Sato Kimihiko, Kanai Takayuki, Lee Sung Hyun, Miyasaka Yuya, Chai Hongbo, Souda Hikaru, Iwai Takeo, Sato Ryuji, Goto Naoki, Kawamura Tsukasa
Department of Heavy Particle Medical Science, Yamagata University Graduate School of Medical Science, 2-2-2 Iidanishi, Yamagata, 990-9585, Japan.
Department of Radiology, Nihonkai General Hospital, 30 Akiho-chou, Sakata, Yamagata, 998-8501, Japan.
Radiol Phys Technol. 2022 Dec;15(4):367-378. doi: 10.1007/s12194-022-00676-0. Epub 2022 Aug 30.
This study aimed to develop a new method to quantitatively analyze body shape changes in patients during radiotherapy without additional radiation exposure using an optical surface tracking system. This method's accuracy was evaluated using a cubic phantom with a known shift. Surface images of three-dimensionally printed phantoms, which simulated the head and neck shapes of real patients before and after treatment, were used to create a deformation surface area histogram. The near-maximum deformation value covering an area of 2 cm in the surface image (Def-2cm) was calculated. A volumetric modulated arc therapy (VMAT) plan was also created on the pre-treatment phantom, and the dose distribution was recalculated on the post-treatment phantom to compare the dose indices. Surface images of four patients were analyzed to evaluate Def-2cm and examine whether this method can be used in clinical cases. Experiments with the cubic phantom resulted in a mean deformation error of 0.08 mm. With head and neck phantoms, the Def-2cm value was 17.5 mm, and the dose that covered 95% of the planning target volume in the VMAT plan decreased by 11.7%, indicating that deformation of the body surface may affect the dose distribution. Although analysis of the clinical data showed no clinically relevant deformation in any of the cases, slight skin sagging and respiratory changes in the body surface were observed. The proposed method can quantitatively and accurately evaluate the deformation of a body surface. This method is expected to be used to make decisions regarding modifications to treatment plans.
本研究旨在开发一种新方法，利用光学表面跟踪系统在不增加额外辐射暴露的情况下，定量分析放疗期间患者身体形状的变化。使用具有已知位移的立方体模体评估该方法的准确性。利用三维打印模体的表面图像（模拟真实患者治疗前后的头颈部形状）创建变形表面积直方图。计算表面图像中覆盖面积为2 cm的近最大变形值（Def-2cm）。还在治疗前模体上创建容积调强弧形治疗（VMAT）计划，并在治疗后模体上重新计算剂量分布以比较剂量指数。分析了4例患者的表面图像，以评估Def-2cm并检验该方法是否可用于临床病例。对立方体模体进行的实验得出平均变形误差为0.08 mm。对于头颈部模体，Def-2cm值为17.5 mm，VMAT计划中覆盖95%计划靶体积的剂量降低了11.7%，表明体表变形可能影响剂量分布。虽然对临床数据的分析显示在任何病例中均未出现临床相关变形，但观察到体表有轻微皮肤下垂和呼吸变化。所提出的方法能够定量且准确地评估体表变形。预计该方法将用于做出有关修改治疗计划的决策。
