Dose distributions in SBRT of lung tumors: Comparison between two different treatment planning algorithms and Monte-Carlo simulation including breathing motions

In stereotactic body radiotherapy (SBRT) of lung tumors, dosimetric problems arise from: 1) the limited accuracy in the dose calculation algorithms in treatment planning systems, and 2) the motions with the respiration of the tumor during treatment.Longitudinal dose distributions have been calculated with Monte Carlo simulation (MC), a pencil beam algorithm (PB) and a collapsed cone algorithm (CC) for two spherical lung tumors (2 cm and 5 cm diameter) in lung tissue, in a phantom situation. Respiratory motions were included by a convolution method, which was validated. In the static situation, the PB significantly overestimates the dose, relative to MC, while the CC gives a relatively accurate estimate. Four different respiratory motion patterns were included in the dose calculation with the MC. A "narrowing" of the longitudinal dose profile of up to 20 mm (at about 90% dose level) is seen relative the static dose profile calculated with the PB.     

A comparison of Monte Carlo and Fermi-Eyges-Hogstrom estimates of heart and lung dose from breast electron boost treatment

PURPOSE: Electrons are commonly used in the treatment of breast cancer primarily to deliver a tumor bed boost. We compared the use of the Monte Carlo (MC) method and the Fermi-Eyges-Hogstrom (FEH) algorithm to calculate the dose distribution of electron treatment to normal tissues. METHODS AND MATERIALS: Ten patients with left-sided breast cancer treated with breast-conservation therapy at the University of California, San Francisco, were included in this study. Each patient received an electron boost to the surgical bed to a dose of 1,600 cGy in 200 cGy fractions prescribed to 80% of the maximum. Doses to the left ventricle (LV) and the ipsilateral lung (IL) were calculated using the EGS4 MC system and the FEH algorithm implemented on the commercially available Pinnacle treatment planning system. An anthromorphic phantom was irradiated with radiochromic film in place to verify the accuracy of the MC system. RESULTS: Dose distributions calculated with the MC algorithm agreed with the film measurements within 3% or 3 mm. For all patients in the study, the dose to the LV and IL was relatively low as calculated by MC. That is, the maximum dose received by up to 98% of the LV volume was < 100 cGy/day. Less than half of the IL received a dose in excess of 30 cGy/day. When compared with MC, FEH tended to show reduced penetration of the electron beam in lung, and FEH tended to overestimate the bremsstrahlung dose in regions well beyond the electron practical range. These differences were clinically likely to be of little significance, comprising differences of less than one-tenth of the LV and IL volume at doses > 30 cGy and differences in maximum dose of < 35 cGy/day to the LV and 80 cGy/day to the IL. CONCLUSIONS: From our series, using clinical judgment to prescribe the boost to the surgical bed after breast-conserving treatment results in low doses to the underlying LV and IL. When calculated dose distributions are desired, MC is the most accurate, but FEH can still be used.     

利用深度学习提升肺癌调强质子治疗笔形束剂量计算准确性

目的:质子笔形束(PB)剂量计算可实现快速剂量计算,但在处理组织不均匀度大的区域时误差较大,而蒙特卡洛(MC)剂量计算是最精准的方法但非常耗时;深度学习技术可以通过学习PB和MC剂量分布之间的差异,将剂量计算准确度从PB水平提高到MC水平。方法:基于HD U-Net神经网络,开发了一个可将肺癌调强质子治疗患者的PB剂量...     

Verifikation eines schnellen Monte-Carlo-Dosis-berechnungsverfahrens durch EGSnrc anhand der statistischen Separationsmethode

The recently developed XVMC code, a fast Monte Carlo (MC) algorithm to calculate the dose of photon and electron beams in treatment planning, was compared to EGSnrc, an enhanced version of the well-known EGS4 system. Because of the numerous and accurate verification measurements, this system can be considered as golden standard. The comparison was performed using phantoms consisting of water, lung tissue and bone. Dose profile and difference distributions showed good agreement within the accuracy requirements. Because deviations between the results of two MC algorithms are caused by systematic errors and statistical fluctuations, a separation method was used to quantify the systematic discrepancies. Using this method, it could be shown that there was good agreement between the threedimensional dose distributions, calculated with XVMC and EGSnrc, if maximum systematic deviation of 2% are accepted.     

