MRI定位式全身3D适形放疗的临床应用及体会

目前,放射治疗的主要发展是立体定向放射外科（γ刀,X刀）和三维适形放射治疗（3D CRT）。后者可分为螺旋CT和MRI等多种定位方式。MRI与三维放疗计划系统（3D TPS）联用,其最大优点是通过eflim,可同时获得三维（SAG／TRA／COR）T1 W1、TzWz多层次图像,对于靶区（Tumor）GTV和CTV轮廓勾画的定位精确性明显优于CT,因此具有很高的临床应用价值。现将我们在临床上的一些应用体会总结如下,以供同行们参考。     

O.S.S浅谈

Oncology Support System是荷兰PHI LIPS公司O.S.S的全称。这是一台在Treatment Planning System(T.P.S治疗计划系统)基础上发展而成、辅助CT诊断、设计三维放射治疗的专用计算机系统。我院放射治疗科于84年完成了SL 75—20医用电子直线加速器、模拟定位机、O.S.S等设备的安装     

宫颈癌调强放射治疗的剂量验证分析

目的:通过总结比较Eclipse和Xio两个治疗计划系统对宫颈癌调强放疗剂量验证的结果,分析评价宫颈癌调强放疗在临床应用上剂量的准确性。方法:分别用固体水模和二维电离室矩阵Mapcheck、FC65-G指形电离室在定位螺旋CT上进行扫描,断层数据通过网络传输到Eclipse和Xio两个治疗计划系统中建立验证模体。选取2013年1月至5月在本院24例宫颈癌调强治疗患者,在两个TPS(Treatment Planning Systems)上将宫颈癌调强放疗计划移植到模体上,用IBA公司的DOSE1、FC65-G指形电离室模体和Nuclear公司的二维电离室矩阵Mapcheck模体在加速器下进行点剂量和面剂量的采集。结果:Eclipse系统的12位患者随机选取24个照射野3 mm 3%面剂量的γ通过率均值为98.8%,Xio系统的12位患者随机选取24个照射野3mm3%面剂量γ通过率均值为97.7%,二者比较差别有统计学意义(P0.01)。Eclipse系统的12位患者84个照射野点剂量的误差的均值为1.2417%,Xio系统的12位患者84个照射野点剂量的误差均值为2.4892%,二者比较差别具有统计学意义(P0.01)。结论:Eclipse和Xio两个治疗计划系统都可以应用于宫颈癌临床调强放疗,但Eclipse系统的准确性优于Xio系统。     

略谈CT设备的选择

我国于1979年引进第一台颅脑CT应用于临床后,由于其良好的诊断效果,受到医生和患者的重视和欢迎。据有关部门统计,1986年末全国已装备CT 201台,平均每个省(市)6.9台。但仍远远满足不了临床诊断的需要,目前仍有许多医院正积极筹措资金,申请购买CT。可是,CT毕竟是价格昂贵的精密医疗设备,是列入国家控制进口的重大技术装备。以全身CT来说,每台价格从数十万至百万美元之间,头颅CT也需十几万美元。这就要求选购CT时,不仅要     

CT图像质量控制

一、目的 CT的影像质量的好坏直接关系到病变组织的显示程度。高质量的CT图像提供可靠的病灶信息。低劣的影像质量,不仅不能正确反映出病变组织结构,相反甚至引起误诊、漏诊。图像质量是放射学家和工程技术人员十分关心的问题,也是购买新设备首先要考虑的问题之一,因此严格控制CT扫描仪的质量至关重要。定期进行CT质量评估,使设备处于最佳运行状态。     

