Physics and Imaging in Radiation Oncology最新文献_第5页

Results of 2023 survey on the use of synthetic computed tomography for magnetic resonance Imaging-only radiotherapy: Current status and future steps 2023 年关于使用合成计算机断层扫描进行纯磁共振成像放射治疗的调查结果：现状和未来步骤

IF 3.4 Q2 ONCOLOGY

Physics and Imaging in Radiation Oncology

Pub Date : 2024-10-01 DOI: 10.1016/j.phro.2024.100652

M. Fusella , E. Alvarez Andres , F. Villegas , L. Milan , TM. Janssen , R. Dal Bello , C. Garibaldi , L. Placidi , D. Cusumano

Background and purpose

The emergence of synthetic CT (sCT) in MR-guided radiotherapy (MRgRT) represents a significant advancement, supporting MR-only workflows and online treatment adaptation. However, the lack of consensus guidelines has led to varied practices. This study reports results from a 2023 ESTRO survey aimed at defining current practices in sCT development and use.

Materials and methods

An survey was distributed to ESTRO members, including 98 questions across four sections on sCT algorithm generation and usage. By June 2023, 100 centers participated. The survey revealed diverse clinical experiences and roles, with primary sCT use in the pelvis (60%), brain (15%), abdomen (11%), thorax (8%), and head-and-neck (6%). sCT was mostly used for conventional fractionation treatments (68%), photon SBRT (40%), and palliative cases (28%), with limited use in proton therapy (4%).

Results

Conditional GANs and GANs were the most used neural network architectures, operating mainly on 1.5 T and 3 T MRI images. Less than half used paired images for training, and only 20% performed image selection. Key MR image quality parameters included magnetic field homogeneity and spatial integrity. Half of the respondents lacked a dedicated sCT-QA program, and many did not apply sanitychecks before calculation. Selection strategies included age, weight, and metal artifacts. A strong consensus (95%) emerged for vendor neutral guidelines.

Conclusion

The survey highlights the need for expert-based, vendor-neutral guidelines to standardize sCT tools, metrics, and clinical protocols, ensuring effective sCT use in MR-guided radiotherapy.

背景和目的合成 CT（sCT）在磁共振引导放射治疗（MRgRT）中的出现代表了一项重大进步，它支持只用磁共振的工作流程和在线治疗适应性。然而，由于缺乏一致的指导原则，导致实践方法各不相同。本研究报告了 2023 年 ESTRO 调查的结果，该调查旨在确定 sCT 开发和使用的当前实践。材料和方法向 ESTRO 成员分发了一份调查表，其中包括有关 sCT 算法生成和使用的四个部分的 98 个问题。截至 2023 年 6 月，共有 100 个中心参与了调查。调查显示了不同的临床经验和作用，sCT主要用于骨盆（60%）、脑部（15%）、腹部（11%）、胸部（8%）和头颈部（6%）。sCT 主要用于常规分层治疗（68%）、光子 SBRT（40%）和姑息性病例（28%），质子治疗的使用有限（4%）。不到一半的神经网络使用成对图像进行训练，只有 20% 的神经网络进行了图像选择。关键的磁共振图像质量参数包括磁场均匀性和空间完整性。半数受访者没有专门的 sCT-QA 程序，许多人在计算前没有进行卫生检查。选择策略包括年龄、体重和金属伪影。该调查突出表明，有必要制定以专家为基础、供应商中立的指南，以规范 sCT 工具、指标和临床方案，确保在 MR 引导放射治疗中有效使用 sCT。

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引用次数: 0

Integrated framework for quantitative T2-weighted MRI analysis following prostate cancer radiotherapy 前列腺癌放疗后 T2 加权磁共振成像定量分析综合框架

IF 3.4 Q2 ONCOLOGY

Physics and Imaging in Radiation Oncology

Pub Date : 2024-10-01 DOI: 10.1016/j.phro.2024.100660

Evangelia I. Zacharaki , Adrian L. Breto , Ahmad Algohary , Veronica Wallaengen , Sandra M. Gaston , Sanoj Punnen , Patricia Castillo , Pradip M. Pattany , Oleksandr N. Kryvenko , Benjamin Spieler , John C. Ford , Matthew C. Abramowitz , Alan Dal Pra , Alan Pollack , Radka Stoyanova

Purpose

The aim of this study is to develop a framework for quantitative analysis of longitudinal T2-weighted MRIs (T2w) following radiotherapy (RT) for prostate cancer.

