应用电离室矩阵进行挡铅射野的验证的方法探讨

目的:探讨利用二维电离室矩阵MatriXX进行挡铅射野质量保证的方法及可靠性。方法:将治疗计划系统(TPS)中的铅块信息以dat的文件格式传递给Hek Medical System热丝切割机,根据dat文件做出相应的铅挡块,将铅挡块放至直线加速器的托架上,出束照射,用二维电离室矩阵MatriXX进行测量,从而获得挡铅射野的形状。应用matlab软件编程对由TPS导出的dat文件进行处理,绘制出射野在等中心平面处的形状和大小。将MatriXX电离室矩阵测得的射野的50%等剂量线和matlab绘制出的射野形状由photoshop软件进行比较分析。结果:笔者通过对20个TPS实测射野和计划射野的比较分析,发现二者总体上能够相符,只是在射野边缘尤其是连续变化的曲线边缘的细节表现上略微有些差异,它们综合位置差为0.631 mm,均方差为0.776 mm。结论:TPS实测射野和计划射野的吻合度非常高,基本满足放射治疗中对挡铅射野误差在5 mm以内的要求。     

二维电离室矩阵中射野边界位置对调强验证Gamma通过率的影响

目的:针对(10×10)cm~2射野,探讨改变射野边界在矩阵中的位置对测量射野大小及Gamma(γ)通过率的影响。方法:使用MatriXX二维电离室矩阵测量(10×10)cm~2射野剂量分布,保持射野大小不变,移动X方向准直器和在Y方向移动治疗床两种方式改变射野边界在矩阵中的位置,用OmniPro I'mRT(1.7)软件分析每次移动0.1 cm时射野边长的改变量,同时用实测剂量分布和XiO(4.40)治疗计划系统相应射野剂量分布对比,记录3%/3 mm评估标准下的γ通过率和γ为100%时的评估标准。结果:在矩阵电离室腔外间隙射野边长改变量低于0.1 cm,且在每两个电离室腔外间隙正中改变量最小接近0.05 cm;在电离室腔体内改变量高于0.1 cm,且在每一个电离室腔体中心接近最大值0.2 cm。3%/3 mm下的γ结果显示射野边界不通过点数随位置变化明显不同,在射野边长改变量最大和最小附近通过率高,全部通过的评估标准范围是2%/2 mm至6%/3 mm。结论:选取射野边界在矩阵电离室腔体中心或腔外间隙正中位置时,所测射野大小偏差最小。同时上述射野边界位置γ通过率最高,因此,在调强计划剂量分布验证中要充分考虑射野剂量梯度较大处在电离室矩阵的位置对γ通过率的影响,可调整剂量分布在矩阵中位置或改变不同评估标准详细分析γ通过率差异,从而提高γ通过率的有效性,对临床工作具有一定的指导作用。     

三维分析仪与两维矩阵射野测量的比较

目的:应用不同仪器与方法测量加速器6 MV X线射野的特性,比较各方法的优劣和局限性,探讨快速简便检测射野特性的方法。材料与方法:分别采用电离室和半导体探头配合三维射野分析仪测量加速器6 MV X线不同射野大小的百分深度剂量曲线PDD和离轴比曲线OCR,并以二维电离室矩阵测量相同条件的OCR。(1)比较采用电离室和半导体探头测量PDD的差别。(2)比较两维矩阵与电离室半导体探头测量射野的对称性、平坦度、射野大小和半影等的差别。结果:对小于15 cm×15 cm照射野,半导体探头和电离室测量PDD的结果一致性较好,两者偏差小于1.3%。对于20 cm×20 cm照射野,半导体探头的测量结果大于电离室,最大差别3.5%,偏差为2.6%。用半导体探头与电离室测量射野的大小,两者的最大差别为0.6 mm,两者有较好的一致性,二维电离室矩阵测量与前两者比较,最大差别为2.9 mm,最小差别0.5 mm。三种方法测量的射野平坦度差别在1.2%~2.6%,矩阵的测量数值在半导体和电离室测量范围之内。结论:在检测加速器射野性能时,二维矩阵可以快速检测射野平坦度、对称性,但测量射野大小时可能有较大误差,不宜用作验收加速器和收集...     

