Enhancing Precision in Radiotherapy Delivery: Validating Monte Carlo Simulation Models for 6 MV Elekta Synergy Agility LINAC Photon Beam Using Two Models of the GAMOS Code

The most crucial requirement in radiation therapy treatment planning is a fast and accurate treatment planning system that minimizes damage to healthy tissues surrounding cancer cells. The use of Monte Carlo toolkits has become indispensable for research aimed at precisely determining the dose in radiotherapy. Among the numerous algorithms developed in recent years, the GAMOS code, which utilizes the Geant4 toolkit for Monte Carlo simula-tions, incorporates various electromagnetic physics models and multiple scattering models for simulating particle interactions with matter. This makes it a valuable tool for dose calculations in medical applications and throughout the patient’s volume. The aim of this present work aims to vali-date the GAMOS code for the simulation of a 6 MV photon-beam output from the Elekta Synergy Agility linear accelerator. The simulation involves mod-eling the major components of the accelerator head and the interactions of the radiation beam with a homogeneous water phantom and particle information was collected following the modeling of the phase space. This space was po-sitioned under the X and Y jaws, utilizing three electromagnetic physics mod-els of the GAMOS code: Standard, Penelope, and Low-Energy, along with three multiple scattering models: Goudsmit-Saunderson, Urban, and Wentzel-VI. The obtained phase space file was used as a particle source to simulate dose distributions (depth-dose and dose profile) for field sizes of 5 × 5 cm2 and 10 × 10 cm2 at depths of 10 cm and 20 cm in a water phantom, with a source-surface distance (SSD) of 90 cm from the target. We compared the three electromagnetic physics models and the three multiple scattering mod-els of the GAMOS code to experimental results. Validation of our results was performed using the gamma index, with an acceptability criterion of 3% for the dose difference (DD) and 3 mm for the distance-to-agreement (DTA). We achieved agreements of 94% and 96%, respectively, between simulation and experimentation for the three electromagnetic physics models and three mul-tiple scattering models, for field sizes of 5 × 5 cm2 and 10 × 10 cm2 for depth-dose curves. For dose profile curves, a good agreement of 100% was found between simulation and experimentation for the three electromagnetic physics models, as well as for the three multiple scattering models for a field size of 5 × 5 cm2 at 10 cm and 20 cm depths. For a field size of 10 × 10 cm2, the Penelope model dominated with 98% for 10 cm, along with the three multiple scattering models. The Penelope model and the Standard model, along with the three multiple scattering models, dominated with 100% for 20 cm. Our study, which compared these different GAMOS code models, can be crucial for enhancing the accuracy and quality of radiotherapy, contributing to more effective patient treatment. Our research compares various electro-magnetic physics models and multiple scattering models with experimental measurements, enabling us to choose the models that produce the most reli-able results, thereby directly impacting the quality of simulations. This en-hances confidence in using these models for treatment planning. Our re-search consistently contributes to the progress of Monte Carlo simulation techniques in radiation therapy, enriching the scientific literature.

Accuracy of the Small Field Dosimetry Using the Acuros XB Dose Calculation Algorithm within and beyond Heterogeneous Media for 6 MV Photon Beams

Purpose: The dosimetric accuracy of the recently released Acuros XB advanced dose calculation algorithm (Varian Medical Systems, Palo Alto, CA) is investigated for single radiation fields incident on homogeneous and heterogeneous geometries, as well as for two arc (VMAT) cases and compared against the analytical anisotropic algorithm (AAA), the collapsed cone convolution superposition algorithm (CCCS) and Monte Carlo (MC) calculations for the same geometries. Methods and Materials: Small open fields ranging from 1 × 1 cm2 to 5 × 5 cm2 were used for part of this study. The fields were incident on phantoms containing lung, air, and bone inhomogeneities. The dosimetric accuracy of Acuros XB, AAA and CCCS in the presence of the inhomogeneities was compared against BEAMnrc/DOSXYZnrc calculations that were considered as the benchmark. Furthermore, two clinical cases of arc deliveries were used to test the accuracy of the dose calculation algorithms against MC. Results: Open field tests in a homogeneous phantom showed good agreement between all dose calculation algorithms and MC. The dose agreement was +/?1.5% for all field sizes and energies. Dose calculation in heterogenous phantoms showed that the agreement between Acuros XB and CCCS was within 2% in the case of lung and bone. AAA calculations showed deviation of approximately 5%. In the case of the air heterogeneity, the differences were larger for all calculations algorithms. The calculation in the patient CT for a lung and bone (paraspinal targets) showed that all dose calculation algorithms predicted the dose in the middle of the target accurately;however, small differences (2% - 5%) were observed at the low dose region. Overall, when compared to MC, the Acuros XB and CCCS had better agreement than AAA. Conclusions: The Acuros XB calculation algorithm in the newest version of the Eclipse treatment planning system is an improvement over the existing AAA algorithm. The results are comparable to CCCS and MC calculations especially for both stylized and clinical cases. Dose discrepancies were observed for extreme cases in the presence of air inhomogeneities.