Materials and methods

The developed methodology includes: (i) deformable image registration of longitudinal series to pre-RT T2w for automated detection of prostate, peripheral zone (PZ), and gross tumor volume (GTV); and (ii) T2w signal-intensity harmonization based on three reference tissues. The REgistration and HARMonization (REHARM) framework was applied on T2w acquired in a clinical trial consisting of two pre-RT and three post-RT MRI exams. Image registration was assessed by the DICE coefficient between automatic and manual contours, and intensity normalization via inter-patient histogram intersection. Longitudinal consistency was evaluated by the repeatability coefficient and Pearson correlation (r) between the two T2w exams before RT.

Results

T2w from 107 MRI exams (23 patients) were utilized. Following REHARM, the histogram intersections for prostate, PZ and GTV increased from median = 0.43/0.16/0.13 to 0.66/0.44/0.46. The repeatability in T2w intensity estimation was better for the automatic than the manual contours for all three regions of interest (r = 0.9, p < 0.0001, for GTV). The changes in the tissues’ T2w values pre- and post-RT became significant, indicating the measurable quantitative signal related to radiation.

Conclusions

The developed methodology allows to automate longitudinal analysis reducing data acquisition-related variation and improving consistency. The quantitative characterization of RT-induced changes in T2w will lead to new understanding of radiation effects enabling prediction modeling of RT response.

目的本研究旨在开发一种框架，用于对前列腺癌放疗（RT）后的纵向 T2 加权磁共振成像（T2w）进行定量分析：开发的方法包括：(i) 将纵向系列图像与 RT 前的 T2w 进行可变形图像配准，以自动检测前列腺、外周区 (PZ) 和肿瘤总体积 (GTV)；(ii) 基于三个参考组织的 T2w 信号强度协调。REgistration and HARMonization (REHARM) 框架应用于一项临床试验中获取的 T2w 图像，该试验包括两次前列腺癌术前和三次前列腺癌术后 MRI 检查。通过自动轮廓和手动轮廓之间的 DICE 系数评估图像配准，并通过患者间直方图交集评估强度归一化。通过 RT 前两次 T2w 检查之间的重复性系数和皮尔逊相关性（r）来评估纵向一致性。REHARM后，前列腺、PZ和GTV的直方图交点从中位数=0.43/0.16/0.13增加到0.66/0.44/0.46。在所有三个感兴趣区中，自动轮廓图的 T2w 强度估计重复性均优于手动轮廓图（对于 GTV，r = 0.9，p < 0.0001）。RT前后组织 T2w 值的变化显著，表明与辐射有关的定量信号是可测量的。对 RT 引起的 T2w 变化进行定量分析将有助于对辐射效应有新的认识，从而建立 RT 反应的预测模型。

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引用次数: 0

Dwell time shaping in inverse treatment planning for cervical brachytherapy 宫颈近距离放射治疗反向治疗规划中的停留时间整形

IF 3.4 Q2 ONCOLOGY

Physics and Imaging in Radiation Oncology

Pub Date : 2024-10-01 DOI: 10.1016/j.phro.2024.100672

Frida Dohlmar , Björn Morén , Michael Sandborg , Torbjörn Larsson , Åsa Carlsson Tedgren

Background and purpose

Manual treatment planning for cervical brachytherapy is a challenging task; therefore, we investigated a method for inverse treatment planning using pseudo-structures to control the dwell distribution. Our hypothesis was that this method could produce treatment plans with a pear-shaped dose distribution and a high central dose, that comply with clinical constraints.

