金属植入物对放射治疗剂量影响的研究

目的：测量金属内固定支架对放射治疗剂量的影响,对采用金属内固定的肿瘤患者放射治疗提供剂量修正的临床数据。方法：按照测量条件,将带有金属内固定支架的体模在螺旋CT下进行扫描,层厚为5mm,图像通过LANTIS网络传输系统传人放射治疗计划系统（treatment planning system,TPS）中进行模拟计算。按照相同条件,分别用6MV和15MVX线照射,用热释光剂量仪和FAMER型电离室对钛镍合金支架界面以及界面上下一定深度分别测量,并与放射治疗计划系统计算结果比较。结果：实际测量与TPS计算存在一定误差,实测值明显大于TPS计算值,支架前表面的误差最大可达3．9％（6MV）和6．6％（15MV）,支架后表面的误差最大为2．8％（6MV）和6．3％（15MV）,距表面距离越远,误差越小。结论：镍钛合金支架患者放射治疗时,实际测量剂量比TPS计算剂量要大,有可能增加放射性损伤。TPS计算过程中,虽然对金属物进行了密度修正,但仍存在一定误差,有必要在制订放疗计划时对照射剂量进行修正。     

金属食管支架对放射治疗剂量分布的影响

目的测量网状自扩金属食管支架对放射线引起的空腔效应及散射效应对放射治疗剂量分布的影响,为食管癌支架置入术后放射治疗的剂量修正提供依据.方法应用模拟食管癌网状自扩金属支架置入术后放射治疗的体模,分别应用60Co γ射线和直线加速器的8 MV X射线进行照射,使用薄窗电离室、热释光剂量仪分别对不锈钢合金支架及钛镍合金支架空腔的界面及界面下一定深度进行了对比测量,并用治疗计划系统对单纯空腔情况下百分深度剂量的变化进行了模拟计算与测量结果进行对照.结果射野7 cm×15 cm 60Co治疗机照射支架前点、后点与无支架均匀水模对应点剂量增加值不锈钢支架分别为1.8%和3.2%,钛镍合金支架分别为1.7%和2.9%.直线加速器的8 MV X射线照射支架前点、后点与无支架均匀水模对应点剂量增加值不锈钢支架分别为1.5%和2.8%,钛镍合金支架分别为1.4%和0.9%.射线经过支架空腔后形成二次建成效应,剂量增加的峰值达7.6%. 结论网状金属食管支架对放射线的散射效应造成的剂量增加<2%,支架空腔形成的二次建成效应,剂量增加>5%. 建议实际放射治疗时须对支架的空腔效应修正计算剂量.     

放射治疗计划系统剂量跳数计算的独立验证

背景与目的:保证放射治疗计划剂量计算的准确性是放射治疗质量保证的重要内容.本实验验证一种第三方计算软件和3D-TPS的MU计算精度,测试和探讨放射治疗计划独立验证的可行性和可靠性.方法:在TPS中使用均匀模体,根据IAEA第430号技术报告设计开野、挡块野、楔形野和MLC不规则野等测试计划.(1)对上述各计划以给定MU执行照射.用电离室在体模内测量执行剂量并将测量结果输入商业QA软件进行MU计算,验证独立计算的精度.(2)分别以指形电离室在直线加速器上直接测量和QA独立计算软件两种方法验证上述计划的执行结果,比较两种验证方法的结果差异.结果:(1)所有计划的独立验证软件计算结果与实际测量的偏差为(0.1±0.9)%,同时有挡块和楔形板的射野两者差异最大(为2.0%).(2)所有测试计划的TPS计算相对于独立验算软件计算的MU偏差为(0.6±1.0)%(-0.8%～2.8%);TPS计算与实际测量的相对剂量偏差为(-0.2+1.7)%(-3.9%～2.9%).结论:所测试的独立验证软件的计算误差在临床可接受范围.各测试计划的独立验算与实际测量验证的总体差异不大.该独立验算软件可作为TPS计划质量保证的一种有效工具.     

