Computational Dosimetry and Treatment Planning Considerations for Neutron Capture Therapy

Specialized treatment planning software systems are generally required for neutron capture therapy (NCT) research and clinical applications. The standard simplifying approximations that work well for treatment planning computations in the case of many other modalities are usually not appropriate for application to neutron transport. One generally must obtain an explicit three-dimensional numerical solution of the governing transport equation, with energy-dependent neutron scattering completely taken into account. Treatment planning systems that have been successfully introduced for NCT applications over the past 15 years rely on the Monte Carlo stochastic simulation method for the necessary computations, primarily because of the geometric complexity of human anatomy. However, historically, there has also been interest in the application of deterministic methods, and there have been some practical developments in this area. Most recently, interest has turned toward the creation of treatment planning software that is not limited to any specific therapy modality, with NCT as only one of several applications. A key issue with NCT treatment planning has to do with boron quantification, and whether improved information concerning the spatial biodistribution of boron can be effectively used to improve the treatment planning process. Validation and benchmarking of computations for NCT are also of current developmental interest. Various institutions have their own procedures, but standard validation models are not yet in wide use.     

Evaluation of an Electronic Portal Imaging Device for Transit Dosimetry

The possibility of using a commercially available electronic portal imaging device for transit dosimetry was investigated. The detection unit of the device comprises a metal plate/fluorescence screen and a camera. Basic parameters of this system were investigated: stability, detector uniformity, dose-response curve, field-size dependence and phantom-thickness dependence. It was found that in terms of relative dosimetry, portal images corrected for detector non-uniformity are in good agreement (within 5%) with transit dose distributions measured by film dosimetry. For dose determination, it was found that the use of the device is hampered by an important field-size dependence and phantom-thickness dependence. Both correction factors should be applied if the device is to be used for this purpose.     

Scientific Developments in Imaging and Dosimetry for Molecular Radiotherapy

Molecular radiotherapy is a rapidly developing field with new vector and isotope combinations continually added to market. As with any radiotherapy treatment, it is vital that the absorbed dose and toxicity profile are adequately characterised. Methodologies for absorbed dose calculations for radiopharmaceuticals were generally developed to characterise stochastic effects and not suited to calculations on a patient-specific basis. There has been substantial scientific and technological development within the field of molecular radiotherapy dosimetry to answer this challenge. The development of imaging systems and advanced processing techniques enable the acquisition of accurate measurements of radioactivity within the body. Activity assessment combined with dosimetric models and radiation transport algorithms make individualised absorbed dose calculations not only feasible, but commonplace in a variety of commercially available software packages. The development of dosimetric parameters beyond the absorbed dose has also allowed the possibility to characterise the effect of irradiation by including biological parameters that account for radiation absorbed dose rates, gradients and spatial and temporal energy distribution heterogeneities. Molecular radiotherapy is in an exciting time of its development and the application of dosimetry in this field can only have a positive influence on its continued progression.     

CT扫描/重建参数对三维治疗计划系统影像的影响

[目的]研究CT模拟定位中,CT扫描/重建参数对三维治疗计划重建的三维假体的几何精确度的影响.[方法]在西门子CT模拟机（Somatom plus 4）上扫描自制模体,扫描所得图像登记到ADAC三维治疗计划系统重建成三维假体,测量假体的相关坐标数据并与模体的实际数据相比较;对Catphan 412模体扫描并测量各组图像的实际层厚,讨论实际层厚的变化对计划系统中登记影像的几何精度影响.[结果]（1）CT扫描所采用的不同扫描/重建参数对三维计划系统中重建的三维假体的左右及上下方向的几何精度影响不大,但对重建假体的前后方向（即模体扫描的步进方向）的几何精度有一定的影响.（2）CT扫描所采用的螺距及重建模式会对层厚敏感度曲线（SSP）半高宽值产生影响,该变化对重建假体的前后方向几何精度同样有一定的影响.[结论]重建CT图像的前后方向的几何误差是随着扫描层厚增加而增加,主要是由于CT扫描的部分容积效应影响.单纯增加螺距或使用360度线性内插（Wide）重建模式,都会引起CT图像实际层厚的增加,引起更大的容积效应影响.同时部分容积效应也会导致三维治疗计划系统中数字重建影像（DRR）分辨率的降低.     