Calculation of photon attenuation coefficient and dose rate in concrete with the addition of SiO_2 and MnFe_2O_4 nanoparticles using MCNPX code and comparison with experimental results

One of the most important safety features of nuclear facilities is the shielding material used to protect the operating personnel from radiation exposure. The most common materials used in radiation shielding are concretes. In this study, a Monte Carlo N-Particle eXtended code is used to calculate the gamma-ray attenuation coefficients and dose rates for a new concrete material composed of MnFe_2O_4 nanoparticles, which is then compared with the theoretical and experimental results obtained for a SiO_2 nanoparticle concrete material. According to the results, the average relative differences between the simulations and the theoretical and experimental results for the linear attenuation coefficient(l) in the SiO_2 nanoparticle materials are 6.4% and 5.5%, respectively. By increasing the SiO_2 content up to 1.5% and the temperature of MnFe_2O_4 up to 673 K, l is increased for all energies. In addition, the photon dose rate decreases up to 9.2% and3.7% for MnFe_2O_4 and SiO_2 for gamma-ray energies of0.511 and 1.274 MeV, respectively. Therefore, it was concluded that the addition of SiO_2 and MnFe_2O_4 nanoparticles to concrete improves its nuclear properties and could lead to it being more useful in radiation shielding.

Analysis of Dose Calculation Accuracy in Cone Beam Computed Tomography with Various Amount of Scattered Photon Contamination

Cone-beam computed tomography (CBCT) images have inaccurate CT numbers because of scattered photons. Thus, quantitative analysis of scattered photons that affect an electron density (ED) curve and calculated doses may be effective information to achieve CBCT-based radiation treatment planning. We quantitatively evaluated the effect of scattered photons on the accuracy of dose calculations from a lung image. The Monte Carlo method was used to calculate CBCT projection data, and we made two calibration curves for conditions with or without scattered photons. Moreover, we applied cupping artifact correction and evaluated the effects on image uniformity and dose calculation accuracy. Dose deviations were compared with those of conventional CT in conventional and volumetric intensity modulated arc therapy (VMAT) planning by using γ analysis and dose volume histogram (DVH) analysis. We found that cupping artifacts contaminated the scattered photons, and the γ analysis showed that the dose distribution was most decreased for a scattered photon ratio of 40%. Cupping artifact correction significantly improved image uniformity;therefore, ED curves were near ideal, and the pass rate results were significantly higher than those associated with the scattered photon effect in 65.1% and 78.4% without correction, 99.5% and 97.7% with correction, in conventional and VMAT planning, respectively. In the DVH analysis, all organ dose indexes were reduced in the scattered photon images, but dose index error rates with cupping artifact correction were improved within approximately 10%. CBCT image quality was strongly affected by scattered photons, and the dose calculation accuracy based on the CBCT image was improved by removing cupping artifacts caused by the scattered photons.

Radiation dose enhancement in skin therapy with nanoparticle addition: A Monte Carlo study on kilovoltage photon and megavoltage electron beams