Materials and methods

Data from 16 previously treated patients were used to compare three treatment planning methods: i) manual, ii) straightforward inverse, and iii) inverse with pseudo-structures. The treatment plans were compared using dose-volume histogram parameters and by analysing the dwell times, and the distribution of total reference air-kerma (TRAK) in the different parts of the applicator. Methods were evaluated in one treatment planning system and verified in a second treatment planning system.

Results

The median dose to 90 % of the clinical tumor volume was 7.6 Gy, 7.8 Gy and 8.1 Gy for manual, pseudo-structure and straightforward methods respectively. Distribution of TRAK for the different parts of the applicator for the three methods (manual, pseudo-structures, and straightforward), with combined intracavitary and interstitial treatments, were for vaginal part 39 %, 33 % and 15 %, for intra-uterine part 47 %, 50 % and 47 % and for interstitial part 13 %, 17 % and 38 % respectively. The results were similar in the second treatment planning system.

Conclusion

The developed pseudo-structures worked as intended in shaping the dwell time distribution and in meeting the clinical constraints for both investigated treatment planning systems.

背景和目的宫颈近距离放射治疗的手动治疗计划是一项具有挑战性的任务；因此，我们研究了一种使用伪结构控制驻留分布的反向治疗计划方法。我们的假设是，这种方法可以产生梨形剂量分布和高中心剂量的治疗计划，并符合临床限制条件。材料和方法使用 16 名先前接受过治疗的患者的数据，比较三种治疗计划方法：i) 手动；ii) 直接反向；iii) 使用伪结构的反向。使用剂量-体积直方图参数，并通过分析停留时间和涂抹器不同部位的总参考空气热玛（TRAK）分布，对治疗计划进行比较。结果90%临床肿瘤体积的中位剂量分别为7.6 Gy、7.8 Gy和8.1 Gy。在三种方法（手动、伪结构和直接）中，结合腔内和间质治疗的不同部位的 TRAK 分布情况分别为：阴道部位 39%、33% 和 15%，宫腔内部位 47%、50% 和 47%，间质部位 13%、17% 和 38%。在第二种治疗计划系统中，结果与此类似。

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引用次数: 0

3D gel dosimeter assessment for end-to-end geometric accuracy determination of the online adaptive workflow on the 1.5 T MR-linac 用于确定 1.5 T 磁共振成像仪在线自适应工作流程端到端几何精度的三维凝胶剂量计评估

IF 3.4 Q2 ONCOLOGY

Physics and Imaging in Radiation Oncology

Pub Date : 2024-10-01 DOI: 10.1016/j.phro.2024.100664

Stijn Oolbekkink, Jochem W.H. Wolthaus, Bram van Asselen, Bas W. Raaymakers

Background and purpose:

During an end-to-end (E2E) test on the online workflow of the MR-linac, the performance of the treatment starting from the acquisition of pre-treatment MRI scans and ending with dose delivery is quantified. In such a test, the geometrical accuracy of the entire workflow is assessed. Ideally, the 3D geometrical accuracy of dose delivery on an MR-linac should be assessed using dosimeters that provide 3D dose distributions. Gel dosimeters, for instance, have proven to be valuable tools for evaluating 3D dose distributions on an MR-linac. In this study, we investigated the use of 3D gel dosimeters for the assessment of the 3D geometrical accuracy and reproducibility of the adaptive procedure on an MR-linac in an E2E verification.

Materials and methods:

All measurements were performed on a clinical Unity MR-linac using 3D gel dosimeters in an anthropomorphic head phantom. Film measurements were performed as a reference dosimeter. An online adapt-to-shape procedure was performed for each measurement.

Results:

The geometric accuracy and reproducibility of the gel dosimeter measurements were high, and similar to all in-plane film measurements. The largest shift found was 0.3 mm for the gel dosimeter, and 0.6 mm for the in-plane film measurements. The 3D displacement vectors of the gel dosimeter showed similar uncertainties as the in-plane film 2D displacement vectors.