应用MatriXX测量西门子PRIMUS加速器治疗床的金属部件对射野剂量分布的影响

目的:测量西门子PRIMUS加速器治疗床的金属部件对射野剂量分布的影响。方法:PRIMUS加速器治疗床由可拆卸的床头、网状碳纤维床板和有机玻璃床板三部分组成,3种床板均有金属部件。本文将MatriXX夹在上下各6 cm厚的IBA固体水体模的中间,对齐MatriXX的测量中心轴与治疗床的中心纵轴,SAD为100 cm,首先通过旋转机架分别确定10 cm×10 cm射野能照到3种床板的金属部件的机架角度范围分别是110°~135°(对侧225°~250°)、115°~140°(对侧220°~245°)、155°~180°(对侧180°~205°)。然后采用6 MV X射线,在上述角度区间每间隔5°设一个野,机器跳数为50 MU,分别进行测量。接着在有机玻璃床板上悬空MatriXX,其它条件不变,重复测量不受治疗床影响下的剂量分布。最后对比分析金属部件的衰减影响。结果:3种床板的金属部件对射线的衰减,在等中心处分别为2.1%~22.4%、1.3%~43.8%、0%~46.7%,最大剂量衰减值分别为12.1%~32.2%、12.9%~65.3%、32.8%~58.3%。结论:PRIMUS加速器治疗床的金属部件对射野剂量分布有较大影响,在治疗摆位时须避开。     

治疗床两侧金属C型臂对吸收剂量的影响

目的:研究加速器治疗床两侧金属C型臂对吸收剂量的影响。方法:测量模体置于治疗床板中央,电离室插孔到床板距离分别为5 cm和10 cm。右侧C型臂分别置于7个不同角度,确定不同面积射野经过C型臂时的机架角度。利用0.6 cc电离室测量6 MV和15 MV X线经过C型臂后固定野照射吸收剂量的变化,以及C型臂位置对旋转照射吸收剂量的影响。结果:机架角为90°～180°,治疗床右侧C型臂位于R7位置时,机架角度布野受限范围最大;机架角布野受限范围随射野面积的增大而增大,随治疗深度的减小而增大。对固定野照射,射线能量越小,吸收剂量的衰减越大;射线穿过C型臂的距离越大,吸收剂量的衰减越大;旋转照射时C型臂位置越靠近床板中心轴,吸收剂量衰减越大。结论:治疗床两侧金属C型臂对射线有衰减和散射,造成吸收剂量及其分布发生变化。治疗计划设计和患者摆位时应尽量避开金属C型臂。     

均整与非均整模式下TrueBeam加速器治疗床对放疗剂量的影响

目的:探讨均整(FF)与非均整(FFF)模式下瓦里安TrueBeam加速器全碳纤维治疗床对模体中心和表面剂量的影响。方法:将30 cm×30 cm×20 cm的固体水模分别放置于治疗床薄、中、厚段上,模体的中心与加速器等中心重合,德国IBA FC65-G电离室测量等中心的剂量;选取6/10 MV光子束FF/FFF模式4档能量,10 cm×10 cm标准射野,等中心照射,以机架转角0°～80°(间隔10°采样)为参考,计算100°～180°范围与对应角度参考剂量的比值得到对应角度的穿透因子;将EBT3胶片分别置于上述模体表面和底部,对应机架角度为0°和180°,分析相应的百分深度剂量。结果:4档光子束能量下治疗床薄、中、厚段位置穿透因子范围分别为0.956 6～1.000 0、0.955 4～1.000 0和0.954 8～1.000 0,薄中段在6 MV-FFF120°时最小,厚段在6 MV-FFF 130°时最小。与0°照射相比,180°照射6 MV-FFF、6 MV、10 MV-FFF和10 MV X射线表面剂量从30.6%、24.1%、18.3%和14.1%分别增加到95.4%、93%、83%和79.6%。结论:治疗床的存在减少肿瘤剂量、增加表面剂量,FFF模式较FF影响更大,在治疗计划系统中加入虚拟床减小了治疗床引起的剂量学影响。     

电离室矩阵用于加速器质量保证：X射线

目的：探讨利用二维电离室矩阵MatriXX进行医用直线加速器质量保证的方法及可靠性。方法：在点剂量的质量保证中。将MatriXX系统在特制水箱中测得的数据与O．6CC电离室在标准水箱中的剂量测量值作比较,从而定出Ma．triXX的校准系数．以此来校准射线的输出量和能量。在面剂量的质量保证中,用MatriXX测量医用加速器射线野的对称性、平坦度以及辐射野的大小及中心轴偏离．将测量结果与RFA300三维水箱扫描结果及控制台显示数值进行比较分析。结果：用MatriXX加有机玻璃板可准确快捷地完成对射线输出量和能量的校准。用MatriXX所测射野的对称性和平坦度及射线野大小与RFA300水箱的测量数据一致。结论：MatriXX系统进行加速器的质量保证简便可靠。     