Cost Minimisation Analysis: Kilovoltage Imaging with Automated Repositioning Versus Electronic Portal Imaging in Image-guided Radiotherapy for Prostate Cancer

AimsTo compare the treatment time and cost of prostate cancer fiducial marker image-guided radiotherapy (IGRT) using orthogonal kilovoltage imaging (KVI) and automated couch shifts and orthogonal electronic portal imaging (EPI) and manual couch shifts.Materials and methodsIGRT treatment delivery times were recorded automatically on either unit. Costing was calculated from real costs derived from the implementation of a new radiotherapy centre. To derive cost per minute for EPI and KVI units the total annual setting up and running costs were divided by the total annual working time. The cost per IGRT fraction was calculated by multiplying the cost per minute by the duration of treatment. A sensitivity analysis was conducted to test the robustness of our analysis. Treatment times without couch shift were compared.ResultsTime data were analysed for 8648 fractions, 6057 from KVI treatment and 2591 from EPI treatment from a total of 294 patients. The median time for KVI treatment was 6.0 min (interquartile range 5.1–7.4 min) and for EPI treatment it was 10.0 min (interquartile range 8.3–11.8 min) (P value < 0.0001). The cost per fraction for KVI was A$258.79 and for EPI was A$345.50. The cost saving per fraction for KVI varied between A$66.09 and A$101.64 by sensitivity analysis. In patients where no couch shift was made, the median treatment delivery time for EPI was 8.8 min and for KVI was 5.1 min.ConclusionsTreatment time is less on KVI units compared with EPI units. This is probably due to automation of couch shift and faster evaluation of imaging on KVI units. Annual running costs greatly outweigh initial setting up costs and therefore the cost per fraction was less with KVI, despite higher initial costs. The selection of appropriate IGRT equipment can make IGRT practical within radiotherapy departments.     

Technical Report: Development and Implementation of an Open Source Template Interpretation Class Library for Automated Treatment Planning

PurposeWidespread implementation of automated treatment planning in radiation therapy remains elusive owing to variability in clinic and physician preferences, making it difficult to ensure consistent plan parameters. We have developed an open-source class library with the aim to improve efficiency and consistency for automated treatment planning in radiation therapy.Methods and MaterialsAn open-source class library has been developed that interprets clinical templates within a commercial treatment planning system into a treatment plan for automated planning. This code was leveraged for the automated planning of 39 patients and retrospectively compared with the 78 clinically approved manual plans.ResultsFrom the initial 39 patients, 74 of 78 plans were successfully generated without manual intervention. The target dose was more homogeneous for automated plans, with an average homogeneity index of 3.30 for manual plans versus 3.11 for automated plans (P = .107). The generalized equivalent uniform dose (gEUD) was decreased in the femurs and rectum for automated plans, with a mean gEUD of 3746 cGy versus 3338 cGy (P ≤ 0.001) and 5761 cGy versus 5634 cGy (P ≤ 0.001) for the femurs and rectum, respectively. Dose metrics for the bladder and rectum (V6500 cGy and V4000 cGy) showed recognizable but insignificant improvements. All automated plans delivered for quality assurance passed a gamma analysis (>95%), with an average composite pass rate of 99.3% for pelvis plans and 98.8% for prostate plans. Deliverability parameters such as total monitor units and aperture complexity indicated deliverable plans.ConclusionsProstate cancer and pelvic node radiation therapy can be automated using volumetric modulated arc therapy planning and clinical templates based on a standardized clinical workflow. The class library developed in this study conveniently interfaced between the plan template and the treatment planning system to automatically generate high-quality plans on customizable templates.     

三维治疗计划系统和CT模拟定位工作站影像重建质量检测

[目的]利用影像质控体模，测量三种型号的TPS／CT—Sim工作站在不同CT扫描参数时图像重建的几何结构和射野设置的精度，以及CT值的改变范围。[方法]质控体模内置15种不同形状、大小和密度的模块，体积大小范同为0．5cc～125．0cc，相对电子密度为0．190～1．512，在CT模拟机扫描后输入到各TPS／CT—Sim工作站进行影像重建测试。测试条件分为6组不同的扫描参数。比较各系统在不同扫描条件下的影像重建质量、计划设计的几何精度及CT值与相对电子密度的改变。[结果]不同仰S／CT-Sim工作站的影像重建均存在不同程度的偏差（-27％～27．4％）：CT扫描参数对各系统的影像重建体积有明显的影响，扫描层厚和螺距对重建体积的影响较其他因素显著；层厚扫描为3mm及扫描螺距为1．0时，各系统图像重建体积误差较小；CT扫描电压和电流对图像重建体积的影响不明显但会使CT值产生明显差异。[结论]各放疗单位有必要对临床使用的每台TPS／CT-Sim和CT扫描参数进行影像质量检测和评估，以决定适合具体系统的使用条件和误差范围；在使用体积剂量工具进行治疗计划评估时应考虑影像重建体积的误差。     

三维治疗计划系统和GT模拟定位工作站影像重建质量检测

[目的]利用影像质控体模,测量三种型号的TPS/CT-Sim工作站在不同CT扫描参数时图像重建的几何结构和射野设置的精度,以及CT值的改变范围.[方法]质控体模内置15种不同形状、大小和密度的模块,体积大小范围为0.5cc～125.0cc,相对电子密度为0.190～1.512,在CT模拟机扫描后输入到各TPS/CT-Sim工作站进行影像重建测试.测试条件分为6组不同的扫描参数.比较各系统在不同扫描条件下的影像重建质量、计划设计的几何精度及CT值与相对电子密度的改变.[结果]不同TPS/CT-Sim工作站的影像重建均存在不同程度的偏差(-27%～27.4%);CT扫描参数对各系统的影像重建体积有明显的影响,扫描层厚和螺距对重建体积的影响较其他因素显著;层厚扫描为3mm及扫描螺距为1.0时,各系统图像重建体积误差较小;CT扫描电压和电流对图像重建体积的影响不明显但会使CT值产生明显差异.[结论]各放疗单位有必要对临床使用的每台TPS/CT-Sim和CT扫描参数进行影像质量检测和评估,以决定适合具体系统的使用条件和误差范围:在使用体积剂量工具进行治疗计划评估时应考虑影像重建体积的误差.     