Conclusions:

Gel dosimeters can be used for the assessment of the 3D end-to-end geometric accuracy of an MR-linac.

背景和目的：在对核磁共振成像仪的在线工作流程进行端到端（E2E）测试时，要量化从获取治疗前核磁共振成像扫描开始到剂量投放结束的治疗性能。在这种测试中，要对整个工作流程的几何精度进行评估。理想情况下，应使用可提供三维剂量分布的剂量计来评估磁共振成像仪上剂量投放的三维几何精度。例如，凝胶剂量计已被证明是评估磁共振成像仪三维剂量分布的重要工具。在这项研究中，我们研究了在 E2E 验证中使用三维凝胶剂量计评估磁共振成像仪上自适应程序的三维几何精度和可重复性。胶片测量是作为参考剂量计进行的。结果：凝胶剂量计测量的几何精度和再现性都很高，与所有平面内胶片测量结果相似。凝胶剂量计的最大位移为 0.3 毫米，平面薄膜测量的最大位移为 0.6 毫米。凝胶剂量计的三维位移矢量显示出与平面薄膜二维位移矢量相似的不确定性。

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引用次数: 0

A deep learning model for predicting the modified micro-dosimetric kinetic model-based dose and the dose-averaged linear energy transfer for prostate cancer in carbon ion therapy 用于预测碳离子疗法中前列腺癌的改良微剂量动力学模型剂量和剂量平均线性能量转移的深度学习模型

IF 3.4 Q2 ONCOLOGY

Physics and Imaging in Radiation Oncology

Pub Date : 2024-10-01 DOI: 10.1016/j.phro.2024.100671

Liwen Zhang , Weiwei Wang , Ping Li , Qing Zhang , Rongcheng Han

Adaptive carbon ion radiotherapy for localized prostate cancer requires accurate evaluation of biological dose and dose-averaged linear energy transfer (LET_d) changes. This study developed a deep learning model to rapidly predict the modified micro-dosimetric kinetic model (mMKM)-based dose and LET_d distributions. Using data from fifty patients for training and testing, the model achieved gamma passing rates exceeding 96% compared to true mMKM-based dose and LET_d recalculated from local effect model I (LEM I) plans. Incorporating computed tomography images, contours, physical dose, and LEM I-based dose as inputs, this model provided a rapid, accurate tool for comprehensive evaluations.

针对局部前列腺癌的自适应碳离子放疗需要准确评估生物剂量和剂量平均线性能量传递（LETd）的变化。本研究开发了一种深度学习模型，用于快速预测基于修正微剂量动力学模型（mMKM）的剂量和线性能量传递分布。利用 50 名患者的数据进行训练和测试，与根据局部效应模型 I（LEM I）计划重新计算的基于 mMKM 的真实剂量和 LETd 相比，该模型的伽马通过率超过 96%。该模型将计算机断层扫描图像、等值线、物理剂量和基于 LEM I 的剂量作为输入，为综合评估提供了快速、准确的工具。

引用次数: 0

Treatment planning for very high energy electrons: Studies that indicate the potential of the modality 高能电子治疗规划：显示该模式潜力的研究

IF 3.4 Q2 ONCOLOGY

Physics and Imaging in Radiation Oncology

Pub Date : 2024-10-01 DOI: 10.1016/j.phro.2024.100670

James L. Bedford, Uwe Oelfke

Background and purpose

Radiotherapy using Very High Energy Electrons (VHEE) has the potential to reduce dose to organs at risk compared to photons. This article therefore reviews treatment planning for VHEE, to clarify the potential benefit of the modality.

Materials and methods

Articles on VHEE were identified and those which focused on treatment planning were manually selected, particularly those which contained results on patient datasets. Benefits in absorbed dose to organs at risk were converted to percentages of prescription dose so as to provide uniform, clinically relevant reporting.

