Background/Objectives: Stereotactic body radiotherapy is frequently used in patients with adrenal metastases. Motion of adherent radiosensitive organs at risk (OARs) and tumors influence OAR toxicity and tumor control. Online-adaptive Magnetic Resonance-guided radiotherapy (MRgRT) can address and mitigate interfractional changes. However, the impact of intrafractional variations in adrenal MRgRT is unknown. Methods: A total of 23 patients with 24 adrenal metastases were treated with MRgRT. After daily plan adaptation and before beam application, an additional (preRT) 3d MRI was acquired. PreRT target volumes and OARs were retrospectively recontoured in 200 fractions. The delivered, online-adapted treatment plans, as well as non-adapted baseline plans, were calculated on these re-contoured structures to quantify the dosimetric impact of intrafractional variations on target volume coverage and OAR doses with and without online adaptation. Normal tissue complication probabilities (NTCPs) were calculated. Results: The median time between the two MRIs was 56.4 min. GTV and PTV coverage (dose to 95% of the PTV, D95%, and volume covered by 100% of the prescription dose, V100%) were significantly inferior in the preRT plans. GTV Dmeanwas significantly impaired in left-sided metastases, but not in right-sided metastases. Compared to non-adapted preRT plans, adapted preRT plans were still significantly superior for all GTV and PTV metrics. Intrafractional violations of OAR constraints were frequent. D0.5cc and the volume exposed to the near-maximum dose constraint were significantly higher in the preRT plans. The volume exposed to the D0.5cc constraints in single fractions escalated up to 1.5 cc for the esophagus, 3.2 cc for the stomach, 5.3 cc for the duodenum and 7.3 cc for the bowel. This led to significantly elevated NTCPs for the stomach, bowel and duodenum. Neither PTV D95%, nor gastrointestinal OAR maximum doses were significantly impaired by longer fraction duration. Conclusions: Intrafractional motion in adrenal MRgRT caused significant impairment of target volume coverage (D95% and V100%), potentially undermining local control. Frequent violation of gastrointestinal OAR constraints led to elevated NTCP. Compared to non-adaptive treatment, online adaptation still highly improved GTV and PTV coverage.
背景/目的：立体定向放射治疗常用于肾上腺转移瘤患者。邻近风险器官（OARs）与肿瘤的运动会影响OAR毒性及肿瘤控制。在线自适应磁共振引导放射治疗（MRgRT）可应对并减轻分次间变化，但肾上腺MRgRT中分次内变异的影响尚不明确。方法：共23例患者的24处肾上腺转移灶接受MRgRT治疗。每日计划调整后、照射实施前，额外采集一次（放疗前）三维MRI。对200个治疗分次的放疗前靶区及OARs进行回顾性重勾画。基于这些重勾画结构，分别计算已实施的在线自适应治疗计划及非自适应基线计划的剂量学参数，以量化分次内变异对靶区覆盖度和OAR剂量的影响，并计算正常组织并发症概率（NTCP）。结果：两次MRI采集的中位时间间隔为56.4分钟。放疗前计划的GTV和PTV覆盖度（95%PTV受照剂量D95%、处方剂量100%覆盖体积V100%）显著降低。左侧转移灶的GTV平均剂量显著受损，右侧转移灶则无此现象。相较于非自适应放疗前计划，自适应放疗前计划在所有GTV和PTV指标上仍保持显著优势。分次内OAR剂量限制频繁超标：放疗前计划的0.5立方厘米受照剂量（D0.5cc）及近最大剂量限制暴露体积显著更高。单次治疗中，食管、胃、十二指肠和肠道的D0.5cc限制暴露体积最高分别达1.5立方厘米、3.2立方厘米、5.3立方厘米和7.3立方厘米，导致胃、肠道和十二指肠的NTCP显著升高。治疗分次时长既未显著影响PTV D95%，也未显著影响胃肠道OAR最大剂量。结论：肾上腺MRgRT中的分次内运动导致靶区覆盖度（D95%和V100%）显著受损，可能影响局部控制。胃肠道OAR剂量限制频繁超标导致NTCP升高。相较于非自适应治疗，在线自适应技术仍能显著改善GTV和PTV覆盖度。
肿瘤(癌症)患者之家