算规则野等效方野的Day氏函数法进行改进,使之扩大应用到不规则野,从而既能计算不规则野的等效方野,也可以计算不规则野中任意点的散射剂量。结果改进后的Day氏函数随照射深度的变化进行修正,大大提高了计算精度,不规则野的散射剂量的计算误差在1.5%以内。结论用改进的Day氏函数法可以计算不同照射能量和照射深度的任意形状射野的散射剂量,并取得满意的精度。     

一种确定立体定向放疗VMAT计划处方等剂量线的方法

目的 建立一种确定立体定向放疗（SRT）容积调强弧形治疗（VMAT）计划处方等剂量线（IDL）的方法。方法 选取8例SRT脑转移瘤患者,靶区体积范围3.5~11.7 cm³（中位数6.1 cm³）。采用VMAT技术,首先对每一个靶区设计相同处方剂量的参考计划。然后,采用原靶区内收一定几何边界生成的新靶区来进行优化计算,从而得到不同IDL的计划。研究不同靶区达到最优IDL范围所需内收的最小几何边界。结果 所有靶区达到最优IDL范围所需内收的最小边界均为4或5 mm,其得到的平均IDL为（66.05±0.02）%。最优IDL计划同参考计划相比,平均梯度指数（GI）从4.05±0.39下降到3.37±0.24,下降了20%（Z=-2.521,P<0.05）。正常脑组织中V₄₀、V₃₀、V₅以及平均剂量分别下降了11.5%（Z=-1.973,P<0.05）、7.2%（Z=-2.105,P<0.05）、12.8%（Z=-2.521,P<0.05）以及8.1%（Z=-2.382,P<0.05）,V₂₀、V₁₀以及适形度指数无明显差异（P>0.05）。结论 采用靶区内收生成新的靶区进行计划设计的方法可以用于SRT-VMAT计划IDL的优化。靶区内收4或5 mm进行计划设计可以使IDL达到最优范围,从而可以降低GI值以及更好地保护正常脑组织。     

6 MV光子束均整与非均整模式蒙特卡罗模型的绝对剂量刻度与输出因子模拟

目的探讨TrueBeam加速器6 MV光子束均整（FF）与非均整（FFF）模式蒙特卡罗模型的绝对剂量刻度与射野输出因子计算方法。方法利用BEAMnrc程序分别建立FF与FFF两种模式在靶到监测电离室（BEAM_up）和监测电离室以下组件部分（BEAM_down）的加速器机头模型,计算入射电子和经次级准直器反射后的粒子在监测电离室的剂量沉积,利用DOSXYZnrc程序计算入射电子在射野中心轴上特定深度处的剂量沉积,结合绝对剂量刻度公式计算标准射野刻度因子和射野输出因子（1 cm×1 cm~40 cm×40 cm）。结果 FF与FFF模型的10 cm×10 cm标准辐射野,1 MU相当于7.747×10¹³±3.099×10¹¹和3.248×10¹³±1.624×10¹¹电子打靶,在虚拟的加速器监测电离室上产生21.53和35.01 cGy剂量;FF与FFF模式射野输出因子模拟值与测量值偏差为0.72%±1.4%和0.56%±0.78%。结论该模型输出因子模拟与测量结果符合度较好,绝对剂量计算精度较高,可以用于临床剂量学研究。     

筒串卷积算法用于非均匀介质光子剂量计算的精确性验证

目的 验证筒串卷积算法(CCC)预测射野剂量分布的精确性.方法 采用MatriXX系统测量均匀模体中的剂量分布,然后利用热释光探测器(TLD)对两种不同的非均匀模体结构中的剂量分布进行实验验证.将Philips Pinnacle3 Version 8.0商业TPS中CCC算法和FC算法的计算值与实验测量值进行比较.所有实验均在Varian 23EX直线加速器上进行,射野大小分别为5cm×5cm和10cm×10cm,采用6MV光子束,源皮距(SSD)=100cm.结果 在均匀介质中,两种算法都能精确地预测射束的剂量分布,在非均匀介质中,组织密度的不均匀和射野大小对剂量分布有着很重要的影响,CCC算法的计算值与测量值之间的误差小于FC算法.结论 CCC算法能够更精确地预测射束剂量分布.     

用能量沉积核函数方法计算~(60)Co照射野的吸收剂量

目的　介绍了用能量沉积核函数方法计算60 Co照射野吸收剂量的方法。方法　能量沉积核函数方法将吸收剂量的贡献分为 3部分 :原射线、单次散射和多次散射。它使用基本的剂量学数据 ,如射野中心轴百分深度剂量、离轴比和准直系统散射输出因子等 ,这些数据在Fyc 5 0H治疗机上用方形照射野测量得到。再用能量沉积核函数计算吸收剂量。并讨论了散射线对吸收剂量的影响。结果　从测量数据得到了原射线和散射线的能量沉积核函数 ,并利用能量沉积核函数计算60 Co照射野的主要剂量学参数 ,计算值和测量值是一致的 ;不规则照射野的吸收剂量及其分布的计算结果也和测量结果符合得很好。结论　能量沉积核函数方法适用于较精确地计算60 Co不规则照射野的吸收剂量。     