Results

Increased beam energy was found to reduce electron scatter and give rise to a narrower penumbra but lead to a rather constant depth dose curve, which was not as useful for sparing normal tissues as that of protons. The sharp penumbra of VHEE was of benefit in treatment planning for producing treatment plans with conformal dose shaping, with improved dose to critical structures being demonstrated for several treatment sites. Mean dose to critical structures, relative to the prescribed dose, was in the order of 0–10% lower than photons and 0–10% higher than protons. The delivery technology and dose distributions were also promising for radiotherapy with ultra-high dose rate (FLASH).

Conclusion

At present, the potential clinical benefit of VHEE relative to photons or protons is small. Further studies are needed to more precisely quantify the relative performance of broad beams versus pencil beam scanning and to investigate treatment sites that might benefit maximally from the use of VHEE beams.

背景和目的与光子相比，使用甚高能电子（VHEE）进行放疗有可能减少危险器官的剂量。因此，本文对 VHEE 的治疗计划进行了回顾，以明确该模式的潜在益处。材料与方法对有关 VHEE 的文章进行了识别，并人工筛选出那些关注治疗计划的文章，尤其是那些包含患者数据集结果的文章。结果发现增加射束能量可减少电子散射，使半影更窄，但导致深度剂量曲线相当恒定，不像质子那样有助于保护正常组织。超高频电子显微镜的尖锐半影有利于治疗计划的制定，从而产生适形剂量整形的治疗计划，多个治疗部位的关键结构的剂量都得到了改善。与规定剂量相比，关键结构的平均剂量比光子低 0-10%，比质子高 0-10%。结论目前，相对于光子或质子，VHEE 的潜在临床效益还很小。还需要进一步研究，以更精确地量化宽光束与铅笔束扫描的相对性能，并调查可能从使用 VHEE 光束中获益最大的治疗部位。

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引用次数: 0

Automatic segmentation for magnetic resonance imaging guided individual elective lymph node irradiation in head and neck cancer patients 磁共振成像引导头颈部癌症患者进行个体选择性淋巴结照射的自动分割技术

IF 3.4 Q2 ONCOLOGY

Physics and Imaging in Radiation Oncology

Pub Date : 2024-10-01 DOI: 10.1016/j.phro.2024.100655

Floris C.J. Reinders , Mark H.F. Savenije , Mischa de Ridder , Matteo Maspero , Patricia A.H. Doornaert , Chris H.J. Terhaard , Cornelis P.J. Raaijmakers , Kaveh Zakeri , Nancy Y. Lee , Eric Aliotta , Aneesh Rangnekar , Harini Veeraraghavan , Marielle E.P. Philippens

Background and purpose

In head and neck squamous cell carcinoma (HNSCC) patients, the radiation dose to nearby organs at risk can be reduced by restricting elective neck irradiation from lymph node levels to individual lymph nodes. However, manual delineation of every individual lymph node is time-consuming and error prone. Therefore, automatic magnetic resonance imaging (MRI) segmentation of individual lymph nodes was developed and tested using a convolutional neural network (CNN).

Materials and methods

In 50 HNSCC patients (UMC-Utrecht), individual lymph nodes located in lymph node levels Ib-II-III-IV-V were manually segmented on MRI by consensus of two experts, obtaining ground truth segmentations. A 3D CNN (nnU-Net) was trained on 40 patients and tested on 10. Evaluation metrics were Dice Similarity Coefficient (DSC), recall, precision, and F1-score. The segmentations of the CNN was compared to segmentations of two observers. Transfer learning was used with 20 additional patients to re-train and test the CNN in another medical center.

Results

nnU-Net produced automatic segmentations of elective lymph nodes with median DSC: 0.72, recall: 0.76, precision: 0.78, and F1-score: 0.78. The CNN had higher recall compared to both observers (p = 0.002). No difference in evaluation scores of the networks in both medical centers was found after re-training with 5 or 10 patients.

Conclusion

nnU-Net was able to automatically segment individual lymph nodes on MRI. The detection rate of lymph nodes using nnU-Net was higher than manual segmentations. Re-training nnU-Net was required to successfully transfer the network to the other medical center.

