A body mass index-based method for “MR-only” abdominal MR-guided adaptive radiotherapy

IF 2.4 4区医学 Q2 RADIOLOGY, NUCLEAR MEDICINE & MEDICAL IMAGING Zeitschrift fur Medizinische Physik Pub Date : 2024-08-01 DOI:10.1016/j.zemedi.2022.12.001

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Abstract

Purpose

Dose calculation for MR-guided radiotherapy (MRgRT) at the 0.35 T MR-Linac is currently based on deformation of planning CTs (defCT) acquired for each patient. We present a simple and robust bulk density overwrite synthetic CT (sCT) method for abdominal treatments in order to streamline clinical workflows.

Method

Fifty-six abdominal patient treatment plans were retrospectively evaluated. All patients had been treated at the MR-Linac using MR datasets for treatment planning and plan adaption and defCT for dose calculation. Bulk density CTs (4M-sCT) were generated from MR images with four material compartments (bone, lung, air, soft tissue). The relative electron densities (RED) for bone and lung were extracted from contoured CT structure average REDs. For soft tissue, a correlation between BMI and RED was evaluated. Dose was recalculated on 4M-sCT and compared to dose distributions on defCTs assessing dose differences in the PTV and organs at risk (OAR).

Results

Mean RED of bone was 1.17 ± 0.02, mean RED of lung 0.17 ± 0.05. The correlation between BMI and RED for soft tissue was statistically significant (p < 0.01). PTV dose differences between 4M-sCT and defCT were D_mean: −0.4 ± 1.0%, D_1%: −0.3 ± 1.1% and D_95%: −0.5 ± 1.0%. OARs showed D_2%: −0.3 ± 1.9% and D_mean: −0.1 ± 1.4% differences. Local 3D gamma index pass rates (2%/2mm) between dose calculated using 4M-sCT and defCT were 96.8 ± 2.6% (range 89.9–99.6%).

Conclusion

The presented method for sCT generation enables precise dose calculation for MR-only abdominal MRgRT.

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基于体重指数的 "纯磁共振 "腹部磁共振引导自适应放射治疗方法。

目的：目前，在 0.35 T MR-Linac 上进行磁共振引导放疗 (MRgRT) 的剂量计算基于为每位患者获取的计划 CT（defCT）的变形。我们针对腹部治疗提出了一种简单、稳健的体密度覆盖合成 CT（sCT）方法，以简化临床工作流程：方法：我们对 56 例腹部患者的治疗计划进行了回顾性评估。所有患者均在磁共振Linac接受过治疗，治疗计划和计划调整使用磁共振数据集，剂量计算使用defCT。大体密度 CT（4M-sCT）由四个物质区（骨、肺、空气、软组织）的磁共振图像生成。骨和肺的相对电子密度（RED）是从轮廓 CT 结构平均 RED 中提取的。对于软组织，则评估了 BMI 与 RED 之间的相关性。在 4M-sCT 上重新计算剂量，并与 defCT 上的剂量分布进行比较，评估 PTV 和危险器官 (OAR) 的剂量差异：结果：骨的平均 RED 为 1.17 ± 0.02，肺的平均 RED 为 0.17 ± 0.05。体重指数（BMI）与软组织 RED 之间的相关性具有统计学意义（P 平均值：-0.4 ± 1.0）：-0.4 ± 1.0%, D1%:-0.3±1.1%，D95%：-0.5 ± 1.0%.OAR 显示 D2%：-0.3 ± 1.9%，D95%：-0.5 ± 1.0%：-0.3 ± 1.9% 和 Dmean：差异为-0.1 ± 1.4%。使用4M-sCT和defCT计算的剂量之间的局部三维伽马指数通过率（2%/2mm）为96.8 ± 2.6%（范围89.9-99.6%）：结论：所介绍的 sCT 生成方法可精确计算仅磁共振腹部 MRgRT 的剂量。

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来源期刊

Zeitschrift fur Medizinische Physik 医学-核医学

CiteScore

3.70

自引率

10.00%

发文量

审稿时长

65 days

期刊介绍： Zeitschrift fur Medizinische Physik (Journal of Medical Physics) is an official organ of the German and Austrian Society of Medical Physic and the Swiss Society of Radiobiology and Medical Physics.The Journal is a platform for basic research and practical applications of physical procedures in medical diagnostics and therapy. The articles are reviewed following international standards of peer reviewing. Focuses of the articles are: -Biophysical methods in radiation therapy and nuclear medicine -Dosimetry and radiation protection -Radiological diagnostics and quality assurance -Modern imaging techniques, such as computed tomography, magnetic resonance imaging, positron emission tomography -Ultrasonography diagnostics, application of laser and UV rays -Electronic processing of biosignals -Artificial intelligence and machine learning in medical physics In the Journal, the latest scientific insights find their expression in the form of original articles, reviews, technical communications, and information for the clinical practice.