Posiewnik Michał, Piotrowski Tomasz
Department of Medical Physics, Gdynia Oncology Centre, Gdynia, Poland.
Department of Electroradiology, Poznan University of Medical Sciences, Poznań, Poland.
Contemp Oncol (Pozn). 2021;25(4):249-253. doi: 10.5114/wo.2021.112518. Epub 2022 Jan 5.
The aim was to validate the dosimetric and geometric accuracy of radiotherapy treatment plans for prostate cancer based on magnetic resonance (MR) imaging only and a solution based on computed tomography (CT) supported by MR imaging.
We used CT and MR images of ten prostate cancer patients implanted with three fiducial markers (FM) in the prostate gland. Rigid registration based on FM was performed to assess the fusion accuracy between MR and CT images. The differences between prostate contours (clinical target volume - CTV) on CT (CTV) and MR (CTV) images were scored using the Dice similarity coefficient and directly comparing the outlined volumes. The volumetric modulated arc therapy plans were designed and optimised on synthetic CT (sCT) to obtain the dose distribution for the MR-only solution. In the next step, the sCT images were replaced by conventional CT images and the plans were recalculated. The doses obtained on sCT and CT were compared by direct dose subtraction and the gamma method.
The averaged fiducial registration error was equal to 0.5 mm. All CTV volumes were significantly bigger than corresponding CTV delineated on MR images ( = 0.005). The direct dose comparison shows that for 97.1% of patients' bodies, the differences were smaller than 0.1%. The average gamma passing rates were higher than 0.970.
MR imaging allows for a more precise delineation of the prostate compared to CT imaging. The workflow of plan preparation based on MR and CT is burdened with an FM registration error that is eliminated by an MR-only solution with no compromise on dose distribution.
目的是验证仅基于磁共振（MR）成像以及基于MR成像支持的计算机断层扫描（CT）解决方案的前列腺癌放射治疗计划的剂量学和几何精度。
我们使用了十位前列腺癌患者的CT和MR图像，这些患者在前列腺中植入了三个基准标记（FM）。基于FM进行刚性配准以评估MR和CT图像之间的融合精度。使用Dice相似系数并直接比较勾勒出的体积来对CT（CTV）和MR（CTV）图像上前列腺轮廓（临床靶体积 - CTV）之间的差异进行评分。在合成CT（sCT）上设计并优化容积调强弧形治疗计划，以获得仅基于MR解决方案的剂量分布。下一步，将sCT图像替换为传统CT图像并重新计算计划。通过直接剂量减法和伽马方法比较在sCT和CT上获得的剂量。
平均基准配准误差等于0.5毫米。所有CTV体积均明显大于在MR图像上勾勒出的相应CTV（ = 0.005）。直接剂量比较表明，对于97.1%的患者身体，差异小于0.1%。平均伽马通过率高于0.970。
与CT成像相比，MR成像能够更精确地勾勒前列腺。基于MR和CT的计划准备工作流程存在FM配准误差，而仅基于MR的解决方案可消除该误差，且不会对剂量分布造成影响。
