Libby B, Ding K, Reardon K, Crandley E, Andrew C, Schneider B
University of Virginia, Charlottesville, VA.
Med Phys. 2012 Jun;39(6Part16):3803. doi: 10.1118/1.4735516.
Vaginal packing for gynecological brachytherapy is used to immobilize the applicator and reduce doses to the bladder and rectum by increasing the separation from the applicator. With the introduction of theRadiadyne Alatus™ balloon packing system, we evaluate further reductions in dose to these structures by increasing the concentration of contrast in the balloon, increasing its attenuation. This evaluation has been performed using the Acuros™ dose calculation algorithm.
A patient with cervical cancer was treated with HDR Ir-192 by insertion of a tandem and ovoid applicator, with the Alatus™ balloon system used for vaginal packing instead of wet gauze. The balloons were filled with distilled water containing 10% Omnipaque contrast. Retrospectively, the balloons were contoured in the BrachyVision™ planning system, and the CT number of the structure set was adjusted to determine the effect of the concentration of the contrast in the balloons on bladder and rectal doses after heterogeneity correction using the Acuros™ algorithm.
Use of 10% Omnipaque solution reduced the bladder and rectal point doses by 6% and 9.5%, respectively, with similar reductions in the D2cc and D1cc for each structure. Overriding the density of the balloon showed that a 50% solution would reduce the doses by 8% and 30%, respectively, due to the positions of the balloons with respect to the applicator dwell positions.
Use of the Alatus™ balloon packing system allows reduction of the bladder and rectal doses both by increasing the distance between the bladder and rectum and the applicators and by increased attenuation of the dose by the use of contrast solution. Optimal dilution of the contrast should take into account both the positive protective effect of the solution as well as any negative artifact that the solution causes in the CT scan, which might obscure the patient's anatomy patient.
妇科近距离放射治疗中使用阴道填塞物来固定施源器，并通过增加与施源器的距离来减少膀胱和直肠所受剂量。随着Radiadyne Alatus™球囊填塞系统的引入，我们通过增加球囊内造影剂浓度、增强其衰减作用，来评估对这些结构所受剂量的进一步降低情况。本评估使用Acuros™剂量计算算法进行。
一名宫颈癌患者接受高剂量率铱-192治疗，通过插入串联卵圆体施源器，并使用Alatus™球囊系统进行阴道填塞，而非湿纱布。球囊内填充含10%欧乃派克造影剂的蒸馏水。回顾性地在BrachyVision™计划系统中勾勒出球囊轮廓，并调整结构集的CT值，以确定使用Acuros™算法进行不均匀性校正后，球囊内造影剂浓度对膀胱和直肠剂量的影响。
使用10%欧乃派克溶液分别使膀胱和直肠的点剂量降低了6%和9.5%，每个结构的D2cc和D1cc也有类似程度的降低。忽略球囊密度显示，由于球囊相对于施源器驻留位置的关系，50%的溶液将分别使剂量降低8%和30%。
使用Alatus™球囊填塞系统可通过增加膀胱和直肠与施源器之间的距离以及利用造影剂溶液增加剂量衰减，来降低膀胱和直肠所受剂量。造影剂的最佳稀释度应同时考虑溶液的正向保护作用以及其在CT扫描中可能造成遮蔽患者解剖结构的任何负面伪影。
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