A Monte Carlo approach for small electron beam dosimetry.

BACKGROUND AND PURPOSE: In treatments where it is necessary to conform the field shape yielding a very small effective beam area, dosimetry and conventional treatment planning may be inaccurate. The Monte Carlo (MC) method can be an alternative to verify dose calculations. A conjunctival mucosa-associated lymphoid tissues lymphoma is presented, to show the importance of an independent assessment in critical situations. MATERIALS AND METHODS: In this work, the MC technique has been employed using the program BEAM (based on EGS4 code). Electron beam simulation has been performed and the results have been compared with those obtained with films. The patient dose distribution has been obtained by two methods: the full Monte Carlo (FMC) simulation and a conventional planning system (PLATO). RESULTS: Concerning dosimetry, some differences have been observed in the comparison of profiles obtained with film and those obtained with the MC method. Moreover, significant differences were found in the patient isodose distribution between both calculation methods. CONCLUSIONS: The results highlight that, in treatments where small beams are needed, conventional dosimetry and planning systems have some limitations. Therefore, an independent and more accurate assessment, such as MC, would be desirable.     

153Sm-EDTMP治疗骨转移病例的三维剂量计算——蒙特卡罗和S因子计算方法的比较

背景与目的:个体化核素治疗的三维吸收剂量计算是目前核医学感兴趣的问题。基于三维功能成像和器质成像计算三维吸收剂量,现主要采用S因子计算方法、点源卷积计算方法和蒙特卡罗直接模拟计算方法。本研究比较蒙特卡罗和基于体素的S因子计算方法,探索核素治疗中三维吸收剂量的计算。方法:基于蒙特卡罗程序包EGS4构建的三维剂量计算程序,计算核素153Sm的体素S因子;对1例采用153Sm-EDTMP治疗的鼻咽癌骨转移患者,测量其注射药物0、0.5、2、3.5、5和6h后排尿的核素活度,通过测量数据进行拟合计算其累积活度;结合患者的SPECT/CT联合扫描融合图像,采用直接蒙特卡罗方法和S因子方法进行了三维吸收剂量计算。结果:吸收剂量计算结果表明:蒙特卡罗和S因子两种计算方法所给出的等剂量分布曲线基本相近,剂量分布主要集中在骨组织内。在两种计算方法下,最大剂量点剂量分别为3.92Gy和3.71Gy,相差5%左右。计算区域的剂量-体积直方图显示:D10(10%体积所包括的最高剂量)分别为2.14Gy和2.00Gy,相差7%;D20则分别为0.58和0.51Gy,相差14%左右。总体来说,S因子方法的计算结果相对于蒙特卡罗方法的计算结果小一些。结论:蒙特卡罗和S因子方法都能够基于核医学影像进行核素治疗三维剂量计算,S因子方法计算误差可能稍大,但不失为一种快捷的剂量评估方法。     

对金属植入物模体不同剂量计算方法研究

目的 分析比较含有金属植入物的12-bit和16-bit CT图像应用不同算法下剂量的差异。方法 将钛合金棒插入模体中,CT下进行扫描,重建图像得到12-bit和16-bit图像。通过网络传输到Monaco计划系统,设计一个0°的单野,分别用PB算法,CC算法和MC算法计算剂量分布;扩展CT-ED曲线,重新计算剂量。使用Matlab 8.3数据处理软件获取沿射野方向通过金属植入物中心点的深度剂量曲线,对比12-bit和16-bit图像不同算法的剂量分布曲线和距金属植入物入射面与出射面不同距离处的剂量差异。并使用指形电离室进行测量。结果 16-bit CT图像能准确读出金属植入物的CT值,扩展CT-ED曲线后,相对于MC算法,PB算法在金属植入物入射面的剂量降低了5.43%,而在出射面处剂量升高了25.56%,在出射面后方剂量比MC算法结果高。CC算法降低了金属植入物入射面的剂量达4.5%,出射面处的剂量降低了4.31%,在出射面后方降低的更多。MC算法的计算值与测量值最接近。结论 对含有金属植入物的放疗患者,使用16-bit CT图像并扩展治疗计划系统的CT-ED曲线,并利用MC算法可以提高剂量计算的精确度。     