二维电离室矩阵测量射野边缘

目的:探讨用二维电离室矩阵测量放射野边缘应注意的事项.材料与方法:使用IBA公司的MATRIXX二维电离室矩阵对VARIAN公司的23EX加速器的射野进行测量.把电离室矩阵水平放置在加速器床面上,电离室中心处于等中心位置,SAD=100 cm.射野大小从4.0 cm×4.0 cm变到16 cm×16 cm.每射野出束50 MU,记录测量结果.用OmniPro I'mRT(1.5)软件分析测量数据.结果:在X1、X2、Y1、Y2四个边半影大小随射野大小变化而呈现波浪式周期性变化,相邻波峰波谷间距为(3.79±0.25)mm.波谷底部平坦,平区宽度为(2.3±0.3)mm,波峰顶部也平坦,平区宽度为(2.2±0.2)mm.波蜂波谷高度相差为(4.0±0.1)mm.结论:用二维电离室矩阵测量射野半影时应充分考虑电离室矩阵的位置对测量结果的影响,对于同一个射野,由于摆放矩阵位置不同,可引起4mm的差别.改变矩阵位置,从不同位置重复测量,可减小矩阵位置的影响.     

Elekta Infinity直线加速器治疗床对放疗剂量的影响

目的:研究Elekta Infinity直线加速器治疗床在常用X射线能量下对放疗剂量的影响。方法:将圆柱体模体分别置于碳纤维主治疗床、延长板以及治疗床与延长板衔接处正中,旋转机架,分别让6和10 MV高能X射线穿过治疗床,利用指形电离室测量固体水中间的绝对剂量,得出不同角度下的剂量分布,并计算治疗床对X射线的衰减因子。结果:治疗床与延长板衔接处在120°和240°两个机架角处的剂量衰减因子在6和10 MV两种治疗模式下分别达到了36.02%和36.01%以及30.46%和30.63%,而当机架角为140°~220°时,衔接处与主治疗床的剂量衰减因子相近,在6与10 MV能量下的剂量衰减因子平均值及标准差分别为2.56%±0.49%和2.14%±0.39%以及2.55%±0.48%和1.95%±0.41%,机架角由180°增大或减小时两处的剂量衰减均呈上升趋势,二者均在120°和240°附近达到最大;6和10 MV两种能量下延长板在该角度区间的剂量衰减因子平均值及标准差分别为1.55%±0.24%和1.07%±0.25%,并在115°和245°附近达到最大值,剂量衰减因子分别为4.08%和3.97%以及3.20%和3.34%。结论:后斜野主体部分在主治疗床与衔接处对剂量的衰减低于3%,在延长板处对剂量的衰减小于2%,但在120°和240°附近以及115°和245°附近3处位置的剂量衰减会达到最大,需在计划系统中考虑床的影响;此外,主治疗床与延长板衔接处在120°和240°附近对剂量的衰减急剧增大,不适合作为治疗区域,在治疗病人时需注意避免将靶区移到该区域。     

用蒙特卡洛方法模拟和评价电离室矩阵探测器的定位灵敏度

目的:由于阵列式平板探测器内每个电离室单元探测器结构和尺寸的差异,构成了不同厂家生产的探测器阵列在放射治疗质量控制中的地位,各自的优势和不足。本文通过Monte Carlo(MC)模拟对不同面积的准直器遮挡入射束所形成的剂量场分布,并和实验测量的结果进行比较,用于评价不同厂家生产的方形探测器电离室矩阵与圆形探测器阵列的对照射野定义的位置灵敏度。方法:用BEAMnrc软件对电子直线加速器机头建模并模拟6 MV X射线的注量场分布,得到PHASE SPACE(相空间)文件,用DOSXYZnrc计算水模体中探测器的剂量分布范围与实际被照射面积的对应关系,从而评价PTW公司的SEVEN29电离室矩阵(方形探测器)与IBA公司的MatriXX电离室矩阵(圆形探测器)对位置的探测敏感度。结果和结论:PTW公司的SEVEN29和IBA公司的MatriXX两种阵列中单个探测器的定位灵敏度在2%的误差范围内基本一致,在放射治疗中凡是涉及对位置的精度检测的操作过程中,这两种电离室矩阵都可以任意选用,其位置的空间定位精度在1 mm以下。     