面罩对不同射线治疗剂量影响的探讨

目的：测量在光子线及电子线照射下面罩对治疗剂量的影响。方法：采用PIW Marcus 23343型平行板电离室在专用的有机玻璃模体（PMMA）中测量光子线建成区别剂量的变化情况，采用Bruce等介绍的经验公式对测量结果进行修正，采用三维水箱测量电子线射野中心轴百分深度剂量，并利用平行板电离室对特定深度进行验证，结果：加上面罩后，8MV光子线建成区剂量有明显增加，近表面处相对增加约25％左右，8、12和15MeV的电子线的中心轴百分深度剂量曲线则普遍前移。结论：对于光子线主要考虑的是近表面建成区剂量的改变；对电子线则要考虑由于百分深度量前移而可能影响治疗靶区的最小剂量。三维适放射治疗中要注意治疗治疗计划系统（TPS）的计算结果是否考虑面罩对治疗剂量的影响。     

调强放射治疗的物理剂量验证

目的：检测调强适形放射治疗（Intensity modulatet radiation therapy,IMRT)的剂量误差,探索IMRT的质量控制和质量保证的措施和方法。方法：（1）用体模治疗计划移植的方法对43例IMRT治疗计划的照射区以电离室作实际物理剂量测量,以验证治疗计划系统剂量计算的准确性,照射设备的可靠性和稳定性,修正IMRT治疗剂量误差和确定其剂量精度范围。（2）选取计划照射区内剂量梯度变化较大处进行重复摆位测量剂量,推算和验证由于摆位误差可能造成的剂量误差。结果：（1）与计划剂量比较,实际测量剂量的相对误差范围为-0.74%-4.98%并近似正态分布,平均误差为2.38%。标准差为1.39%,标准误为0.21%。全部43例的剂量误差均在5%以内。（2）实际测量的剂量梯度变化与计划剂量梯度一致,全部计划中的最大梯度值为15%/mm。在该处重复摆位测量的最在与最小值的相对差别为1.97%。结论：用体模计划移植测量方法能有效检验IMRT计划计算和执行的误差,可作为每个病人治疗前的剂量验证常规方法;IMRT治疗精度的保证需要优于1mm的额外精确摆位。     

IGRT加速器剂量验证过程中出现的问题及解决方案

目的:我们对我科最新投入临床使用的IGRT加速器系统(包括CMS治疗计划系统、网络、加速器等)进行剂量验证的实际测量,检查治疗计划系统剂量计算的准确性。方法:根据治疗计划系统制定的验证计划,通过网络传输至加速器,使用现场剂量仪等对验证计划剂量进行实际测量,并对实际测量数据进行系统分析,检查分析,确定其剂量准确性范围、误差及产生的原因。结果:经过对实际测量结果的分析、比较,发现实际测量结果与TPS计算剂量误差>2%。经过对整个系统的检查、分析,最终确定误差偏大的原因是TPS在剂量计算过程中将电离室等效为空气所致。结论:对于我们所使用的CMS治疗计划系统,凡是涉及到电离室的验证计划,在剂量计算过程中,电离室应等效为水。     

食管内置网状金属支架对放射治疗剂量的影响

目的：研究食管内置金属支架对放射治疗剂量的影响,以便在临床应用中进行适当修正。方法：采用热释光元件测量,测量探测器为国产Fj-427A热释光剂量仪,热释光元件为LiF(Mg,P,Cu)片状型剂量元件。分别测量两种（进口及国产）,食管内置网状金属支架及未放支架的石蜡体模,测量支架周围（即食管粘膜处）的剂量并与无支架时食管中心点的剂量进行比较。结果：国产支架单野垂直照射时沿射束方向,支架前点和后点对^60Co γ射线和416MV X射线剂量增加分别为16．2％和7．8％、15．4％和6．8％、12．8％和5．8％,进口支架单野垂直照射量增加分别为13．0％和7．0％及11．7％和6．0％,8．5％和3．2％;前后两野对穿照射剂量增加11．7％－24．0％,3个野交角照射支架周围（食管粘膜）均增加3．2％－16．2％。结论：置放食管网状金属支架后进行常规放射治疗时,单次剂量最好≤1．7Gy,前后对穿野照射时≤1．5Gy,建议使用直径＜1．5cm支架,选用3个野交叉照射。     