IMCO(++)--a Monte Carlo based IMRT system

The application of intensity modulated radiotherapy (IMRT) to dose escalation in the target volume sets particular demands in terms of accuracy of dose calculation. Dose calculation errors due to approximations are compensated by the optimization algorithm, a procedure that ultimately leads to incorrect fluence modulation. Such inaccuracies affect particularly the dose distribution in areas with secondary electron disequilibrium. In case tissues heterogeneity predominates, conventional dose calculation methods (such as Pencil Beam) can produce relative errors up to more than 10%. The accuracy can be significantly improved by the application of a Monte-Carlo (MC) algorithm. This paper describes a MC-based inverse treatment planning algorithm (IMCO++), based on a non-iterative approach with a feedback-controlling process. The convergence behavior of IMCO++ was investigated and the used MC dose-calculation codes MMms and XVMC were compared by means of a heterogeneous phantom. IMCO++ plans were optimized in various phantoms. All plans showed conformity in terms of dose distribution of the target volume and dose reduction in risk organs (according to the requirements of the target parameter), as well as a very fast convergence of the algorithm (in less than 10 optimization steps).     

Development and clinical application of a fast superposition algorithm in radiation therapy.

BACKGROUND AND PURPOSE: Dose calculation algorithms play a central role for the optimization and verification of treatment plans in radiation therapy. Complex treatment techniques like intensity modulated radiotherapy (IMRT) require accurate and fast dose algorithms especially for clinical cases which involve severe tissue inhomogeneities. For these cases the standard dose engine in current treatment planning systems--the convolution of photon pencil beams--usually fails to predict the dose with the required accuracy. The role of more accurate but time consuming dose calculations like superposition algorithms or Monte Carlo simulations in clinical practice is under investigation at several therapy centers. PATIENTS AND METHODS: The paper presents the design, implementation and the first application of a superposition algorithm in a clinical setting at the German Cancer Research Center (DKFZ). It first describes in detail how the superposition algorithm is adapted to the dose delivery system at DKFZ in terms of standard dosimetric data. Then details of the implementation of the algorithm are given with a focus on various methods for the reduction of dose computation times. Next, the algorithm is evaluated in various experiments with dosimetric phantoms. These studies are employed for the development of time efficient sampling strategies of the elemental dose kernels. Finally, the algorithm is applied to dose calculations of clinical cases with tumors adjacent to lung tissue. RESULTS: Severe differences in dose coverage of the tumors and dose burden of the surrounding tissues in comparison to standard pencil beam calculations are observed. A standard 4-7 beam plan in a convenient dose grid (approximately 3 mm in each direction) is calculated in about 30 min on a Pentium 4 (1.9 GHz) applying the superposition algorithm described here.     

HDR后装治疗CT图像至IMRT CT图像变形配准算法研究

目的 研究将高剂量率(HDR)后装治疗CT图像至IMRT的CT图像变形配准及剂量叠加的方法。方法 对含施源器的HDR CT图像进行分割,通过求解Navier-Stokes方程实现对施源器区域收缩变形以去除施源器;然后再利用基于Demons的图像变形配准方法,将去除施源器后的CTHDR图像及其剂量变形至CTIMRT图像域,完成HDR-IMRT CT图像变形配准及剂量累加。结果 利用宫颈癌患者放疗期间CTHDR和CTIMRT图像和相应剂量分布图像对算法进行验证,结果表明相对于一般变形配准算法,本算法能有效消除HDR CT图像中施源器对变形配准影响,得到精确的HDR-IMRT累加剂量分布。结论 ART中对总剂量监测和评价可让医生根据患者实际受量,新优化放疗计划,以实现放射剂量的精确投照。本算法可有效实现宫颈癌患者HDR-IMRT剂量的精确累加,其精度能满足实际临床的需要。     

