Experimental study of beam distortion due to fiducial markers during salvage HIFU in the prostate.
Experimental study of beam distortion due to fiducial markers during salvage HIFU in the prostate.
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DOI：
10.1186/s40349-018-0109-3
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发表时间：
2018
期刊：
影响因子：
--
通讯作者：
E Treeby B
中科院分区：
文献类型：
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作者：
Bakaric M;Martin E;S Georgiou P;T Cox B;Payne H;E Treeby B
前列腺癌通常使用外部射束放射治疗（EBRT）进行治疗。在治疗之前，前列腺通常植入有少量的永久性基准标记，用于在治疗期间监测前列腺的位置。在局部癌症复发的情况下，高强度聚焦超声（HIFU）提供了一种非侵入性挽救治疗选择。然而，迄今为止，基准标记物对HIFU治疗的影响尚未得到彻底研究。本研究的目的是通过实验研究单个EBRT基准标记对使用组织模拟材料（TMM）的HIFU治疗输送效果的影响。基于含有牛血清白蛋白的聚丙烯酰胺水凝胶，开发了具有前列腺声学特性的TMM。每个体模植入圆柱形基准标记，然后使用3.3 MHz聚焦碗HIFU换能器进行超声处理。进行了两组实验。在第一种情况下，在相对于标记的前后或左右轴的不同位置沿着创建单个病变。在第二种情况下，通过光栅扫描创建更大的消融体积。使用覆盖在体模上的毫米网格评估消融体积的大小和位置。当换能器焦点位于标记前7 mm、标记后18 mm或标记外侧3 mm内时，标记对HIFU损伤位置和大小的影响显著。除此之外，生成的病变未受影响。当焦点位于标记物前方时，由于反射，病变的大小增加。当病灶位于后方时，病灶大小减小或因阴影而不存在。EBRT基准标记物的存在可能导致由于到达焦点的能量减少而导致标记物之外的治疗不足区域，以及由于反射而导致标记物前面的治疗过度区域。取决于靶向区域的位置和标记物的分布，这两种效应可能是不期望的并且降低治疗功效。进一步的工作是必要的，以调查这些结果是否表明有必要重新考虑患者的选择和治疗计划的前列腺挽救性高强度聚焦超声EBRT失败后。
Prostate cancer is frequently treated using external beam radiation therapy (EBRT). Prior to therapy, the prostate is commonly implanted with a small number of permanent fiducial markers used to monitor the position of the prostate during therapy. In the case of local cancer recurrence, high-intensity focused ultrasound (HIFU) provides a non-invasive salvage treatment option. However, the impact of the fiducial markers on HIFU treatment has not been thoroughly studied to date. The objective of this study was to experimentally investigate the effect of a single EBRT fiducial marker on the efficacy of HIFU treatment delivery using a tissue-mimicking material (TMM). A TMM with the acoustic properties of the prostate was developed based on a polyacrylamide hydrogel containing bovine serum albumin. Each phantom was implanted with a cylindrical fiducial marker and then sonicated using a 3.3 MHz focused bowl HIFU transducer. Two sets of experiments were performed. In the first, a single lesion was created at different positions along either the anteroposterior or left-right axes relative to the marker. In the second, a larger ablation volume was created by raster scanning. The size and position of the ablated volume were assessed using a millimetre grid overlaid on the phantom. The impact of the marker on the position and size of the HIFU lesion was significant when the transducer focus was positioned within 7 mm anteriorly, 18 mm posteriorly or within 3 mm laterally of the marker. Beyond this, the generated lesion was not affected. When the focus was anterior to the marker, the lesion increased in size due to reflections. When the focus was posterior, the lesion decreased in size or was not present due to shadowing. The presence of an EBRT fiducial marker may result in an undertreated region beyond the marker due to reduced energy arriving at the focus, and an overtreated region in front of the marker due to reflections. Depending on the position of the targeted regions and the distribution of the markers, both effects may be undesirable and reduce treatment efficacy. Further work is necessary to investigate whether these results indicate the necessity to reconsider patient selection and treatment planning for prostate salvage HIFU after failed EBRT.