二维治疗计划系统在鼻咽癌设野和射线能量选择方面的应用

随着临床影像 CT、MRI检查的普及以及放射治疗设备的不断更新完善 ,治疗计划系统 (TPS)的推广应用 ,放射源的合理选择及照射野的优化已成为放射治疗医师所迫切关心的问题。我们以鼻咽癌为例 ,根据临床放射治疗设野要求以及临床剂量学四项基本原则 ,通过TPS系统的等剂量曲线图在鼻咽癌 CT定位片上的分布 ,来讨论鼻咽癌五野和四野设计的优劣和射线能量的选择 ,以提高肿瘤靶区照射剂量 ,减少正常组织照射剂量 ,供同仁们讨论参考。 (TPS软件为 :核通公司 PL ATO External BeamPlanning TPS version 1.8.1)1　材料与方法1.1　材料　根…     

应用密度填充及伪影消减技术提高带金属植入物患者IMRT剂量准确度研究

目的探讨提高带金属植入物患者放射治疗计划剂量计算准确度的方法。方法利用具有金属伪影消减技术的CT模拟机对插入金属棒的CIRS调强模体和8例椎体中植入了钢钉并接受放疗的患者进行扫描,在获得的常规CT图像、金属伪影消减技术CT图像及对其金属区域进行密度填充的图像上设计治疗计划。在模体中比较单个射野及IMRT计划的计算结果与剂量测量结果,同时对患者IMRT计划中金属植入物及其伪影对照射剂量产生的影响进行分析。结果基于常规CT图像的放疗计划中,射野入射路径未通过金属区域时,单个射野的剂量计算误差为3.85%,通过金属区域时射野计算误差范围达4.46%~74.11%。IMRT计划中存在入射路径通过金属区域的射野时,其误差可能超出临床可接受的范围,计算误差随这种射野所占剂量权重的增加而变大。当采用密度填充及伪影消减技术处理图像后,上述单个射野的计算误差分别为1.23%和0.89%~4.73%,IMRT计划的剂量误差为1.84%。若单独采用密度填充技术处理金属区域,IMRT计划的剂量误差为1.88%。基于常规CT图像的患者IMRT计划中,受金属植入物及其伪影的影响,实际靶区受到的最小剂量、平均剂量及处方剂量覆盖率较计划结果下降,危及器官剂量相近。结论基于常规CT图像的放疗计划中,入射路径通过金属区域的射野可能产生较大的剂量计算误差。如果植入的金属材料已知,在计划系统中对金属区域进行密度填充能有效提高计划的剂量计算准确度。伪影消减技术能显著改善图像质量,进一步减少剂量计算误差,对于配备这种功能的CT机进行带金属植入物患者的模拟定位时应作为常规技术。     

体内金属植入物对放疗剂量分布影响

目的 探讨放射野内金属植入物对其周围组织吸收剂量的影响.方法 将骨科内固定不锈钢板、钛合金板和相同大小条状肌肉分别置入尸体标本左侧股骨前侧,构建实验组与对照组模型.应用直线加速器6 MV X线照射,使用热释光剂量仪分别对不同内植物界面的吸收剂量进行测量,用治疗计划系统对有无金属植入物百分深度剂量变化进行模拟计算并与测量结果 比较.结果 6MVX线照射置入不锈钢板、钛合金板和条状肌肉时,入射面实际测量值分别为1.18 Gy±0.04 Gy、1.12 Gy±0.04 Gy和0.97 Gy±0.03 Gy(F=57.35,P<0.01),不锈钢板和钛合金板较条状肌肉相应位置吸收剂量分别增加了21.65%和15.46%;出射面实际测量值分别为0.87 Gy±0.03 Gy、0.90Gy±0.02 Gy和0.95 Gy±0.04 Gy(F=13.37,P<0.01),不锈钢板和钛合金板较条状肌肉相应位置点吸收剂量分别衰减了8.42%和5.26%.模拟计算钢板入射面1 cm范围内吸收剂量较条状肌肉明显增加,而钢板入射面1 cm以外范围影响<5%,出射面对剂量分布影响<2%.结论 金属植入物对放疗剂量分布存在明显影响,吸收剂量可产生5%～22%偏差;相同条件下不锈钢板对射线剂量分布影响较钛合金板明显.     