A method of beam-couch intersection detection

At the time of treatment planning it would be useful to know whether part of the treatment beam passes through the patient/couch support assembly before it passes through the patient. In the previous work of Yorke, the range of gantry angles leading to beam-couch intersection was found as a function of couch translation for symmetric field sizes and for zero couch rotation. Yorke's method has been extended to include couch rotation, dual independent jaws, and multi-leaf collimator (MLC) field shapes. In addition, the new method is also applicable in the situation of the couch top located above the isocenter. For a clinically treatable, 20 x 20 cm field configuration in a linac, the range of gantry angles leading to beam-couch intersection are different by 6.7 degrees for a couch rotation angle of 25 degrees when compared to no couch rotation. The new method agrees with data within the setup and measurement uncertainties for a variety of field sizes including an oval shaped MLC field, and various couch locations, couch, and collimator rotation angles.     

A computerized remote table control for fast on-line patient repositioning: implementation and clinical feasibility

A computerized remote control for a Siemens ZXT treatment couch was implemented and its characteristics were investigated to establish its feasibility for on-line setup corrections, using portal imaging. Communication with the table was obtained by connecting it via a serial line to a work station. The treatment couch enables "goto" commands in the three main directions and around the isocenter. The accuracy of the movements after giving such a command was checked and the time for each movement was recorded. First, the movements into a single direction were studied (range of -4 to +4 cm and -4 degrees to +4 degrees). Each command was repeated four times. Second, the table was moved into the three main directions simultaneously. For this experiment a clinically relevant three-dimensional (3-D) normal distribution of shifts was used [N = 200, standard deviation (SD) 5 mm in the three main directions]. This latter experiment was done twice: without and with rotations (a distribution with SD 1 degrees). During the first experiment, with shifts into one direction, no systematic deviations were found. The overall accuracy of the shifts was 0.6 mm (1 SD) in each direction and 0.04 degrees (1 SD) for the rotations. The time required for a translation ranged between 4 and 13 s and for the rotation between 8 and 20 s. The second experiment with the 3-D distribution of setup errors yielded an error in the 3-D vector length equal to 0.96 mm (1 SD), independent of rotations. Shifts were performed in less than 11 s for 95% of the cases without rotations. When rotations were also performed, 95% of the movements finished in less than 16 s. In conclusion, the table movements are accurate and enable on-line setup corrections in daily clinical practice.     

An analysis of the treatment couch and control system dynamics for respiration-induced motion compensation

Sophisticated methods for real-time motion compensation include using the linear accelerator, MLC, or treatment couch. To design such a couch, the required couch and control system dynamics need to be investigated. We used an existing treatment couch known as the Hexapod to gain insight into couch dynamics and an internal model controller to simulate feedback control of respiration-induced motion. The couch dynamics, described using time constants and dead times, were investigated using step inputs. The resulting data were modeled as first and second order systems with dead time. The couch was determined to have a linear response for step inputs < or = 1 cm. Motion data from 12 patients were obtained using a skin marker placed on the abdomen of the patient and the marker data were assumed to be an exact surrogate of tumor motion. The feedback system was modeled with the couch as a second-ordersystem and the controller as a first order system. The time constants of the couch and controller and the dead times were varied starting with parameters obtained from the Hexapod couch and the performance of the feedback system was evaluated. The resulting residual motion under feedback control was generally <0.3 cm when a fast enough couch was simulated.     

Megavoltage x-ray skin dose variation with an angle using grid carbon fibre couch tops

