Biomaterials Translational Research Center, China Medical University Hospital, Taichung City, Taiwan, R.O.C.
Department of Biomedical Imaging and Radiological Science, China Medical University, Taichung City, Taiwan, R.O.C.
PLoS One. 2019 Feb 21;14(2):e0212546. doi: 10.1371/journal.pone.0212546. eCollection 2019.
Intensity-modulated radiotherapy and volumetric modulated arc therapy are modern radiation therapy technologies that can create the desired dose distribution by multileaf collimator movement and dose-rate control. However, the homogeneous dose delivery of small-field irradiation techniques shows disagreement with that of treatment planning system. The removal of the flattening filter by flattening filter free (FFF) beam irradiation increases dose conformity and further reduces treatment delivery time in radiosurgery. This study aims to investigate the dose distribution of FFF and flattened beams for small-field irradiation by using the 3D gel dosimeter. The N-isopropylacrylamide (NIPAM) polymer gel dosimeter was employed to record the 3D dose distribution. In addition, flattened and FFF beams were compared using the gamma evaluation technique. The use of an FFF accelerator resulted in excellent radiation treatments with short delivery times and low doses to normal tissues and organs. Results also showed that the passing rate increased with the decrease of field size (30 × 30, 20 × 20, and 10 × 10 mm2) at post-irradiation times of 24, 48, 72, and 96 h. The passing rates for each field size were retained at the same level when gamma criteria, namely, distance-to-agreement (DTA) = 3 mm/dose difference (DD) = 3%, were used. Nevertheless, the passing rates for each field size decreased slowly after 48 h when DTA = 2 mm/DD = 2%. The Wilcoxon signed-rank test was used to determine statistical difference with a significant level of p < 0.05. The passing rates of flattened and FFF beams showed no significant difference. The edge enhancement effect in the flattened beam was more evident than in the FFF beam. The 3D NIPAM gel dosimeter can be used for dose verification of small field for radiation therapy with high dose rate.
强度调制放疗和容积旋转调强放疗是现代放疗技术，通过多叶准直器的运动和剂量率控制来实现所需的剂量分布。然而，小野照射技术的均匀剂量分布与治疗计划系统的结果存在差异。通过使用无均整滤过（FFF）射束，消除了均整滤过器，提高了剂量适形度，并进一步缩短了立体定向放射治疗的治疗时间。本研究旨在使用 3D 凝胶剂量计研究 FFF 和常规射束用于小野照射的剂量分布。使用 N-异丙基丙烯酰胺（NIPAM）聚合物凝胶剂量计记录 3D 剂量分布。此外，还使用伽马评估技术比较了常规射束和 FFF 射束。使用 FFF 加速器可实现出色的放射治疗，治疗时间短，对正常组织和器官的剂量低。结果还表明，随着照射后时间的增加（24、48、72 和 96 h），随着射野尺寸的减小（30×30、20×20 和 10×10 mm2），通过率也随之增加。当伽马标准（即距离一致性（DTA）= 3 mm/剂量差（DD）= 3%）时，每个射野尺寸的通过率都保持在相同水平。然而，当 DTA = 2 mm/DD = 2%时，每个射野尺寸的通过率在 48 h 后缓慢下降。使用 Wilcoxon 符号秩检验确定具有显著水平 p < 0.05 的统计学差异。常规射束和 FFF 射束的通过率没有显著差异。常规射束的边缘增强效果比 FFF 射束更明显。3D NIPAM 凝胶剂量计可用于高剂量率放射治疗中小野的剂量验证。