The influence of x-ray energy on lung dose uniformity in total-body irradiation

: In this study we examine the influence of x-ray energy on the uniformity of the dose within the lung in total-body irradiation treatments in which partial transmission blocks are used to control the lung dose.

: A solid water phantom with a cork insert to simulate a lung was irradiated by x-rays with energies of either 6, 10, or 18 MV. The source to phantom distance was 3.9 meters. The cork insert was either 10 cm wide or 6 cm wide. Partial transmission blocks with transmission factors of 50% were placed anterior to the cork insert. The blocks were either 8 or 4 cm in width. Kodak XV-2 film was placed in the midline of the phantom to record the dose. Midplane dose profiles were measured with a densitometer.

: For the 10 cm wide cork insert the uniformity of the dose over 80% of the block width varied from 6.6% for the 6 MV x-rays to 12.2% for the 18 MV x-rays. For the 6 cm wide cork insert the uniformity was comparable for all three x-ray energies, but for 18 MV the central dose increased by 9.4% compared to the 10 cm wide insert.

: Many factors must be considered in optimizing the dose for total-body irradiation. This study suggests that for AP/PA techniques lung dose uniformity is superior with 6 MV irradiation. The blanket recommendation that the highest x-ray energy be used in TBI is not valid for all situations.     

Half body radiotherapy: the use of computed tomography to determine the dose to lung

The complication of radiation pneumonitis is of major concern in upper half body irradiation. A CT-aided treatment planning system was utilized to study the variation in lung geometry and lung density and to determine the resultant dose variation within the corresponding treatment volumes. Twenty-three patients who were scheduled for upper half body irradiation, were studied with this CT-aided treatment planning system and a number of parameters were analyzed to determine the factors affecting the dose to lung. For healthy lungs, electron densities, relative to water, varied from 0.084 to 0.40; the average lung density was approximately 0.25. Using the equivalent tissue-air ratio method for dose calculation, the dose within lung increased from 10% to 24% in comparison with doses calculated on the basis of a homogeneous water like patient. This dose increase is dependant on patient thickness, lung thickness and lung density. The calculated doses were verified experimentally by thermoluminescent dosimetry in a human-like phantom for photon beam energies ranging from cobalt-60 to 25 MV x-rays. Agreement between the measured and calculated data was better than 3% in lung. A number of other dose computation procedures were found to be in error by more than ±10% in the determination of dose to the middle of lung. Some simplified procedures, which do not require a CT-aided treatment planning system, also were evaluated. The previously published dose complication curve for radiation pneumonitis now can be considered in terms of absolute dose to lung rather than the dose prescribed to unit density tissues.     

Linear array measurements of enhanced dynamic wedge and treatment planning system (TPS) calculation for 15 MV photon beam and comparison with electronic portal imaging device (EPID) measurements

INTRODUCTION.: Enhanced dynamic wedges (EDW) are known to increase drastically the radiation therapy treatment efficiency. This paper has the aim to compare linear array measurements of EDW with the calculations of treatment planning system (TPS) and the electronic portal imaging device (EPID) for 15 MV photon energy. MATERIALS AND METHODS.: The range of different field sizes and wedge angles (for 15 MV photon beam) were measured by the linear chamber array CA 24 in Blue water phantom. The measurement conditions were applied to the calculations of the commercial treatment planning system XIO CMS v.4.2.0 using convolution algorithm. EPID measurements were done on EPID-focus distance of 100 cm, and beam parameters being the same as for CA24 measurements. RESULTS: Both depth doses and profiles were measured. EDW linear array measurements of profiles to XIO CMS TPS calculation differ around 0.5%. Profiles in non-wedged direction and open field profiles practically do not differ. Percentage depth doses (PDDs) for all EDW measurements show the difference of not more than 0.2%, while the open field PDD is almost the same as EDW PDD. Wedge factors for 60 deg wedge angle were also examined, and the difference is up to 4%. EPID to linear array differs up to 5%. CONCLUSIONS: The implementation of EDW in radiation therapy treatments provides clinicians with an effective tool for the conformal radiotherapy treatment planning. If modelling of EDW beam in TPS is done correctly, a very good agreement between measurements and calculation is obtained, but EPID cannot be used for reference measurements.     

