Miyasaka Yuya, Souda Hikaru, Chai Hongbo, Ishizawa Miyu, Sato Hiraku, Iwai Takeo
Department of Heavy Particle Medical Science, Yamagata University Graduate School of Medical Science, Yamagata, Japan.
Department of Radiology, Faculty of Medicine, Yamagata University, Yamagata, Japan.
Int J Part Ther. 2024 Dec 17;15:100639. doi: 10.1016/j.ijpt.2024.100639. eCollection 2025 Mar.
The study's purpose was to use a simple geometry phantom to validate the deformable image registration (DIR) accuracy and dose warping accuracy in carbon ion radiotherapy (CIRT) and to provide an index for dosimetry in CIRT.
We used geometric and anatomical phantoms provided by AAPM TG-132. The DIRs of 3 different settings were performed between reference and translational images for each phantom. CIRT and photon therapy (3-dimensional conformal radiotherapy and volumetric modulated radiotherapy) treatment plans were transformed by the use of deformation vector fields calculated from the DIR of each setting. The dose distribution calculated on the basis of rigid registration between images was used as the ground truth and compared with the warped dose determined by DIR to evaluate the error.
The photon therapy treatment plans showed a dose warping error of <2% for a DIR error of <2 mm, whereas CIRT showed a dose warping error >10% for the same DIR accuracy. From this, even with similar DIR accuracy, the errors tended to be larger for CIRT than for photon therapy dose distributions. Due to the steepness of the CIRT dose gradient, the dose difference increased by about 5% for a DIR error of 5 mm, which was larger than the 3% dose difference generated for a 5 mm DIR error in photon therapy.
We evaluated the relationship between DIR accuracy and dose warping accuracy in the CIRT dose distribution. Due to the steepness of the dose gradient in CIRT, we concluded that dose warping based on DIR accuracy should be required to be sufficiently higher than that in photon therapy.
本研究旨在使用简单几何体模验证碳离子放射治疗（CIRT）中可变形图像配准（DIR）的准确性和剂量扭曲准确性，并为CIRT剂量测定提供一个指标。
我们使用了美国医学物理师协会（AAPM）TG-132提供的几何和解剖体模。对每个体模的参考图像和平移图像进行了3种不同设置的DIR。通过使用从每种设置的DIR计算出的变形矢量场，对CIRT和光子治疗（三维适形放疗和容积调强放疗）治疗计划进行变换。将基于图像间刚性配准计算的剂量分布用作基准真值，并与DIR确定的扭曲剂量进行比较以评估误差。
对于DIR误差<2 mm，光子治疗计划的剂量扭曲误差<2%，而对于相同的DIR精度，CIRT的剂量扭曲误差>10%。由此可知，即使DIR精度相似，CIRT的误差也往往比光子治疗剂量分布的误差更大。由于CIRT剂量梯度较陡，对于5 mm的DIR误差，剂量差异增加约5%，这大于光子治疗中5 mm DIR误差产生的3%剂量差异。
我们评估了CIRT剂量分布中DIR精度与剂量扭曲精度之间的关系。由于CIRT中剂量梯度较陡，我们得出结论，基于DIR精度的剂量扭曲要求应比光子治疗中的剂量扭曲要求足够高。