蒙特卡罗系统验证PBC和CCC算法精确度的临床研究

目的 运用蒙特卡罗系统验证PBC、CCC算法在肺癌放疗计划时的精确度。方法 使用Oncentra Masterplan TPS对本院2012—2013年间收治的24例肺癌患者分别进行PBC、CCC计算。设计2个IMRT计划和2个3DCRT计划,将计划的DICOM-RT文件导入蒙特卡罗系统进行剂量重建。配对t检验差异。结果 4个计划中无论是IMRT还是3DCRT计划CCC、PBC计算的靶区平均剂量与蒙特卡罗计算值的差别均随靶体积减小而增大(P=0.00、0.00、0.00、0.00),且IMRT计划比3DCRT的大(P=0.00、0.01)。IMRT计划中CCC计算的D_98%、D_95%、D_90%、D_50%、D_2%与蒙特卡罗计算值差别逐渐减小(P=0.00、0.00、0.00、0.00、0.00),上述现象同样出现在PBC算法中,但CCC计算的3DCRT计划中的不显著(P=0.18、0.08、0.62、0.08,0.97)。IMRT和3DCRT计划中,CCC算法高估了整个患侧肺剂量;PBC算法高估了患侧肺V₂₀(P=0.00、0.00),低估了患侧肺V₅(P=0.00、0.00),但3DCRT计划中V₁₀值相近(P=0.47)。结论 建议在肺癌放疗计划计算时使用精确度更高的算法而不使用PBC算法。蒙特卡罗比其他算法精度更高。     

High density dental materials and radiotherapy planning: comparison of the dose predictions using superposition algorithm and fluence map Monte Carlo method with radiochromic film measurements.

BACKGROUND AND PURPOSE: During radiotherapy planning high density dental materials create a major challenge in determining correct dose distribution inside patients with head-and-neck tumors. PATIENTS AND METHODS: In this work we investigated the absorbed dose distribution inside a solid water slab phantom with embedded high density material irradiated by a 6MV photon beam of field size 10x10cm. We evaluated the absorbed dose distribution with three different techniques: superposition algorithm, radiochromic film, and the fluence map Monte Carlo (FMMC) method. RESULTS: The results obtained with radiochromic film and FMMC were in good agreement (within +/-5% of the dose) with one another. The superposition algorithm, which is often considered superior to other commercially available dose calculation algorithms, produced appreciably less accurate results than FMMC. In particular, downstream from the high density cerrobend inhomogeneity the superposition algorithm predicts a higher dose than the measurement does by at least 10-16% depending upon the size of the inhomogeneity and the distance from it. Upstream of the high density inhomogeneities the superposition algorithm predicts a lower than measured dose due to its failure to predict the dose enhancement close to the inhomogeneity interface. CONCLUSIONS: The delivered dose downstream from a high density inhomogeneity would be significantly less than the prescribed dose calculated by the superposition algorithm. The FMMC method which is based on a hybrid of the superposition algorithm input fluence data and Monte Carlo can be a useful tool in predicting dose in the presence of high density (e.g. dental) materials.     

Postimplant dosimetry using a Monte Carlo dose calculation engine: a new clinical standard

PURPOSE: To use the Monte Carlo (MC) method as a dose calculation engine for postimplant dosimetry. To compare the results with clinically approved data for a sample of 28 patients. Two effects not taken into account by the clinical calculation, interseed attenuation and tissue composition, are being specifically investigated. METHODS AND MATERIALS: An automated MC program was developed. The dose distributions were calculated for the target volume and organs at risk (OAR) for 28 patients. Additional MC techniques were developed to focus specifically on the interseed attenuation and tissue effects. RESULTS: For the clinical target volume (CTV) D(90) parameter, the mean difference between the clinical technique and the complete MC method is 10.7 Gy, with cases reaching up to 17 Gy. For all cases, the clinical technique overestimates the deposited dose in the CTV. This overestimation is mainly from a combination of two effects: the interseed attenuation (average, 6.8 Gy) and tissue composition (average, 4.1 Gy). The deposited dose in the OARs is also overestimated in the clinical calculation. CONCLUSIONS: The clinical technique systematically overestimates the deposited dose in the prostate and in the OARs. To reduce this systematic inaccuracy, the MC method should be considered in establishing a new standard for clinical postimplant dosimetry and dose-outcome studies in a near future.     