An Assessment of Dosimetric Characteristics of Inline 2.5 Mega Voltage Unflattened Imaging X-Ray Beam

Purpose: The aim of this work is to study the dosimetric parameters of newly introduced 2.5 MV imaging x-ray beam used as inline imaging to do setup verification of the patient undergoing radiation therapy. As this x-ray beam is in megavoltage range but comprises of a lower energy spectrum. It is essential to study the pros and cons of 2.5 MV imaging x-ray beam for clinical use.Methods: The mean energy was calculated using the NIST XCOM table through MAC. Profile analysis was done using RFA to understand the percentage depth dose, degree of unflatteness, symmetry, penumbra and out of field dose. Dose to skin for the 2.5 MV x-ray beam was analysed for field sizes 10x10 cm2, 20x20 cm2, 30x30 cm2. Leakage measurements for treatment head and at the patient plane were done using IEC 819/98 protocol. Finally, the spatial resolution and contrast were analyzed with and without patient scatter medium. Results: The MAC at 15 cm off-axis was found to be lower than that at the CAX. Similarly, there was a decrease in mean energy from 0.47 MV to 0.37 MV at 15 cm off-axis. The reduction of mean energy towards off-axis is lower than the other high energy MV x-ray beams. The tuned absolute dose of 1 cGy/MU is consistent and within < ±1 %. The relative output factors were found to be in correlation with Co-60. The beam quality of 2.5 MV x-ray beam was found to be 0.4771. The profile parameters like the degree of unflatness of the 2.5 x-ray beam were studied at 85 %, 90 %, 95 % lateral distances, and the penumbra at different depth and field sizes are higher than the 6 MV treatment beam. In addition, out of field dose also drastically increases to a maximum of up to 30 % laterally at 5cm at deeper depths. The skin dose increases from 48.51 % to 88.15 % from 6 MV to 2.5 MV x-ray beam for the field size 10x10 cm2. Also, the skin dose increases from 88.15 % to 91.78 % from the field size 10x10 cm2 to 30x30 cm2. Although the measured leakage radiation for 2.5 MV x-ray beam at the patient plane and other than patient planes are with the tolerance limit, an increase in exposure towards gantry side compared to other areas around treatment head and the patient plane may lead to more skin dose to head and chest while imaging pelvis region. The MLC transmission of 2.5 MV x-ray beam such as inter, intra and edge effect are 0.40 %, 0.37 % and 11% respectively. The spatial resolution of 2.0, 1.25 and 0.9 LP/mm was observed for KV, 2.5MV, and 6 MV x-ray beams. The spatial resolution and contrast of 2.5 MV x-ray beam are superior to 6 MV x-ray beam and inferior to KV x-rays. Conclusions: The 2.5 MV x-ray imaging beam is analysed in view of beam characteristics and radiation safety to understand the above-studied concepts while using this imaging beam in a clinical situation. In future, if 2.5MV x-ray beam is used for treatment purpose with increased dose rate, the above-studied notions can be incorporated prior to implementation.     

Total body irradiation, toward optimal individual delivery: dose evaluation with metal oxide field effect transistors, thermoluminescence detectors, and a treatment planning system

PURPOSE: To predict the three-dimensional dose distribution of our total body irradiation technique, using a commercial treatment planning system (TPS). In vivo dosimetry, using metal oxide field effect transistors (MOSFETs) and thermoluminescence detectors (TLDs), was used to verify the calculated dose distributions. METHODS AND MATERIALS: A total body computed tomography scan was performed and loaded into our TPS, and a three-dimensional-dose distribution was generated. In vivo dosimetry was performed at five locations on the patient. Entrance and exit dose values were converted to midline doses using conversion factors, previously determined with phantom measurements. The TPS-predicted dose values were compared with the MOSFET and TLD in vivo dose values. RESULTS: The MOSFET and TLD dose values agreed within 3.0% and the MOSFET and TPS data within 0.5%. The convolution algorithm of the TPS, which is routinely applied in the clinic, overestimated the dose in the lung region. Using a superposition algorithm reduced the calculated lung dose by approximately 3%. The dose inhomogeneity, as predicted by the TPS, can be reduced using a simple intensity-modulated radiotherapy technique. CONCLUSIONS: The use of a TPS to calculate the dose distributions in individual patients during total body irradiation is strongly recommended. Using a TPS gives good insight of the over- and underdosage in a patient and the influence of patient positioning on dose homogeneity. MOSFETs are suitable for in vivo dosimetry purposes during total body irradiation, when using appropriate conversion factors. The MOSFET, TLD, and TPS results agreed within acceptable margins.     