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。     

Implementation of enhanced dynamic wedges in pinnacle treatment planning system

Enhanced dynamic wedges (EDW) provide many advantages over traditional hard wedges for linear accelerator treatments. Along with these advantages comes the responsibility of ensuring that this complex technology delivers the correct dose to patients. This involves determining the enhanced dynamic wedge factors for various field sizes and depths for use in the hand calculation of monitor units (MUs). The accurate representation of dynamic wedges in the treatment planning computer must also be ensured. This is required so that the final isodose distributions are correct and the MUs calculated by the treatment planning computer match those determined by hand calculation. We have commissioned and implemented the use of EDW in the Pinnacle radiation therapy planning system. The modeled dose profiles agree with the measured ones with a maximum difference of 2%. The MUs generated by Pinnacle are also within 2% of those calculated independently. The process of data collection and verification, beam modeling, and a discussion of a potential pitfall encountered in this process are presented in this paper.     

Implementation of enhanced dynamic wedges in pinnacle treatment planning system

Enhanced dynamic wedges (EDW) provide many advantages over traditional hard wedges for linear accelerator treatments. Along with these advantages comes the responsibility of ensuring that this complex technology delivers the correct dose to patients. This involves determining the enhanced dynamic wedge factors for various field sizes and depths for use in the hand calculation of monitor units (MUs). The accurate representation of dynamic wedges in the treatment planning computer must also be ensured. This is required so that the final isodose distributions are correct and the MUs calculated by the treatment planning computer match those determined by hand calculation. We have commissioned and implemented the use of EDW in the Pinnacle radiation therapy planning system. The modeled dose profiles agree with the measured ones with a maximum difference of 2%. The MUs generated by Pinnacle are also within 2% of those calculated independently. The process of data collection and verification, beam modeling, and a discussion of a potential pitfall encountered in this process are presented in this paper.     

Examination of formula for enhanced dynamic wedge factors in symmetric and asymmetric fields

We proposed a formula for the enhanced dynamic wedge (EDW) factor in the half-field (HF) that combined the formula proposed by Liu et al. in 1998 and their formula in 2003. When the EDW was used for irradiation to the tangent line of the HF breast, the values calculated by our formula and the measured values were consistent within 0.5%. We showed that our proposed formula was useful, easy to use, and more accurate than the conventional formula. The purpose of this study was to examine the available range of the wedge factor of symmetrical and asymmetric EDW calculated by our formula. As a result of the examination, the values calculated by our formula and the measured values were consistent within 2% except for highly asymmetric EDW. We created a spreadsheet to calculate the wedge factor easily and accurately. We will examine the reason why the calculated and measured values were greater than 2%, and improve our formula so that it can be used in a wider range.     

Verification of a simple point dose calculation method for a dual energy linear accelerator with asymmetric jaws

Certain fundamental dosimetrical parameters involving the applications of asymmetric jaws were investigated. The nominal accelerating potentials (NAPs) were found to decrease from 5.1 to 4.2 and from 18.0 to 13.4 for the 6 and 18 MV beams, respectively, as the off-axis distance (OAD) increases from 0.0 to 15.0 cm. The relative beam intensity increases from 1.00 to 1.07 at OAD of 15.0 cm for the 6 MV beam, and to 1.02 at OAD of 7.0 cm for the 18 MV beam. The percentage depth doses (PDDs) for half-blocked fields of 4 × 4 cm, 10 × 10 cm and 20 × 20 cm were found to deviate from those of corresponding symmetric fields by less than 2% down to the depth of 35.0 cm. The field size factor (FSF) for the asymmetric field from 4 × 4 cm to 20 × 20 cm deviates less than 1.0% from those of the corresponding symmetric fields. The equivalent square concept was found to be applicable to asymmetric fields within 1% error if the jaw exchange effect is taken into consideration. The measured point doses for half-blocked fields of 4 × 4 cm, 10 × 10 cm and 20 × 20 cm for both 6 and 18 MV were within 3% of the calculated dose based on a published dose calculation method which employs symmetric field beam parameters, such as field size factor (FSF), percentage depth dose (PDD), and off-axis correction factors (OAFs). The efficacy of this point dose calculation method is discussed.     

Verification of dose calculations with a treatment planning system for open and wedged fields of a Co unit with a new asymmetric collimator

A Cobalt-60 treatment unit was equipped with a new collimator with asymmetrical capability of both the X-and Y-jaws. This new collimator design opens possibilities for treatment techniques with this apparatus, which, until now, were only achievable with linear accelerators. Before accepting the device and taking it into clinical routine, a dosimetric verification was performed, which compared results of dose measurements with the results of dose calculations of the treatment planning system. For this purpose, the approach of Report 55 of the AAPM Task Group 23 for testing a treatment planning system was followed, with modifications to comply with the asymmetrical settings of the fields. The study shows that criteria for acceptance of the treatment planning algorithm were met for the asymmetrical open fields and for asymmetrical fields with a 22° and a 45° wedge. However, deviations tended to be too high under the thick part of the thickest wedge.