XVMC – Schnelle Monte-Carlo-Dosisberechnung für die Bestrahlungsplanung bei Photonenstrahlung

A new Monte-Carlo (MC) algorithm for calculating photon beam dose distributions in radiation therapy has been developed which is faster than EGS4/P RESTA by a factor of 15 to 20. Therefore, a standard treatment plan can be calculated by MC in approximately 20 minutes on a single CPU Personal Computer (450 MHz Pentium II). This new XVMC code is based on the fast electron transport procedure of the Voxel-Monte-Carlo (VMC) for electron beams. Photon transport is taken into account by exponential attenuation, ray tracing, and photon interaction cross sections (Compton scattering, pair production). The required material properties (electron stopping and scattering powers, electron density, attenuation coefficients) are determined directly from a given density distribution. The accelerator head is modelled either by a point source with energy distribution (primary photons) including a scatter contribution or a phase space file generated by the BEAM MC code.XVMC has been compared to EGS4 and measurements. A beam parameter generation utility and an interface to commercial planning systems will allow the implementation of the code for clinical routine treatment planning.     

基于蒙特卡罗实现容积调强弧形治疗计划独立剂量验证的应用研究

目的 开发基于蒙特卡罗(MC)的验证平台实现容积调强弧形治疗(VMAT)计划的独立剂量验证。方法 利用EGSnrc/BEAMnrc构建Varian TrueBeam医用直线加速器的机头和准直器模型,并基于机头模型和自编程序搭建患者VMAT计划的独立剂量验证平台,通过平台模拟不同射野大小百分深度剂量(PDD)曲线和离轴比、两个不规则野以及头颈部、胸部和盆腔各1例患者剂量分布。比较不同射野大小PDD曲线和离轴比与蓝水箱测量结果差异,不规则射野与ArcCHECK实测的差异,再通过γ分析法、剂量体积直方图对比分析患者MC模拟剂量、计划系统计算剂量、ArcCHECK实测剂量之间差异,验证平台是否可用于独立剂量验证。结果 对4cm×4cm~40cm×40cm的PDD曲线和离轴比,MC模拟结果和测量结果一致性较好。不规则射野MC模拟结果与ArcCHECK实测相比,在3%/2mm、3%/3mm下γ通过率都在98.1%、99.1%以上;3例不同部位VMAT患者MC模拟剂量和ArcCheck实测剂量在3%/2mm、3%/3mm下γ通过率均好于93.8%、95.9%。通过三维γ分析计划系统计算剂量和MC模拟剂量在3%/3mm下鼻咽癌、肺癌、直肠癌的γ通过率分别为95.2%、98.6%、98.9%;在3%/2mm下依次为90.3%、95.1%、96.7%。结论 基于MC开发的验证平台模拟结果与实际测量结果一致性较好,其模拟结果更接近于患者体内真实剂量分布,初步结果显示可用于VMAT计划的精准独立剂量验证。     

Pretreatment photosensitizer dosimetry reduces variation in tumor response

Purpose: To compensate for photosensitizer uptake variation in photodynamic therapy (PDT), via control of delivered light dose through photodynamic dose calculation based on online dosimetry of photosensitizer in tissue before treatment. Methods and Materials: Photosensitizer verteporfin was quantified via multiple fluorescence microprobe measurements immediately before treatment. To compensate individual PDT treatments, photodynamic doses were calculated on an individual animal basis, by matching the light delivered to provide an equal photosensitizer dose multiplied by light dose. This was completed for the lower quartile, median, and upper quartile of the photosensitizer distribution. PDT-induced tumor responses were evaluated by the tumor regrowth assay. Results: Verteporfin uptake varied considerably among tumors and within a tumor. The coefficient of variation in the surviving fraction was found significantly decreased in groups compensated to the lower quartile (CL-PDT), the median (CM-PDT), and the upper quartile (CU-PDT) of photosensitizer distribution. The CL-PDT group was significantly less effective compared with NC-PDT (Noncompensated PDT), CM-PDT, and CU-PDT treatments. No significant difference in effectiveness was observed between NC-PDT, CM-PDT, and CU-PDT treatment groups. Conclusions: This research suggests that accurate quantification of tissue photosensitizer levels and subsequent adjustment of light dose will allow for reduced subject variation and improved treatment consistency.     