影像引导对乳腺癌调强放射治疗精度的影响

目的：分析在乳腺癌图像引导放射治疗（IGRT）过程中,图像引导对于放射治疗的精确度的影响;同时观察图像引导放射治疗的毒性反应及放射治疗近期的治疗效果。方法：搜集2012年1月-2013年2月间,于哈尔滨医科大学附属第三医院放疗科收治的乳腺癌患者25例。使用医科达SynergyTM锥形束CT（CBCT）进行治疗前扫描,通过图像引导放射治疗技术对25例患者进行误差纠正,调整后行调强放疗。患者在进行放疗前,用锥形柬CT对射野的偏差进行校正,其偏差利用锥形束CT图像与计划螺旋CT图像进行手动匹配,在X、Y、Z三个方向上进行调整。根据误差调整治疗床位置后治疗。对急性放射性反应采用RTOG5级评价标准进行评价：急性放射性皮肤反应、急性放射性肺损伤及急性放射性心脏损伤。结果：25例乳腺癌患者治疗前经锥形束CT扫描采集的图像与计划参考图像比较在X、Y、Z方向上平均误差分别为0．429±1．683mm、0．431±1．728mm、0．583±2．041mm：摆位误差纠正后,误差值分别为：0．068±0．429、0．019±0．438、0．158±0．697,调整后摆位误差控制在1mm之内进行治疗。放疗后2周急性皮肤反应为0级23例、1级2例;4周为0级21例、1级4例。无急性放射性肺损伤及心脏损伤的病例出现。结论：目前调强放疗是乳腺癌临床放射治疗的重要手段,图像引导放射治疗的应用能够使放疗精度显著提高。     

基于多孔小波融合的PET/CT 图像增强及其评价

目的:为解决融合图像视觉效果增强与量化信息损失之间的矛盾,本文提出一种基于非降采样的多孔小波(àtrous wavelet)分解的PET/CT图像融合方法,使得融合图像既有利于肿瘤诊断又能用于放疗靶区勾画和放射性定量分析。方法:对PET和CT图像分别进行多孔小波分解,以包含肿瘤目标的适当大小的感兴趣区域的清晰度为目标函数,采用Nelder-Mead算法对PET和CT图像高频分解系数之比进行优化获得最终的融合系数,使融合图像充分增加解剖学信息的同时又尽量保持PET图像原有的局部和整体灰度信息。结果:融合图像质量评价表明,本文方法能将有价值的PET功能信息与精确的CT解剖信息结合在一起,并克服传统小波融合损失图像量化信息的不足。结论:基于多孔小波融合的PET/CT图像既能用于肿瘤诊断,又能同时用于肿瘤学放射性计算和适形放疗计划制定等量化研究。     

植物细胞的肌醇磷脂信息传递系统

本文就（1）肌醇磷脂信息传递系统在植物中的存在,（2）肌醇磷脂的代谢途径、特点,（3）肌醇磷脂信息传递系统在外界刺激与生理生化反应之间的联系作用三个方面的研究进展进行介绍,并讨论这一领域研究中存在的问题和遇到的困难。     

谈谈课堂教学表情的反馈调控

世界著名的植物生理学家季米良捷夫说的好“教师不是传声筒,把书本的东西由口头传达出来;也不是照相机,把现实复呈出来,而是艺术家、创造者”。教师的教学不可能有僵化呆板的模式,因为他的教学对象是活生生的人,经常在变化,永远是新的。教师如果“举一隅”而没有觉察学生并不能“以三隅反”,还是絮絮不止地说教,便徒劳而无功。课堂教学是教师依据课时计划把浓缩了的编码信息,在有限的时间最大限度地向学生传递的过程,它是整个教学过程中的中心环节,是提高教学质量的关键所在,而善于“察言观色”——课堂的驾驭,是保证信息疏通的首要环节,所以,教师必须经常从学生中得到反馈信息,以便     

中华医用放射设备企业协会在沪成立

为了适应经济体制改革深入发展的需要,增强企业活力,加强企业之间的横向联系和相互交流,及时提供准确而有价值的经济信息和多方面的服务,经过近一年时间的筹备,中华医用放射设备企业协会于85年3月在上海正式成立。协会的宗旨是为企业服务。按照“自愿参加、自由退出”的原则,凡从事医用 X 线机、CT断层扫描装置、加速器、钴60治疗机等设备和医用电真空器件、铅玻璃等配套附件工业生产的企业和科研单位,不受部门、地区和所有制的限制均可参加。参加协会的,除国家医药局所属中国医疗器械工业公司归口管理的主要生产厂外,还有属电子工业部归口管理的杭州电子管厂等其他单位。原来杭州电子管厂和上海医疗器械九厂     

Evaluation of the Radiotherapy Treatment Planning in the Presence of a Magnetic Valve Tissue Expander