背景和目的在头颈部鳞状细胞癌（HNSCC）患者中，通过将选择性颈部照射从淋巴结水平限制到单个淋巴结，可以减少对附近危险器官的辐射剂量。然而，人工划定每个淋巴结既费时又容易出错。因此，我们使用卷积神经网络（CNN）开发并测试了单个淋巴结的自动磁共振成像（MRI）分割。材料与方法在 50 名 HNSCC 患者（UMC-Utrecht）中，通过两名专家的共识，对位于淋巴结 Ib-II-III-IV-V 层的单个淋巴结进行了 MRI 人工分割，获得了基本真实分割结果。在 40 名患者身上训练了 3D CNN（nnU-Net），并在 10 名患者身上进行了测试。评估指标包括骰子相似系数（DSC）、召回率、精确度和 F1-分数。CNN 的分割结果与两名观察者的分割结果进行了比较。结果nnU-Net对选择性淋巴结进行了自动分割，DSC中位数为0.72，召回率为0.76，精确度为0.1：0.76，精确度：0.78，F1-分数：0.78。与两位观察者相比，CNN 的召回率更高（p = 0.002）。结论 nnU-Net 能够自动分割 MRI 上的单个淋巴结。使用 nnU-Net 的淋巴结检测率高于人工分割。需要重新训练 nnU-Net 才能将网络成功转移到另一家医疗中心。

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引用次数: 0

Evaluation of deep learning-based target auto-segmentation for Magnetic Resonance Imaging-guided cervix brachytherapy 评估基于深度学习的目标自动分割技术在磁共振成像引导下的宫颈近距离治疗中的应用

IF 3.4 Q2 ONCOLOGY

Physics and Imaging in Radiation Oncology

Pub Date : 2024-10-01 DOI: 10.1016/j.phro.2024.100669

Rita Simões, Eva C. Rijkmans, Eva E. Schaake, Marlies E. Nowee, Sandra van der Velden, Tomas Janssen

Background and purpose

The target structures for cervix brachytherapy are segmented by radiation oncologists using imaging and clinical information. At the first fraction, this is performed manually from scratch. For subsequent fractions the first fraction segmentations are rigidly propagated and edited manually. This process is time-consuming while patients wait immobilized. In this work, we evaluate the potential clinical impact of using population-based and patient-specific auto-segmentations as a starting point for target segmentation of the second fraction.

Materials and method

For twenty-eight patients with locally advanced cervical cancer, treated with MRI-guided brachytherapy, auto-segmentations were retrospectively generated for the second fraction image using two approaches: 1) population-based model, 2) patient-specific models fine-tuned on first fraction information. A radiation oncologist manually edited the auto-segmentations to assess model-induced bias. Pairwise geometric and dosimetric comparisons were performed for the automatic, edited and clinical structures. The time spent editing the auto-segmentations was compared to the current clinical workflow.

Results

The edited structures were more similar to the automatic than to the clinical structures. The geometric and dosimetric differences between the edited and the clinical structures were comparable to the inter-observer variability investigated in literature. Editing the auto-segmentations was faster than the manual segmentation performed during our clinical workflow. Patient-specific auto-segmentations required less edits than population-based structures.

Conclusions

Auto-segmentation introduces a bias in the manual delineations but this bias is clinically irrelevant. Auto-segmentation, particularly patient-specific fine-tuning, is a time-saving tool that can improve treatment logistics and therefore reduce patient burden during the second fraction of cervix brachytherapy.