AIM To investigated the dose enhancement due to the incorporation of nanoparticles in skin therapy using the kilovoltage(k V) photon and megavoltage(MV) electron beams. Monte Carlo simulations were used to predict the dose enhancement when different types and concentrations of nanoparticles were added to skin target layers of varying thickness.METHODS Clinical k V photon beams(105 and 220 k Vp) and MV electron beams(4 and 6 MeV), produced by a Gulmay D3225 orthovoltage unit and a Varian 21 EX linear accelerator, were simulated using the EGSnrc Monte Carlo code. Doses at skin target layers with thicknesses ranging from 0.5 to 5 mm for the photon beams and 0.5 to 10 mm for the electron beams were determined. The skin target layer was added with the Au, Pt, I, Ag and Fe2O3 nanoparticles with concentrations ranging from 3 to 40 mg/m L. The dose enhancement ratio(DER), defined as the dose at the target layer with nanoparticle addition divided by the dose at the layer without nanoparticle addition, was calculated for each nanoparticle type, nanoparticle concentration and target layer thickness.RESULTS It was found that among all nanoparticles, Au had thehighest DER(5.2-6.3) when irradiated with kV photon beams. Dependence of the DER on the target layer thickness was not significant for the 220 k Vp photon beam but it was for 105 kV p beam for Au nanoparticle concentrations higher than 18 mg/m L. For other nanoparticles, the DER was dependent on the atomic number of the nanoparticle and energy spectrum of the photon beams. All nanoparticles showed an increase of DER with nanoparticle concentration during the photon beam irradiations regardless of thickness. For electron beams, the Au nanoparticles were found to have the highest DER(1.01-1.08) when the beam energy was equal to 4 MeV, but this was drastically lower than the DER values found using photon beams. The DER was also found affected by the depth of maximum dose of the electron beam and target thickness. For other nanoparticles with lower atomic number, DERs in the range of 0.99-1.02 were found using the 4 and 6 MeV electron beams.CONCLUSION In nanoparticle-enhanced skin therapy, Au nanoparticle addition can achieve the highest dose enhancement with 105 k Vp photon beams. Electron beams, while popular for skin therapy, did not produce as high dose enhancements as k V photon beams. Additionally, the DER is dependent on nanoparticle type, nanoparticle concentration, skin target thickness and energies of the photon and electron beams.

The Effect of the Size of Radiotherapy Photon Beams on the Absorbed Dose to an Al_2O_3 Dosimeter

The effect of the size of radiotherapy photon beams on the absorbed dose to an Al2O3 dosimeter was investigated using the Monte Carlo method. The EGSnrc/DOSRZnrc program code was used to simulate the absorbed dose to the Al2O3 dosimeter, as well as the absorbed dose to water at the corresponding position in the absence of the dosimeter. The incident beams were 60Co γ and 6 MV with a different beam radius ranging from 0.1 cm to 2 cm. Results revealed that the absorbed dose ratio factor depends on the size of the incident photon beam. When the radius of the incident beam is smaller than that of the dosimeter, the absorbed dose ratio factor decreases as the incident beam size increases. The absorbed dose ratio factor reaches its minimum when the radius of the incident beam is almost the same as that of the dosimeter. When the radius of the incident beam is larger than that of the dosimeter, the absorbed dose ratio factor increases as the incident beam size increases. The maximum difference among these absorbed dose ratio factors can be up to 14% in 60Co γ beams and 23% in 6 MV beams. However, when the size of the incident beam is much larger than that of the dosimeter, the effect of the incident beam size on the absorbed dose ratio factor becomes quite small. The maximum discrepancy between the absorbed dose ratio factors and the average value is not more than 1%.

Study of the Photon Flux and the Dose Rate in the Vicinity of a 60Co Gamma Irradiator

The present work presents an overview of the study of some dosimetric quantities in the vicinity of the Tunisian Gamma Irradiation Facility. Firstly, we have confirmed our previous calculation of the photon flux and the dose rates, using a simulation with GEANT 4. A good agreement between calculation and simulation was obtained, which well confirmed the modeling of the CNSTN extended source by a pencil-like source. Secondly we have determined the isodose curves in the vicinity of the irradiator using a straightforward calculation. Finally, we have presented many comments for some published work concerning the methods used to determine these dosimetric quantities.