It is well known that a skin dose from high-energy x-ray radiation varies with the angle of beam incidence or the presence of a radiotherapy linear accelerator couch top material. This note investigates changes produced to the skin dose from a Varian carbon fibre grid couch top at differing angles of incidence for 6 MV x-rays as is often the case clinically. Results have shown that the skin dose can easily be measured using an EBT Gafchromic film whereby the delivered skin dose can be quantified to a high level of spatial resolution, not easily achieved with other skin dose detectors. Results have shown a significant increase in the skin dose specifically at the point of a cross-sectional carbon fibre grid. Values in % of the skin dose increased from approximately 27% (an open area within a 10 cm x 10 cm field) up to 55% (same field size) at the centre of the carbon fibre mesh strip (0 degrees incidence). This is compared to 19% of the skin dose for an open field of a 10 cm x 10 cm beam without the couch material present. At larger angles similar effects occur with values changing from 52% to 75% (60 degrees , 10 cm x 10 cm) in the open area and under the grid, respectively. This produces a wave effect for the skin dose. The average skin dose magnitude increases with the angle of incidence of the beam, ranging from 37.5% to 66% from 0 degrees to 60 degrees (10 x 10 cm), respectively. The symmetric wave nature of the skin dose profile skews to deliver an increased dose on the posterior side of the carbon fibre grid as the angle of incidence increases. Simulated fractional dose delivery on a phantom has shown that over 30 fractions the wave nature of the delivered skin dose is minimized due to the random nature of most patient positioning on the treatment couch. However, some variations are still present as the ratio of the open to grid area is approximately 4:1 and the dose spread is not necessarily completely averaged during a typical fractionated radiotherapy treatment. As such, if the treatment type results in a more rigorously positioned patient on the treatment couch, the wave nature of skin dose delivery may need to be taken into account.     

全脑全脊髓转床半野照射技术的临床应用

目的：介绍一种通过转床、半野进行全脑全脊髓照射的技术。方法：模拟定位时首先设颈胸脊髓野：机架角O°,小机头0°,床角0°,SSD=100cm,野长40cm,野宽4cm～5cm,同时在体膜上标记射野上界（B点）和下界（C点）,然后设全脑野：使用半束左右两野对穿照射,机架角90°或270°,小机头11.3°或348．7°,床角0°,SAD=100cm,Y1=0,X和Y2取包括颅骨外1cm,使射野X方向中心线在透视下与B点重合,最后设腰骶脊髓野：以C点为中心使用半束照射,机架角11.3°,小机头O°,床角90°,SSD=100cm,X2=0,Y和X1取包括腰骶直至S4。同时使用Kodak-Ec-film胶片、固体水模体以及MatriXX系统在加速器治疗机上模拟射野进行射野衔接点的几何和剂量验证,并观察12例使用该技术投照期间患者的放疗反应。结果：颈胸段脊髓野与全脑野衔接点以及颈胸段脊髓野与下位脊髓野衔接点处射野边界清晰锐利,未见射野间分离和重合现象,等剂量线基本平滑,未见明显的凹陷和凸出现象,12例患者都完成全脑全脊髓的照射计划,未见明显严重的放疗反应。结论：全脑全脊髓转床半野照射技术做到了射野间的无缝衔接,方法简便,值得临床推广应用。     

测量治疗床、SBRT体架及DAVID系统造成的剂量衰减

目的:通过测量6 MV的X线经过治疗床、SBRT体架和DAVID系统后的剂量衰减,为计划设计时的剂量补偿提供参考数据。方法:加速器与固体水之间无任何器材,源皮距(SDD)为100 cm,出束照射100 MU,利用电离室测量固体水下深度5 cm的剂量,作为基准剂量。同样条件下测量治疗床、SBRT体架和DAVID系统以不同组合在水下深度5 cm的剂量。结果:射线穿过治疗床剂量衰减了3.08%,经过治疗床和SBRT体架衰减了13.10%,经过治疗床、SBRT体架和DAVID系统衰减了13.10%,经过治疗床和DAVID系统衰减了10.88%,经过DAVID系统衰减8.07%。结论:在没有安装DAVID系统时,只有经过治疗床和SBRT体架的射线需要进行剂量补偿。安装了DAVID系统时,所有的射线束都需要计算DAVID系统对射线的衰减,经过治疗床和SBRT体架的射线还需要计算这两个器材对剂量的衰减。不同情况下衰减比例不同,需要补偿的剂量也不同。     

Evaluation of mechanical precision and alignment uncertainties for an integrated CT/LINAC system

