背景:MR-Linac的磁共振引导自适应放射治疗(MRgART)允许对基于MR的合成CT(sCT)图像进行计划优化,根据患者的日常解剖结构调整目标和危险器官。相反,传统的直线加速器图像引导放射治疗(IGRT)涉及感兴趣的区域与日常解剖结构的刚性重新排列,随后交付参考计算机断层扫描(CT)计划。本研究旨在评估MRgART与IGRT对直肠癌患者短期放疗的疗效。同时还评估剂量累积过程以支持研究结果并确定其在提高治疗准确性方面的有效性。
方法:19例直肠癌患者接受1.5特斯拉MR-Linac治疗,处方剂量为25Gy(5Gyx5),并通过基于在线MR的sCT图像的计划优化进行每日适应性放疗,纳入本回顾性研究。对于每个调整后的计划([公式:见正文]),在与参考CT图像进行刚性配准后,通过在每日基于MR的sCT图像上重新计算参考CT计划来生成第二个计划([公式:参见正文]),以模拟IGRT工作流程。对每个分数比较[公式:见文本]和[公式:见文本]的剂量测定。对于两个工作流程,评估第一和最后部分的累积剂量。使用剂量-体积直方图参数比较每单个部分的剂量测定和累积剂量。
结果:将用MRgART递送的95级分与相应的模拟IGRT级分进行比较。所有MRgART部分均满足目标临床要求。IGRT处理没有达到预期的目标覆盖率的63分94(67.0%),13个馏分显示V95中位数百分比下降2.78%(范围,1.65-4.16%),和超过V107%阈值的55个分数,中值为15.4cc(范围,6.0-43.8cc)。对于膀胱,[公式:见正文]中值对于适应性部分为18.18Gy,对于IGRT部分为19.60Gy。同样,小肠的中值[公式:见正文]分别为23.40Gy和25.69Gy,分别。在自适应工作流程的第一个或最后一个分数上累积的剂量没有观察到统计学上的显着差异。结果与单一适应分数一致。相比之下,IGRT工作流程中的累积剂量显示出显着的变化,从而减轻了高剂量约束,然而,超过一半的患者仍未达到临床要求.
结论:用于短程直肠癌治疗的MRgART确保所输送的剂量与计划剂量的每个部分相匹配,并且结果通过剂量累积过程得到证实,因此,这似乎是多余的。相比之下,IGRT可能导致目标剂量差异和对处于风险约束的器官的不依从性,并且剂量累积仍然可以突出显著的剂量学差异。
BACKGROUND: Magnetic resonance-guided adaptive radiotherapy (MRgART) at MR-Linac allows for plan optimisation on the MR-based synthetic CT (sCT) images, adjusting the target and organs at risk according to the patient\'s daily anatomy. Conversely, conventional linac image-guided radiotherapy (IGRT) involves rigid realignment of regions of interest to the daily anatomy, followed by the delivery of the reference computed tomography (CT) plan. This study aims to evaluate the effectiveness of MRgART versus IGRT for rectal cancer patients undergoing short-course radiotherapy, while also assessing the dose accumulation process to support the findings and determine its usefulness in enhancing treatment accuracy.
METHODS: Nineteen rectal cancer patients treated with a 1.5 Tesla MR-Linac with a prescription dose of 25 Gy (5 Gy x 5) and undergoing daily adapted radiotherapy by plan optimization based on online MR-based sCT images, were included in this retrospective study. For each adapted plan ([Formula: see text]), a second plan ([Formula: see text]) was generated by recalculating the reference CT plan on the daily MR-based sCT images after rigid registration with the reference CT images to simulate the IGRT workflow. Dosimetry of [Formula: see text] and[Formula: see text]was compared for each fraction. Cumulative doses on the first and last fractions were evaluated for both workflows. The dosimetry per single fraction and the cumulative doses were compared using dose-volume histogram parameters.
RESULTS: Ninety-five fractions delivered with MRgART were compared to corresponding simulated IGRT fractions. All MRgART fractions fulfilled the target clinical requirements. IGRT treatments did not meet the expected target coverage for 63 out of 94 fractions (67.0%), with 13 fractions showing a V95 median point percentage decrease of 2.78% (range, 1.65-4.16%), and 55 fractions exceeding the V107% threshold with a median value of 15.4 cc (range, 6.0-43.8 cc). For the bladder, the median [Formula: see text] values were 18.18 Gy for the adaptive fractions and 19.60 Gy for the IGRT fractions. Similarly the median [Formula: see text] values for the small bowel were 23.40 Gy and 25.69 Gy, respectively. No statistically significant differences were observed in the doses accumulated on the first or last fraction for the adaptive workflow, with results consistent with the single adaptive fractions. In contrast, accumulated doses in the IGRT workflow showed significant variations mitigating the high dose constraint, nevertheless, more than half of the patients still did not meet clinical requirements.
CONCLUSIONS: MRgART for short-course rectal cancer treatments ensures that the dose delivered matches each fraction of the planned dose and the results are confirmed by the dose accumulation process, which therefore seems redundant. In contrast, IGRT may lead to target dose discrepancies and non-compliance with organs at risk constraints and dose accumulation can still highlight notable dosimetric differences.