基于机械性能检测分析VitalBeam型直线加速器输出剂量的稳定性评估及故障案例分析

基于机械性能检测(MPC)系统,分析医用直线加速器VitalBeam输出剂量的长期稳定性。采集2021年1月至2023年12月北京朝阳医院VitalBeam型医用直线加速器的500组日常自检数据,分析其剂量输出偏差的改变趋势和稳定性状态。通过MPC检测和数据分析,6MVX射线的射线剂量输出变化为(0.53±0.85)%,射线均匀度变化为(0.54±0.15)%,射线中心偏移变化为(0.15±0.07)mm,均在误差允许的范围内,该医用直线加速器6MV光子束剂量输出稳定可靠,满足临床治疗需要,MPC检测可用于加速器的日检质量控制。

The Dosimetric Effects of Different Beam Energy on Physical Dose Distributions in IMRT Based on Analysis of Physical Indices

This work aimed at evaluating the effect of 6- and 10-MV photon energies on intensity-modulated radiation therapy (IMRT) treatment plan outcome in different selected diagnostic cases. For such purpose, 19 patients, with different types of non CNS solid tumers, were selected. Clinical step-and-shoot IMRT treatment plans were designed for delivery on a Siemens Oncor accelerator with 82 leafs;multi-leaf collimators (MLCs). To ensure that the similarity or difference among the plans is due to energy alone, the same optimization constraints were applied for both energy plans. All the parameters like beam angles, number of beams, were kept constant to achieve the same clinical objectives. The Comparative evaluation was based on dose-volumetric analysis of both energy IMRT plans. Both qualitative and quantitative methods were used. Several physical indices for Planning Target Volume (PTV), the relevant Organs at Risk (OARs) as mean dose (Dmean), maximum dose (Dmax), 95% dose (D95), integral dose, total number of segments, and the number of MU were applied. Homogeneity index and conformation number were two other evaluation parameters that were considered in this study. Collectively, the use of 6 MV photons was dosimetrically comparable with 10 MV photons in terms of target coverage, homogeneity, conformity, and OAR savings. While 10-MV plans showed a significant reduction in the number of MUs that varied between 4.2% and 16.6% (P-value = 0.0001) for the different cases compared to 6-MV. The percentage volumes of each patient receiving 2 Gy and 5 Gy were compared for the two energies. The general trend was that 6-MV plans had the highest percentage volume, (P-value = 0.0001, P-value = 0.006) respectively. 10-MV beams actually decreased the integral dose (from average 183.27 ± 152.38 Gy-Kg to 178.08 ± 147.71 Gy-Kg, P-value = 0.004) compared with 6-MV. In general, comparison of the above parameters showed statistically significant differences between 6-MV and 10-MV groups. Based on the present results, the 10-MV is the optimal energy for IMRT, regardless of the concerns about a potential risk of radiation-induced malignancies. It is recommended that the choice to treat at 10 MV be taken as a risk vs. benefit as the clinical significance remains to be determined on case by case basis.

Energy Dependence of the New Gafchromic EBT3 Film:Dose Response Curves for 50 KV, 6 and 15 MV X-Ray Beams

Purpose: To study and compare the dose response curves of the new GafChromic EBT3 film for megavoltage and kilovoltage x-ray beams, with different spatial resolutions. Methods: EBT3 films (lot#A101711-02) were exposed to each x-ray beam (6 MV, 15 MV, and 50 kV) at 7 dose values (50-3200 cGy). Each film piece was scanned three consecutive times in the center of Epson 10000XL flatbed scanner in 48-bit color at two separate spatial resolutions of 75 and 300 dpi. The data were analyzed using ImageJ and, for each scanned image, a region of interest (ROI) of 2 × 2 cm2 at the field center was selected to obtain the mean pixel value with its standard deviation in the ROI. For each energy, dose value and spatial resolution, the average net optical density (netOD) and its associated uncertainty were determined. The Student’s t-test was performed to evaluate the statistical differences between the net OD/dose values of the three energy modalities, with different color channels and spatial resolutions. Results and Discussion: The dose response curves for the three energy modalities were compared in three color channels. Weak energy dependence was found. For doses above 100 cGy, no statistical differences were observed between 6 and 15 MV beams, regardless of spatial resolution and color channel. However, statistical differences were observed between 50 kV and the megavoltage beams. The degree of energy dependence (from MV to 50 kV) was found to be a function of color channel, dose level, and spatial resolution. Conclusions: The dose response curves for GafChromic EBT3 films were found to be weakly dependent on the energy of the photon beams from 6 MV to 15 MV. For very low energy photon (e.g. 50 kV), variation of more than 11% due to the energy-dependence is observed, depending on the absorbed dose, spatial resolution and color channel used.