The combination of radiotherapy treatments and breast reconstruction, using temporary tissue expanders, generates several concerns due to the presence of a magnetic valve inside the radiation field. The objective of this work is to evaluate a radiotherapy treatment planning for a patient using a tissue expander. Isodose curve maps, obtained using radiochromic films, were compared to the ones calculated with two different dose calculation algorithms of the Eclipse radiotherapy Treatment Planning System (TPS), considering the presence or absence of the heterogeneity. The TPS calculation considering the presence of the heterogeneity shows changes around 5% in the isodose curves when they were compared with the calculation without heterogeneity correction. This calculation did not take in account the real density value of the heterogeneity. This limitation was quantified to be around 10% in comparison with the TPS calculation and experimental measurements using the radiochromic film. These results show that the magnetic valve should be taken in account in dose calculations of the TPS. With respect to the AAA and Pencil Beam Convolution algorithms, when the calculation is compared with the real distribution, AAA presents a distribution more similar to experimental dose distribution.     

Implementation of automatic plan optimization in Italy: Status and perspectives

PurposeTo investigate and report on the diffusion and clinical use of automated radiotherapy planning systems in Italy and to assess the perspectives of the community of Italian medical physicists involved in radiotherapy on the use of these tools.Materials and MethodsA survey of medical physicists (one per Institute) of 175 radiotherapy centers in Italy was conducted between February 21st and April 1st, 2021. The information collected included the institute’s characteristics, plan activity, availability/use of automatic tools and related issues regarding satisfaction, criticisms, expectations, and perceived professional modifications. Responses were analysed, including the impact of a few variables such as the institute type and experience.Results125 of the centers (71%) answered the survey, with regional variability (range: 47%–100%); among these, 49% have a TPS with some automatic option. Clinical use of automatic planning is present in 33% of the centers, with 13% applying it in >50% of their plans.Among the 125 responding centres the most used systems are Pinnacle (16%), Raystation (9%) and Eclipse (4%). The majority of participants consider the use of automated techniques to be beneficial, while only 1% do not see any advantage; 83% of respondents see the possibility of enriching their professional role as a potential benefit, while 3% see potential threats.ConclusionsOur survey shows that 49% of the responding centres have an automatic planning solution although clinically used in only 33% of the cases. Most physicists consider the use of automated techniques to be beneficial and show a prevalently positive attitude.     

Artifact-free CT images for electron beam therapy using a patient-specific non metallic shield

Patient’s CT images taken with metallic shields for radiotherapy suffer from artifacts. Furthermore, the treatment planning system (TPS) has a limitation on accurate dose calculations for high density materials. In this study, a Monte Carlo (MC)-based method was developed to accurately evaluate the dosimetric effect of the metallic shield. Two patients with a commercial tungsten shield of lens and two patients with a custom-made lead shield of lip were chosen to produce their non-metallic dummy shields using 3D scanner and printer. With these dummy shields, we generated artifact-free CT images. The maximum CT number allowed in TPS was assigned to metallic shields. MC simulations with real material information were carried out. In addition, clinically relevant dose-volumetric parameters were calculated for the comparison between MC and TPS. Relative dosimetry was performed using radiochromic films. The dose reductions below metallic structures were shown on MC dose distributions, but not evident on TPS dose distributions. The differences in dose-volumetric parameters of PTV between TPS and MC for eye shield cases were not clearly shown. However, the mean dose of lens from TPS and MC was different. The MC results were in superior agreement with measured data in relative dosimetry. The lens dose could be overestimated by TPS. The differences in dose-volumetric parameters of PTV between TPS and MC were generally larger in lip cases than in eye cases. The developed method is useful in predicting the realistic dose distributions around the organs blocked by the metallic shields.     

Comparison between two treatment planning systems for volumetric modulated arc therapy optimization for prostate cancer

PurposeTo investigate the performances of two commercial treatment planning systems (TPS) for Volumetric Modulated Arc Therapy (VMAT) optimization regarding prostate cancer. The TPS were compared in terms of dose distributions, treatment delivery parameters and quality control results.Materials and methodsFor ten patients, two VMAT plans were generated: one with Monaco TPS (Elekta) and one with Pinnacle TPS (Philips Medical Systems). The total prescribed dose was 78 Gy delivered in one 360° arc with a Synergy^® linear accelerator equipped with a MLCi2^®.ResultsVMAT with Monaco provided better homogeneity and conformity indexes but lower mean dose to PTVs than Pinnacle. For the bladder wall (p = 0.019), the femoral heads (p = 0.017), and healthy tissues (p = 0.005), significantly lower mean doses were found using Monaco. For the rectal wall, VMAT with Pinnacle provided a significantly (p = 0.047) lower mean dose, and lower dose into 50% of the volume (p = 0.047) compared to Monaco. Despite a greater number of monitor units (factor 1.5) for Monaco TPS, the total treatment time was equivalent to that of Pinnacle. The treatment delivery parameter analysis showed larger mean MLC area for Pinnacle and lower mean dose rate compared to Monaco. The quality control results gave a high passing rate (>97.4%) for the gamma index for both TPS but Monaco provided slightly better results.ConclusionFor prostate cancer patients, VMAT treatment plans obtained with Monaco and Pinnacle offered clinically acceptable dose distributions. Further investigations are in progress to confirm the performances of the two TPS for irradiating more complex volumes.     

