Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional Unidad Monterrey, Vía del Conocimiento 201 Parque de Investigación e Innovación Tecnológica, Apodaca NL CP 66600, Mexico.
Phys Med Biol. 2011 Jan 21;56(2):341-55. doi: 10.1088/0031-9155/56/2/004. Epub 2010 Dec 15.
It has been shown that the use of kilovoltage x-rays in conjunction with a contrast agent incorporated into the tumor can lead to acceptable treatment plans with regard to the absorbed dose distribution produced in the target as well as in the tissue and organs at risk surrounding it. In this work, several key aspects related to the technology and irradiation techniques necessary to clinically implement this treatment modality are addressed by means of Monte Carlo simulation. The Zubal phantom was used to model a prostate radiotherapy treatment, a challenging site due to the depth of the prostate and the presence of bony structures that must be traversed by the x-ray beam on its way to the target. It is assumed that the concentration levels of the enhancing agent present in the tumor are at or below 10 mg per 1 g of tissue. The Monte Carlo code PENELOPE was used to model a commercial x-ray tube having a tungsten target. X-ray energy spectra for several combinations of peak electron energy and added filtration were obtained. For each energy spectrum, a treatment plan was calculated, with the PENELOPE Monte Carlo code, by modeling the irradiation of the patient as 72 independent conformal beams distributed at intervals of 5° around the phantom in order to model a full x-ray source rotation. The Cimmino optimization algorithm was then used to find the optimum beam weight and energy for different treatment strategies. It is shown that for a target dose prescription of 72 Gy covering the whole tumor, the maximum rectal wall and bladder doses are kept below 52 Gy for the largest concentration of contrast agent of 10 mg per 1 g of tissue. It is also shown that concentrations of as little as 5 mg per 1 g of tissue also render dose distributions with excellent sparing of the organs at risk. A treatment strategy to address the presence of non-uniform distributions of the contrast agent in the target is also modeled and discussed.
已经表明，结合肿瘤内掺入的对比剂使用千伏 X 射线可以导致在目标以及周围的组织和器官中产生可接受的吸收剂量分布的治疗计划。在这项工作中，通过蒙特卡罗模拟解决了与该治疗方式的技术和照射技术相关的几个关键方面。使用 Zubal 体模来模拟前列腺放射治疗，由于前列腺的深度以及必须穿过 X 射线束到达目标的骨结构的存在，前列腺是一个具有挑战性的部位。假设肿瘤中增强剂的浓度水平为 1 克组织中存在 10 毫克或以下。使用 PENELOPE 蒙特卡罗代码来模拟具有钨靶的商用 X 射线管。获得了几种峰值电子能量和附加过滤组合的 X 射线能谱。对于每种能谱，使用 PENELOPE 蒙特卡罗代码通过模拟患者的照射来计算治疗计划，通过将 72 个独立的共形射束分布在体模周围每隔 5°的间隔处来模拟全 X 射线源旋转。然后使用 Cimmino 优化算法来找到不同治疗策略的最佳射束权重和能量。结果表明，对于覆盖整个肿瘤的 72 Gy 的靶剂量处方，最大直肠壁和膀胱剂量保持在 52 Gy 以下，对于 1 克组织中最大浓度为 10 毫克的对比剂。还表明，即使组织中浓度低至 5 毫克/克，也能很好地保护危险器官免受剂量分布的影响。还对靶区中对比剂不均匀分布的存在的治疗策略进行了建模和讨论。