Eclipse计划系统计算网格大小对脑胶质瘤VMAT计划影响分析

目的比较Eclipse计划系统计算网格大小对脑胶质瘤容积旋转调强治疗(Volume Modulated Arc Therapy,VMAT)计划质量的影响,为临床诊疗提供依据。方法回顾性选取2021年9月至2022年6月我院收治的行VMAT计划的胶质瘤患者33例,在优化参数相同的条件下,对所有患者分别用1.25、2.50、5.00 mm计算网格设计3组VMAT计划(1.25 mm组、2.50mm组、5.00mm组)。比较3组VMAT计划的靶区剂量学参数[临床靶区(Clinical Tumor Volume,CTV)、计划靶区(Planning Target Volume,PTV)]、机器跳数、危及器官受量和计划优化时间。结果5.00 mm组躯干D_(max)、CTV D_(max)均显著高于1.25 mm组和2.50 mm组,1.25 mm组的PTV D_(min)、CTV D_(min)均显著高于2.50 mm组和5.00 mm组。3组危及器官受量和机器跳数比较差异均无统计学意义(P>0.05)。1.25 mm组与2.50 mm组、5.00 mm组的CTV D_(min)、PTV D_(min)靶区剂量相对偏差较大,其他靶区剂量参数相对偏差较小。1.25 mm组与2.50 mm组、5.00 mm组的左侧晶体、左侧视神经、右侧视神经的相对偏差较大。1.25 mm组与2.50 mm组、5.00 mm组的机器跳数相对偏差均较小。1.25 mm组计划优化时间明显短于2.50mm组和5.00mm组。结论脑胶质瘤放射治疗中,Eclipse计划系统选用不同计算网格会引起VMAT PTV及危及器官产生剂量方面的差异。从计划质量与优化时间综合考虑,建议采用2.50 mm的计算网格来进行VMAT计划设计,但需注意小网格会导致体积较小的危及器官受量增高,因此选取小网格优化时,建议适当增大危及器官限量权重来降低危及器官受量。

基于GPU加速的筒串卷积剂量计算算法的准确性验证

目的:验证基于GPU加速的筒串卷积剂量计算算法的准确性以及临床可行性。方法:以调强放射治疗计划系统软件KylinRay-TPSe为平台,分别根据中华人民共和国医药行业标准YY 0775、YY/T 0889以及部分临床例题对基于GPU加速的筒串卷积剂量计算算法进行测试。在YY 0775标准测试中,对特定照射几何条件下水模体中规定计算点的剂量进行计算并与剂量参考值进行比较。在YY/T 0889标准测试中,对调强计划中固体水模体上特定位置的点剂量和面剂量进行计算并与实验测量得到的剂量值进行比较。在临床例题测试中,采用头颈部、胸腹部、盆腔部肿瘤临床病例各5例,从Pinnacle^(3)计划系统中导出患者的治疗计划信息并导入到KylinRay-TPSe中,通过调用基于GPU加速的筒串卷积剂量计算算法对患者体内的剂量分布进行计算,提取计算结果中靶区和危及器官的剂量学参数,与Pinnacle^(3)的计算结果进行t检验,并比较等中心面的2Dγ通过率和3Dγ通过率。结果:基于GPU加速的筒串卷积剂量计算算法满足YY 0775标准和YY/T 0889标准的准确性要求。在临床例题测试中,计划靶区和危及器官中的各项剂量学参数与Pinnacle^(3)计算结果的差异均无统计学意义(P>0.05),所有例题等中心面的2Dγ通过率均在95.1%以上,3Dγ通过率均在95.0%以上。结论:基于GPU加速的筒串卷积剂量计算算法具有较高的准确性,满足临床使用的要求。