Monte Carlo calculations of radiotherapy dose in “homogeneous” anatomy

Given the substantial literature on the use of Monte Carlo (MC) simulations to verify treatment planning system (TPS) calculations of radiotherapy dose in heterogeneous regions, such as head and neck and lung, this study investigated the potential value of running MC simulations of radiotherapy treatments of nominally homogeneous pelvic anatomy. A pre-existing in-house MC job submission and analysis system, built around BEAMnrc and DOSXYZnrc, was used to evaluate the dosimetric accuracy of a sample of 12 pelvic volumetric arc therapy (VMAT) treatments, planned using the Varian Eclipse TPS, where dose was calculated with both the Analytical Anisotropic Algorithm (AAA) and the Acuros (AXB) algorithm. In-house TADA (Treatment And Dose Assessor) software was used to evaluate treatment plan complexity, in terms of the small aperture score (SAS), modulation index (MI) and a novel exposed leaf score (ELS/ELA). Results showed that the TPS generally achieved closer agreement with the MC dose distribution when treatments were planned for smaller (single-organ) targets rather than larger targets that included nodes or metastases. Analysis of these MC results with reference to the complexity metrics indicated that while AXB was useful for reducing dosimetric uncertainties associated with density heterogeneity, the residual TPS dose calculation uncertainties resulted from treatment plan complexity and TPS model simplicity. The results of this study demonstrate the value of using MC methods to recalculate and check the dose calculations provided by commercial radiotherapy TPSs, even when the treated anatomy is assumed to be comparatively homogeneous, such as in the pelvic region.     

食管癌三维适形放疗和常规放疗比较

目的对比研究三维适形放疗（3DCRT）和常规模拟机定位放疗两种不同方法在食管癌放射治疗中的优缺点。方法 20例食管癌患者采用3DCRT方法进行治疗,应用同一治疗计划系统,制定适形放疗和常规模拟机定位放疗方案。结果与常规模拟定位机定位放疗相比,食管癌照射中3DCRT有最好的剂量分布,既可明显提高靶区的剂量,同时能较好地保护正常组织。结论食管癌的适形放疗技术能降低正常组织的放射损伤和并发症,提高放疗治疗的适形度,改善靶区的剂量分布。     

Assessment of out-of-field doses in radiotherapy treatments of paediatric patients using Monte Carlo methods and measurements

PurposeTo assess out-of-field doses in radiotherapy treatments of paediatric patients, using Monte Carlo methods to implement a new model of the linear accelerator validated against measurements and developing a voxelized anthropomorphic paediatric phantom.MethodsCT images of a physical anthropomorphic paediatric phantom were acquired and a dosimetric planning using a TPS was obtained. The CT images were used to perform the voxelization of the physical phantom using the ImageJ software and later implemented in MCNP. In order to validate the Monte Carlo model, dose measurements of the 6 MV beam and Linac with 120 MLC were made in a clinical setting, using ionization chambers and a water phantom. Afterwards TLD measurements in the physical anthropomorphic phantom were performed in order to assess the out-of-field doses in the eyes, thyroid, c-spine, heart and lungs.ResultsThe Monte Carlo model was validated for in-field and out-of-field doses with average relative differences below 3%. The average relative differences between TLD measurements and Monte Carlo is 14,3% whilst the average relative differences between TLD and TPS is 55,8%. Moreover, organs up to 22.5 cm from PTV center show TLD and MCNP6 relative differences and TLD and TPS relative differences up to 21.2% and 92.0%, respectively.ConclusionsOur study provides a novel model that could be used in clinical research, namely in dose evaluation outside the treatment fields. This is particularly relevant, especially in pediatric patients, for studying new radiotherapy treatment techniques, since it can be used to estimate the development of secondary tumours.     

