在前列腺癌放射治疗 (RT) 中，直肠靠近前列腺，这对剂量测定提出了重大挑战，导致直肠剂量较高并产生有害的副作用。直肠周围组织间距通过机械分离这些器官来减少直肠剂量和胃肠道毒性。人们已经探索了多种材料用作直肠间隔物，最近是一种稳定的透明质酸（HA）凝胶，与聚乙二醇不同，它可以形成有意的形状，并保留该形状的定义，同时保持柔性。 PEG）水凝胶。本研究评估了间隔物的剂量影响，包括形状对称性、不同位置的分离程度以及空间的时间稳定性。我们的目标是为这种可雕刻垫片的最佳使用提供物理指导。对一项 13 中心前瞻性随机试验 (NCT04189913) 的数据进行了二次分析，该试验涉及 136 名患者，并在 CT/CT 上进行了集中审查的治疗计划。接受 HA 间隔植入物前后的 MR 模拟扫描。患者接受 60 Gy 的前列腺治疗，分 20 次进行。在本研究中，Python 软件用于自动处理 DICOM RTstruct 和 RTdose 文件，有助于详细分析垫片对解剖位移和剂量测定结果的影响。重建完整的剂量体积直方图 (DVH)，并在植入前后组合成复合群体 DVH，并根据试验报告的剂量点进行验证。患者被分为相似的分离和对称组，并测试其复合 DVH 的差异的显着性。通过比较连续 MRI 图像并计算 RT 后模拟和 3 个月随访时四个轴向平面轮廓之间的距离，研究了间隔器的稳定性。HA 间隔器的引入显着增强了直肠保护，如下所示平均直肠积分剂量减少超过 6 Gy。观察到高种植体对称率 (>95%)，表明侧向垫片放置接近最佳。在上下覆盖范围中，这项研究与许多其他研究一样，在上部范围内发现间距最大，但在前列腺尖部水平下部变得更加可变。这使得可以将顶点作为剂量学关注的特定区域进行研究。稳定性评估证实，在模拟和 RT 后 3 个月之间，垫片保持其位置和尺寸，这意味着治疗期间几何形状稳定，仅观察到最小的分离变化。使用 Kruskal-Wallis 检验的统计分析显示，下平面和顶端平面的较大分离与改善的剂量结果（包括 rV30Gy）存在显着相关性。在前列腺放疗中使用稳定的 HA 间隔物可有效增强前列腺-直肠分离，从而显着保留直肠没有不良的剂量妥协。这项研究强调了战略位置和形状的作用，特别是从基部到前列腺尖的距离 > 1 厘米。当与试验中使用的治疗计划技术相结合，在间隔器上创建陡峭的剂量梯度时，这些发现阐明了 HA 间隔器临床实施中可以预期的剂量测定结果。这与前列腺癌大分割治疗方案的演变尤其相关。© 2024 作者。 《医学物理学》由 Wiley periodicals LLC 代表美国医学物理学家协会出版。

The proximity of the rectum to the prostate in radiation therapy (RT) for prostate cancer presents a significant dosimetric challenge, leading to high rectal doses and resulting in detrimental side effects. Perirectal tissue spacing reduces rectal dose and gastrointestinal toxicities by mechanically separating these organs. A variety of materials have been explored for use as rectal spacers, most recently, a stabilized hyaluronic acid (HA) gel, which can be formed into deliberate a shape, and retains the definition of that shape, while remaining flexible, unlike polyethylene glycol (PEG) hydrogels.This study evaluates the dosimetric impact of the spacer, including shape symmetry, the degree of separation at different locations, and the temporal stability of the space. Our goal is to provide physics-informed guidance on the optimal use of this sculptable spacer.A secondary analysis was performed on data from a 13-center prospective randomized trial (NCT04189913), involving 136 patients with centrally-reviewed treatment plans conducted on CT/MR simulation scans before and after receiving HA spacer implants. Patients were treated with 60 Gy in 20 fractions to the prostate. For this study, python software was utilized for automated processing of DICOM RTstruct and RTdose files, facilitating detailed analysis of the spacer's impact on anatomical displacement and dosimetric outcomes. Complete dose-volume histograms (DVHs) were reconstructed, and combined into composite population DVHs before and after implant, verified against trial-reported dose points. Patients were divided into similar groups of separation and symmetry, and differences in their composite DVHs were tested for significance. Stability of the spacer was studied by comparing serial MRI images and by computing the distance between contours at four axial planes, at simulation and 3-month follow-up, post RT.The introduction of the HA spacer significantly enhanced rectal sparing, as evidenced by a reduction in the mean rectal integral dose by over 6 Gy. High rates of implant symmetry (>95%) were observed, indicating nearly optimal lateral spacer placement. In superior-inferior coverage, this study like many others, saw the spacing largest at the superior extent but becoming more variable inferiorly at the level of the prostate apex. This allowed study of the apex as a specific area for dosimetric concern. Stability assessments confirmed that the spacer maintained its position and dimensions between the simulation and the 3-month post-RT, implying stable geometry during treatment, with only minimal separation changes observed. Statistical analysis using the Kruskal-Wallis test revealed significant correlations of larger separations at the inferior and apical planes with improved dosimetric outcomes, including rV30Gy.The use of a stabilized HA spacer in prostate RT effectively enhances prostate-rectum separation, leading to significant rectal sparing without undesirable dose compromises. This study underscores the role of strategic placement and shape, specifically including > 1 cm separation from the base down to the prostate apex. When combined with the treatment planning techniques used in the trial to create a steep dosimetric gradient across the spacer, these findings elucidate the dosimetric outcomes that can be expected in the clinical implementation of HA spacer. This is particularly relevant in the evolution of hypofractionated treatment regimens for prostate cancer therapy.© 2024 The Author(s). Medical Physics published by Wiley Periodicals LLC on behalf of American Association of Physicists in Medicine.