放射治疗中医用直线加速器光子能量合成方法

目的:分析一种利用高低两档能量光子拟合任意中间能量光子的方法,并与现有方法进行对比。方法:百分深度剂量曲线(PDD)和离轴剂量分布曲线(OCR)是影响光子射束数据模型计算精度的两个重要特征参数。使用Varian Truebeam直线加速器模型中金标准射束数据6和15 MV射束的PDD和OCR数据,采用最小二乘拟合方法拟合中间能量10 MV射束,与金标准数据10 MV射束数据比较分析,并与其他拟合方法进行对比,证明该方法的可行性和有效性。基于三维仿真水模体数据和不同肿瘤部位的实际病例数据实验,进一步验证合成能量方法的准确性。结果:相比只考虑PDD数据的能量拟合方法,本研究方法得到的合成能量10 MV与金标准数据10 MV光子束相比,各尺寸射野下PDD的均方根误差有所增加,但均小于1%,而OCR的均方根误差明显减小(特别是20 cm以上的射野),均小于0.5%。三维仿真水模体数据和实际患者数据测试例实验结果优于只考虑PDD数据的能量拟合方法。结论:利用PDD和OCR数据合成光子能量方法的效果较仅使用PDD数据的方法更好,合成能量光子与实际10 MV光子之间PDD和OCR差异较小,基于三维仿真水模体和实际病例数据的不同放疗技术计划三维剂量分布的一致性很高,拟合能量光子可代替实际能量光子用于临床治疗。

加速器辐射质测量方法的比较分析

针对加速器高能光子辐射质的不同测量方法,在剂量比(D20/D10)通过公式计算法和组织模体比(TPR20,10)直接实验法的基础上,提出了定剂量率和定剂量的测量方法.在中国计量科学研究院加速器实验室分别对6 MV、10 MV、25 MV光子的辐射质进行测量.实验结果表明:在测量加速器辐射质时,采用定剂量法比定剂量率法不确定度明显变小;采用定剂量法时,6 MV、10 MV、25 MV采用公式法计算的值比实际测量值分别偏小0.27％、0.31％、0.35％,采用剂量率法进行修正后和此结果一致.

利用EGS4计算固体电离室的吸收剂量与光子注量的转换因子

利用蒙特卡罗程序 EGS4 ,针对几种特定的γ光子谱 ,计算了特定形状的 Li F固体电离室中空腔辐射敏感元件 L i FTLD的吸收剂量 -光子注量转换因子 ;计算结果表明 ,该转换因子的不确定度主要取决于谱的不确定度 ;通过对单能光子源的蒙特卡罗计算结果与解析公式计算结果的比较 ,证明该方法是可靠的 。

应用Geant4计算光子外照射对人体产生的有效剂量

在Geant4中构建ORNL程式化混合模体,应用此模体计算不同能量下平行光子入射的人体有效剂量。计算结果以吸收剂量与空气比释动能比值的形式呈现。计算结果与ICRP74值进行了对比验证。

医用高能光子水吸收剂量测量规范TRS-277与TRS-398比较

随着吸收剂量测量及其量值溯源理论和技术的发展,国际原子能机构先后发布了TRS-277、TRS-398号报告,规范了高能光子水中吸收剂量的测量,以满足临床应用时不确定5.0%(k=2)的要求。文中依据两个报告,从量值溯源方式、测量方法、参数引用、修正因子的来源及其确定等方面,比较了两个报告在高能光子水中吸收剂量测量中的使用差异;同时指出了应用TRS-398号报告能进一步减少测量结果的不确定度,对开展精确放射治疗具有指导意义。

CT能量成像技术原理和应用

目前CT能量成像技术已经在临床工作实践中被逐渐广泛应用起来,但由于CT能量成像技术与传统的CT成像技术有较大不同,所以本文基于目前应用最为广泛的双源法CT能量成像技术对CT能量成像技术的原理和应用进行述评。期望有助于读者对CT能量成像技术有总体的认识和了解。

医用电子加速器高能光子水吸收剂量溯源

采用直接法测量医用电子加速器高能光子水吸收剂量,与我国现行的从空气比释动能转化为水吸收剂量间接法测量的结果进行比较。结果表明,两种方法测量结果相差1%以内,同时用传递比较法进行了验证。证明我国基于加速器光子水吸收剂量基准而建设的水吸收剂量溯源体系是可行的,为我国水吸收剂量直接测量提供依据。

用蒙特卡罗方法计算光子外照射对人体产生的有效剂量

采用雌雄同体的成人人体模型和蒙特卡罗方法(MCNP4C)计算了环境γ射线外照射对人体产生的有效剂量。为了便于比较,计算中选用了ICRP 74号出版物中给出的20种不同的γ光子能量以及从前向后照射和从后向前照射两种辐照几何源。对计算结果进行比较发现,MCNP4C程序计算得到的结果与ICRP 74号出版物中给出的结果非常吻合。