Dosimetric Evaluation of Intensity-Modulated Radiotherapy,Volumetric Modulated Arc Therapy,and Helical Tomotherapy for Hippocampal-Avoidance Whole Brain Radiotherapy

Background

Whole brain radiotherapy (WBRT) is a vital tool in radiation oncology and beyond, but it can result in adverse health effects such as neurocognitive decline. Hippocampal Avoidance WBRT (HA-WBRT) is a strategy that aims to mitigate the neuro-cognitive side effects of whole brain radiotherapy treatment by sparing the hippocampi while delivering the prescribed dose to the rest of the brain. Several competing modalities capable of delivering HA-WBRT, include: Philips Pinnacle step-and-shoot intensity modulated radiotherapy (IMRT), Varian RapidArc volumetric modulated arc therapy (RapidArc), and helical TomoTherapy (TomoTherapy).

Methods

In this study we compared these methods using 10 patient datasets. Anonymized planning CT (computerized tomography) scans and contour data based on fused MRI images were collected. Three independent planners generated treatment plans for the patients using three modalities, respectively. All treatment plans met the RTOG 0933 criteria for HA-WBRT treatment.

Results

In dosimetric comparisons between the three modalities, TomoTherapy has a significantly superior homogeneity index of 0.15 ± 0.03 compared to the other two modalities (0.28 ± .04, p < .005 for IMRT and 0.22 ± 0.03, p < .005 for RapidArc). RapidArc has the fastest average delivery time of 2.5 min compared to the other modalities (15 min for IMRT and 18 min for TomoTherapy).

Conclusion

TomoTherapy is considered to be the preferred modality for HA-WBRT due to its superior dose distribution. When TomoTherapy is not available or treatment time is a concern, RapidArc can provide sufficient dose distribution meeting RTOG criteria and efficient treatment delivery.     

A comparison of electronic portal dosimetry verification methods for use in stereotactic radiotherapy

Three methods of transit dosimetry using Electronic Portal Imaging Devices (EPIDs) were investigated for use in routine in-vivo dosimetry for cranial stereotactic radiosurgery and radiotherapy. The approaches examined were (a) A full Monte Carlo (MC) simulation of radiation transport through the linear accelerator and patient; (b) Calculation of the expected fluence by a treatment planning system (TPS); (c) Point doses calculated along the central axis compared to doses calculated using parameters acquired using the EPID. A dosimetric comparison of each of the three methods predicted doses at the imager plane to within ±5% and a gamma comparison for the MC and TPS based approaches showed good agreement for a range of dose and distance to agreement criteria. The MC technique was most time consuming, followed by the TPS calculation with the point dose calculation significantly quicker than the other methods.     

Virtual patient 3D dose reconstruction using in air EPID measurements and a back-projection algorithm for IMRT and VMAT treatments

PurposeAt our institute, a transit back-projection algorithm is used clinically to reconstruct in vivo patient and in phantom 3D dose distributions using EPID measurements behind a patient or a polystyrene slab phantom, respectively. In this study, an extension to this algorithm is presented whereby in air EPID measurements are used in combination with CT data to reconstruct ‘virtual’ 3D dose distributions. By combining virtual and in vivo patient verification data for the same treatment, patient-related errors can be separated from machine, planning and model errors.Methods and materialsThe virtual back-projection algorithm is described and verified against the transit algorithm with measurements made behind a slab phantom, against dose measurements made with an ionization chamber and with the OCTAVIUS 4D system, as well as against TPS patient data. Virtual and in vivo patient dose verification results are also compared.ResultsVirtual dose reconstructions agree within 1% with ionization chamber measurements. The average γ-pass rate values (3% global dose/3 mm) in the 3D dose comparison with the OCTAVIUS 4D system and the TPS patient data are 98.5 ± 1.9%(1SD) and 97.1 ± 2.9%(1SD), respectively. For virtual patient dose reconstructions, the differences with the TPS in median dose to the PTV remain within 4%.ConclusionsVirtual patient dose reconstruction makes pre-treatment verification based on deviations of DVH parameters feasible and eliminates the need for phantom positioning and re-planning. Virtual patient dose reconstructions have additional value in the inspection of in vivo deviations, particularly in situations where CBCT data is not available (or not conclusive).