Multicentre Trials on Standardised Quantitative Imaging and Dosimetry for Radionuclide Therapies

The aim of this review is to summarise the efforts undertaken so far to compare or standardise quantitative imaging with gamma cameras across centres for multicentre trials in radionuclide therapies. Overall, 10 studies were identified, five of which were set up as a multicentre effort for standardising and comparing methods for quantitative imaging. One study used positron emission tomography imaging with ¹²⁴I. In the remaining studies, measurements were carried out with planar imaging, single photon emission computed tomography/computed tomography (SPECT/CT) or a combination of both. Three studies used radioactive calibration sources that were traceable to national standards. Most of the studies were set up in the framework of multicentre clinical trials in an effort to obtain comparable quantification across sites. The use of state-of-the-art SPECT/CT systems and reconstructions has emerged as the method of choice for dosimetry in clinical trials for radionuclide therapies.     

直肠癌根治性放疗合成计划设计的

[目的]比较适形与调强基础上合成叠加调强计划的剂量学差异.[方法]选取根治性放疗直肠癌靶区,第一程计划分别用3野适形、4野适形和5野调强对PTV给予50Gy,在第一程计划基础上合成调强计划(IMRT)给予PGTV到66Gy根治剂量.危及器官都不超量的情况下比较靶区等效生物剂量.[结果]3个叠加后计划无明显差异.不考虑第一程计划,第二程计划差异明显,PGTV 95％剂量:5野剂量为15Gy,4野剂量为13.18Gy,3野剂量为8.82Gy.[结论]直肠癌根治性放疗局部加量调强基础上的合成计划等效生物剂量更接近预期值.     

乳腺癌改良根治术后胸壁切线野计划和电子线计划的剂量学比较

目的:比较乳腺癌改良根治术后胸壁X线切线野放疗计划和电子线单野放疗计划肿瘤靶区与正常组织的剂量学分布差异,探讨最合适的照射方式.方法:选取2007年8月～2008年6月收治的30例有胸壁照射适应证的乳腺癌改良根治术后患者.进行CT模拟定位,利用三维治疗计划系统为每例患者设计两种不同的胸壁放射治疗计划:X线切线野计划和电子线单野计划,胸壁处方剂量均为50Gy/25次,用剂量体积直方图(DVH)来比较两种计划中临床靶区(CTV)和心脏、同侧肺的剂量学差异.结果:左侧胸壁切线野计划和电子线野计划肿瘤靶区的最大剂量(Dmax)分别为5306±17cGy、5536±301cGy(P=0.02);右侧胸壁Dmax分别为5228±136cGy,5554±253cGy(P=0.01),统计学有显著性差异.两种计划肿瘤靶区其余指标(Dmean、D90和V105%、V110%以及不均匀指数HI)均无统计学差异.左侧胸壁切线野计划和电子线野计划同侧肺平均剂量分别为1095±243cGy和1723±624(P=-0.001),肺V20分别为21±5%和36±13%(P=0.001),两者均有显著性差异.其余指标(心脏的平均剂量、V30)无统计学差异.右侧胸壁两种计划所有正常组织指标均无统计学差异.结论:乳腺癌改良根治术后胸壁x线切线野放疗比电子线单野放疗有一定的剂量优势,可以减少胸壁的最高剂量,左侧胸壁能减少同侧肺受照射的体积和剂量,更好地保护正常组织.     

原发性中枢神经系统淋巴瘤的影像学特点及治疗

原发性中枢神经系统淋巴瘤是一种比较罕见的结外原发非霍奇金淋巴瘤（NHL）,其细胞来源多为弥漫大B淋巴细胞,淋巴细胞影像学表现为单发或多发的深部脑实质、脑室周围或脑膜等处的病变。其治疗尚无标准方案,目前多采用放化疗结合的综合治疗。化疗采用以大剂量MTX为主的方案,全脑放疗已被公认为治疗PCNSL的有效手段。但最佳的化疗方案组合、MTX最佳剂量及放疗剂量仍无定论。我们收治一例原发性中枢神经系统淋巴瘤,于外院行肿瘤切除术,术后予阿糖胞苷加大剂量MTX化疗6程后残留,现经多学科讨论后认为应予辅助放疗加替莫唑胺维持化疗。现患者已完成放疗,替莫唑胺维持化疗中。本文就此病例的影像特点及治疗进行讨论。