A new integrated CT/LINAC combination, in which the CT scanner is inside the radiation therapy treatment room and the same patient couch is used for CT scanning and treatment (after a 180-degree couch rotation), should allow for accurate correction of interfractional setup errors. The purpose of this study was to evaluate the sources of uncertainties, and to measure the overall precision of this system. The following sources of uncertainty were identified: (1) the patient couch position on the LINAC side after a rotation, (2) the patient couch position on the CT side after a rotation, (3) the patient couch position as indicated by its digital readout, (4) the difference in couch sag between the CT and LINAC positions, (5) the precision of the CT coordinates, (6) the identification of fiducial markers from CT images, (7) the alignment of contours with structures in the CT images, and (8) the alignment with setup lasers. The largest single uncertainties (one standard deviation or 1 SD) were found in couch position on the CT side after a rotation (0.5 mm in the RL direction) and the alignment of contours with the CT images (0.4 mm in the SI direction). All other sources of uncertainty are less than 0.3 mm (1 SD). The overall precision of two setup protocols was investigated in a controlled phantom study. A protocol that relies heavily on the mechanical integrity of the system, and assumes a fixed relationship between the LINAC isocenter and the CT images, gave a predicted precision (1 SD) of 0.6, 0.7, and 0.6 mm in the SI, RL and AP directions, respectively. The second protocol reduces reliance on the mechanical precision of the total system, particularly the patient couch, by using radio-opaque fiducial markers to transfer the isocenter information from the LINAC side to the CT images. This protocol gave a slightly improved predicted precision of 0.5, 0.4, and 0.4 mm in the SI, RL and AP directions, respectively. The distribution of phantom position after CT-based correction confirmed these results. Knowledge of the individual sources of uncertainty will allow alternative setup protocols to be evaluated in the future without the need for significant additional measurements.     

碳素纤维床CT值对头部肿瘤放疗计划剂量分布的影响

目的:定量分析碳素纤维床CT值对头部肿瘤放疗计划剂量分布的影响。方法:在Varian Eclipse 13.6计划系统中建立9种不同CT值的碳素纤维床和均匀圆柱水模体模型,并将圆柱水模体放置于碳素纤维床中间,在10 cm[×]10 cm射野下,采用6 MV X射线机架在0°~180°之间以10°为间隔行等中心照射,计算不同CT值的碳素纤维床的吸收剂量差异系数。选取头部肿瘤患者15例,以Eclipse计划系统提供的默认CT值碳素纤维床为基础,设计放疗计划,并将该计划保存为模板计划。随后将模板计划移植至其余8种不同CT值的碳素纤维床图像中,不进行通量优化,重新计算剂量分布。记录9种不同CT值碳素纤维床计划的D2%、D50%、D98%、CI、HI以及GI。结果:在-700 HU至-300 HU内,随着Panel Surface CT值的增加,吸收剂量差异系数逐渐减小;在-1 000 HU至-900 HU内,随着Panel Interior CT值的增加,吸收剂量差异系数逐渐增大。默认CT值的碳素纤维床计划与其他8种碳素纤维床计划的D2%、D50%、D98%,以及GI差异具有统计意义（P<0.05）,而HI则无统计学差异（P>0.05）。结论:物理师在设计放疗计划时,应根据实测治疗床的CT值构建碳素纤维床模型。     

应用提高分辨率的MatriXX检测等中心偏移的方法简介

目的:以检测等中心在X方向的偏移示例,介绍使用提高分辨率之后的MatriXX检测等中心偏移的方法。方法:在确保MLC的leaf bank关于collimator中心轴旋转对称,且MatriXX中心与等中心的偏差已知的基础上,将gantry和collimator的角度都设为0°,治疗床向X正方向每移动1 mm测量1次5 cm×5 cm照射野100 MU的剂量分布曲线,共7次移动治疗床,测量8组数据,然后将这8组数据叠加为一组复合数据,得到gantry和collimator角度为0°、5 cm×5 cm照射野100 MU时MatriXX在X方向分辨率为1 mm的剂量分布曲线。同样的方法测量得到将gantry角度设为180°时相对应的剂量分布曲线,然后使用OmniPro I’mRT软件对比分析这两个profile,得出等中心在X方向的偏移值。结果:等中心的偏移值为1.8 mm。结论:提高分辨率之后的MatriXX能够检测出等中心的偏移值;等中心的偏移会导致病人接受剂量出现偏差,而这种偏差可以通过调整Elekta Synergy MLC的leaf bank关于gantry旋转中心轴对称和计划设计中设置collimator与couch角度为0°来克服;等中心的偏差使得gantry角度在90°和270°附近照射野的平面剂量偏差非常大。因此,不建议计划设计中设置gantry角度在90°和270°附近的照射野,也不建议选用MatriXX或者其他平面探测器做照射野gantry角度集中在90°和270°附近的病人计划验证。