153Sm-EDTMP治疗多发骨转移瘤的剂量效应关系初步观察

Objective: To calculate the focus absorption dose of 153Sm-EDTMP with the Monte Carlo (MC) EGS4 method for treatment of bone metastases from nasopharyngeal carcinoma or breast cancer, and investigate the relationship between the focus absorption dose and painkilling effect of 153Sm-EDTMP. Methods: Four patients with multiple bone metastases from nasopharyngeal or breast carcinoma and suffered from grade Ⅳ bone pain were treated with radionuclide internal irradiation of 153Sm-EDTMP. The absorption dose and dose distribution of bone metastases and other targeted organs were calculated with MC EGS4 program based on the time-order SPECT/CT scanning and the measurement of the radioactivity in the urine accumulation. The release of bone pain and the improvement of life quality were observed. Results: Bone pain of the patients was significantly alleviated to grade Ⅱ for 3-4 weeks after internal 153Sm-EDTMP irradiation. The 3-dimensional absorption dose distribution image of bone metastases and targeted organs showed that the dose distribution in bone metastases was not asymmetrical. After injection of 0.65 × 37 MBq/kg 153Sm-EDTMP, the highest absorption dose in bone lesions was about 4.9-5.9 Gy, and the dose in the lesion margin was about 2.0 Gy. Using the highest dose as reference dose point, the relative absorption dose values of bone marrow, vertebra and sex organ near lesions were 0.48-1.1 Gy, 0.51-0.85 Gy, and 0.01-0.14 Gy, respectively. Conclusion: The absorption dose of bone metastases is significantly lower than treatment dose of 30 Gy after single irradiation of 153Sm-EDTMP. The painkilling effect is limited and in accordance with clinical observation.     

A quantitative evaluation of IMRT dose distributions: refinement and clinical assessment of the gamma evaluation.

BACKGROUND AND PURPOSE: Although intensity modulated radiotherapy (IMRT) is a step forward in comparison to conventional, static beam delivery, quality assurance is more complex and labour intensive, demanding detailed two-dimensional dosimetric verification. Regardless of the technique used for measuring the dose distribution, what is essential to the implementation of routine verification of IMRT fields is the efficient and accurate comparison of the measured versus desired dose distribution. In order to achieve a fast, yet accurate quantitative measure of the correspondence between measured and calculated dose, the theoretical concept of the gamma evaluation method presented by Low et al. (Med. Phys., 25 (1998) 656) was converted into a calculation algorithm, taking into account practical considerations related to the discrete nature of the data.MATERIALS AND METHODS: A filter cascade of multiple levels was designed to obtain fast and accurate comparison of the two dose distributions under evaluation. The actual comparison consists of classification into accepted or rejected datapoints with respect to user-defined acceptance criteria (dose difference and distance to agreement). The presented algorithm was tested on dosimetric images calculated and/or acquired by means of a liquid filled portal imaging device during the course of intensity modulated treatments of prostate cancer, including pre-treatment verification as well as verification during treatment. To assess its ability to intercept possible errors in dose delivery, clinically relevant errors were deliberately introduced into the dose distributions.RESULTS: The developed gamma filter method proves successful in the efficient comparison of calculated versus measured IMRT dose distribution. Secondly, intercomparison of dosimetric images acquired during different treatment sessions illustrate its potential to highlight variations in the dosimetric images. The simulated errors were unmistakably intercepted.CONCLUSIONS: The readily obtained gamma evaluation images are an easy tool for quality control of IMRT fields. To reduce the artefacts related to the discrete nature and limited resolution of the data, a fast and accurate filter cascade was developed, offering the possibility to use the gamma method for day to day evaluation of patient dosimetric portal images with or without comparison to a predicted portal dose distribution.     

用蒙特卡罗方法模拟实验体内金属植入物对放疗剂量分布影响

目的 用蒙特卡罗(MC)模拟实验体内植入金属物后的百分深度剂量变化。方法 用6MVX线照射水下 5 cm处0.4 cm厚金属植入物,对有无金属植入物百分深度剂量变化进行MC方法模拟实验并比较结果。结果 6MVX线照射置入不锈钢板、钛合金板比不用植入物时入射面剂量分别增加19.6％、15.7％,不锈钢板、钛合金板入射面0.3 cm以外影响＜1.5％。不锈钢板、钛合金板出射面剂量分别减少8.6％、8.2％,剂量影响＜1.5％时距离出射面1.2、0.9 cm。不锈钢板比钛合金板入射面剂量大3.9％,出射面剂量相似。结论 MC方法是一种能快捷、准确的计算方式,金属植入物对放疗剂量影响明显,相同条件下不锈钢对入射面剂量影响大于钛合金钢板。