Accuracy of out-of-field dose calculation of tomotherapy and cyberknife treatment planning systems: A dosimetric study

PurposeLate toxicities such as second cancer induction become more important as treatment outcome improves. Often the dose distribution calculated with a commercial treatment planning system (TPS) is used to estimate radiation carcinogenesis for the radiotherapy patient. However, for locations beyond the treatment field borders, the accuracy is not well known. The aim of this study was to perform detailed out-of-field-measurements for a typical radiotherapy treatment plan administered with a Cyberknife and a Tomotherapy machine and to compare the measurements to the predictions of the TPS.Materials and methodsIndividually calibrated thermoluminescent dosimeters were used to measure absorbed dose in an anthropomorphic phantom at 184 locations. The measured dose distributions from 6 MV intensity-modulated treatment beams for CyberKnife and TomoTherapy machines were compared to the dose calculations from the TPS.ResultsThe TPS are underestimating the dose far away from the target volume. Quantitatively the Cyberknife underestimates the dose at 40 cm from the PTV border by a factor of 60, the Tomotherapy TPS by a factor of two. If a 50% dose uncertainty is accepted, the Cyberknife TPS can predict doses down to approximately 10 mGy/treatment Gy, the Tomotherapy-TPS down to 0.75 mGy/treatment Gy. The Cyberknife TPS can then be used up to 10 cm from the PTV border the Tomotherapy up to 35 cm.ConclusionsWe determined that the Cyberknife and Tomotherapy TPS underestimate substantially the doses far away from the treated volume. It is recommended not to use out-of-field doses from the Cyberknife TPS for applications like modeling of second cancer induction. The Tomotherapy TPS can be used up to 35 cm from the PTV border (for a 390 cm³ large PTV).     

宫颈癌三维适形调强放疗剂量分布特性研究

目的研究宫颈癌调强放疗(IMRT)和三维适形放疗(3D-CRT)时靶区及其周围正常组织受照剂量的差异。方法用WiMRT三维适形调强放疗计划系统分别进行6~9个照射角度的3D-CRT和IMRT计划设计,肿瘤量45Gy,计算出正常组织和靶区的剂量-体积直方图以及所需照射的总跳数,并根据10cm×10cm射野外漏射线和散射线剂量率的测量值,估算3D-CRT和IMRT放疗时射野外正常组织所受漏射线和散射线剂量。结果照射野数和照射角度一致,IMRT时膀胱、直肠、阴道所受平均剂量分别只有3D-CRT时的19.5%(29.3/150.3)、64.5%(538.0/833.0)和61.0%(1553.6/2546.3),靶区平均受照剂量略高于3D-CRT。IMRT病人射野外正常组织所受散射线和漏射线剂量约为3D-CRT病人的1.5倍。结论宫颈癌IMRT时射野外正常组织受漏射线和散射线照射剂量较高,但射野内靶区和邻近器官剂量分布优于3D-CRT。     

Surface Dose Measurements in Clinical Photon Beams

Surface dose measurements have been made with different dosemeters routinely used in clinical practice such as thermoluminescence (TL) dosemeters of different thicknesses or Si-diodes. the results obtained are compared with surface dose measurements made with an extrapolation chamber. TL-dosemeters with a thickness of 0.13 mm are shown to be suitable for skin dose estimations and accurate within 5% if appropriate correction factors are applied. the measured dose obtained for ⁶⁰Co, 6 MV and 21 MV x-rays should, for these dosemeters, be multiplied by 0.82, 0.90 and 1.0 respectively to obtain the correct surface dose. Thicker dosemeters are inaccurate because they overestimate the surface dose inside the beam and underestimate it outside the beam and the deviation from the correct dose varies with irradiation geometry.