背景和目的宫颈近距离放射治疗的目标结构是由放射肿瘤专家利用成像和临床信息进行分割的。第一次分割时，需要从头开始手工操作。在随后的分次治疗中，第一次分次分割的结果会被硬性传播并进行人工编辑。这一过程非常耗时，而患者只能静静地等待。在这项工作中，我们评估了使用基于人群和患者特异性的自动分割作为第二部分目标分割起点的潜在临床影响。材料和方法对于 28 位接受 MRI 引导近距离放射治疗的局部晚期宫颈癌患者，我们使用两种方法对第二部分图像进行了自动分割：1）基于人群的模型；2）根据第一部分信息微调的患者特定模型。放射肿瘤学家手动编辑自动分割，以评估模型引起的偏差。对自动结构、编辑结构和临床结构进行成对几何和剂量比较。结果编辑后的结构与自动结构的相似程度高于临床结构。编辑结构与临床结构之间的几何和剂量测定差异与文献中研究的观察者间差异相当。与临床工作流程中的手动分割相比，编辑自动分割的速度更快。结论：自动分割会给手动划分带来偏差，但这种偏差与临床无关。自动分区，尤其是针对患者的微调，是一种节省时间的工具，可以改善治疗流程，从而减轻宫颈近距离治疗第二部分的患者负担。

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引用次数: 0

Monte Carlo simulated correction factors for high dose rate brachytherapy postal dosimetry audit methodology 蒙特卡罗模拟高剂量率近距离放射邮政剂量测定审计方法的校正系数

IF 3.4 Q2 ONCOLOGY

Physics and Imaging in Radiation Oncology

Pub Date : 2024-10-01 DOI: 10.1016/j.phro.2024.100657

Krzysztof Chelminski , Alexis Dimitriadis , Roua Abdulrahim , Pavel Kazantsev , Evelyn Granizo-Roman , Jonathan Kalinowski , Shirin Abbasi Enger , Godfrey Azangwe , Mauro Carrara , Jamema Swamidas

Background and Purpose

Full-scatter conditions in water are impractical for postal dosimetry audits in brachytherapy. This work presents a method to obtain correction factors that account for deviations from full-scatter water-equivalent conditions for a small plastic phantom.

Material and Methods

A 16 × 8 × 3 cm phantom (PMMA) with a radiophotoluminescent dosimeter (RPLD) at the centre and two catheters on either side was simulated using Monte Carlo (MC) to calculate correction factors accounting for the lack of scatter, non-water equivalence of the RPLD and phantom, source model and backscatter for HDR ⁶⁰Co and ¹⁹²Ir sources.

Results

The correction factors for non-water equivalence, lack of full scatter, and the use of PMMA were 1.062 ± 0.013, 1.059 ± 0.008 and 0.993 ± 0.009 for ¹⁹²Ir and 1.129 ± 0.005, 1.009 ± 0.005 and 1.005 ± 0.005 for ⁶⁰Co respectively. Water-equivalent backscatter thickness of 5 cm was found to be adequate and increasing thickness of backscatter did not have an influence on the RPLD dose. The mean photon energy in the RPLD for four HDR ¹⁹²Ir sources was 279 ± 2 keV in full scatter conditions and 295 ± 1 keV in the audit conditions. For ⁶⁰Co source the corresponding mean energies were 989 ± 1 keV and 1022 ± 1 keV respectively.

Conclusions

Correction factors were obtained through the MC simulations for conditions deviating from TG-43, including the amount of back scatter, and the optimum audit set up. Additionally, the influence of different source models on the correction factors was negligible and demonstrates their generic applicability.

背景和目的水中的全散射条件对于近距离放射治疗中的邮政剂量测定审核来说是不切实际的。材料和方法使用蒙特卡洛（Monte Carlo，MC）模拟了一个 16 × 8 × 3 厘米的模型（PMMA），模型中心有一个放射性光致发光剂量计（RPLD），两侧有两根导管，计算出校正系数，校正系数考虑了散射不足、RPLD 和模型的非水等效性、放射源模型以及 HDR 60Co 和 192Ir 放射源的反向散射。结果对于 192Ir 和 60Co，非水等效、缺乏完全散射和使用 PMMA 的校正系数分别为 1.062 ± 0.013、1.059 ± 0.008 和 0.993 ± 0.009，对于 192Ir 和 60Co，分别为 1.129 ± 0.005、1.009 ± 0.005 和 1.005 ± 0.005。研究发现，5 厘米的水等效后向散射厚度是足够的，增加后向散射厚度对 RPLD 剂量没有影响。在全散射条件下，4 个 HDR 192Ir 源在 RPLD 中的平均光子能量为 279 ± 2 keV，在审计条件下为 295 ± 1 keV。对于 60Co 光源，相应的平均能量分别为 989 ± 1 keV 和 1022 ± 1 keV。结论通过 MC 模拟获得了偏离 TG-43 条件的校正因子，包括后向散射量和最佳审核设置。此外，不同源模型对校正因子的影响可以忽略不计，这也证明了校正因子的通用性。

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引用次数: 0

Feasibility and potential clinical benefit of dose de-escalation in stereotactic ablative radiotherapy for lung cancer lesions with ground glass opacities 立体定向消融放疗剂量递减治疗肺癌磨玻璃混浊的可行性及潜在临床效益。

IF 3.4 Q2 ONCOLOGY

Physics and Imaging in Radiation Oncology

Pub Date : 2024-10-01 DOI: 10.1016/j.phro.2024.100681

Carla Cases , Meritxell Mollà , Marcelo Sánchez , Mariana Benegas , Marc Ballestero , Sergi Serrano-Rueda , Gabriela Antelo , Carles Gomà

Introduction

Treatment of neoplasic lung nodules with ground glass opacities (GGO) faces two primary challenges. First, the standard practice of treating GGOs as solid nodules, which effectively controls the tumor locally, but might increase associated toxicities. The second is the potential for dose calculation errors related to increased heterogeneity. This study addresses the optimization of a dose de-escalation regime for stereotactic ablative radiotherapy (SABR) for GGO lesions.

Materials and Methods

We used the CT scans of 35 patients (40 lesions) with some degree of GGO component treated at our institution between 2017 and 2021. We first assessed the dose calculation accuracy as a function of the GGO component of the lesion. We then analysed the advantages of a dose de-escalation regime in terms of lung dose reduction (Dmean, V20Gy and V300GyBED3) and plan robustness.

Results

We found a positive correlation between the presence of GGO and the dose calculation errors in a phantom scenario. These differences are reduced for patient data and in the presence of breathing motion. When using a de-escalation regime, significant reductions were achieved in mean lung dose, V20Gy and V300GyBED3. This study also revealed that lower doses in GGO areas lead to more stable fluence patterns, increasing treatment robustness.

Conclusions

The study lays the foundation for an eventual use of dose de-escalation in SABR for treating lung lesions with GGO, potentially leading to equivalent local control while reducing associated toxicities. These findings lay the groundwork for future clinical trials.

治疗伴有磨玻璃混浊（GGO）的肿瘤性肺结节面临两个主要挑战。首先，将ggo作为实性结节治疗的标准做法，可以有效地局部控制肿瘤，但可能增加相关的毒性。第二是与异质性增加有关的剂量计算误差的可能性。本研究旨在优化立体定向消融放疗（SABR）治疗GGO病变的剂量递减方案。材料和方法：我们使用了2017年至2021年间在我院治疗的35例不同程度GGO成分患者（40个病变）的CT扫描。我们首先评估了剂量计算准确性作为病变GGO成分的函数。然后，我们分析了剂量递减方案在肺剂量减少（Dmean， V20Gy和v300r00bed3）和计划稳健性方面的优势。结果：我们发现幻像情景中GGO的存在与剂量计算误差呈正相关。这些差异在患者数据和呼吸运动的存在下减少。当使用降级方案时，平均肺剂量、V20Gy和v300r00bed3显著降低。该研究还表明，GGO区域的较低剂量导致更稳定的影响模式，增加了治疗的稳健性。结论：该研究为最终使用剂量递减法在SABR中使用GGO治疗肺部病变奠定了基础，可能导致等效的局部控制，同时减少相关毒性。这些发现为未来的临床试验奠定了基础。

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