School of Chemistry, Physics and Mechanical Engineering, Queensland University of Technology, Brisbane, Queensland, Australia.
Institute of Health & Biomedical Innovation, Queensland University of Technology, Brisbane, QLD, Australia.
PLoS One. 2019 Feb 28;14(2):e0213002. doi: 10.1371/journal.pone.0213002. eCollection 2019.
In prostate cancer treatment with external beam radiation therapy (EBRT), prostate motion and internal changes in tissue distribution can lead to a decrease in plan quality. In most currently used planning methods, the uncertainties due to prostate motion are compensated by irradiating a larger treatment volume. However, this could cause underdosage of the treatment volume and overdosage of the organs at risk (OARs). To reduce this problem, in this proof of principle study we developed and evaluated a novel adaptive planning method. The strategy proposed corrects the dose delivered by each beam according to the actual position of the target in order to produce a final dose distribution dosimetrically as similar as possible to the prescribed one.
Our adaptive planning method was tested on a phantom case and on a clinical case. For the first, a pilot study was performed on an in-silico pelvic phantom. A "library" of intensity modulated RT (IMRT) plans corresponding to possible positions of the prostate during a treatment fraction was generated at planning stage. Then a 3D random walk model was used to simulate possible displacements of the prostate during the treatment fraction. At treatment stage, at the end of each beam, based on the current position of the target, the beam from the library of plans, which could reproduce the best approximation of the prescribed dose distribution, was selected and delivered. In the clinical case, the same approach was used on two prostate cancer patients: for the first a tissue deformation was simulated in-silico and for the second a cone beam CT (CBCT) taken during the treatment was used to simulate an intra-fraction change. Then, dosimetric comparisons with the standard treatment plan and, for the second patient, also with an isocenter shift correction, were performed.
For the phantom case, the plan generated using the adaptive planning method was able to meet all the dosimetric requirements and to correct for a misdosage of 13% of the dose prescription on the prostate. For the first clinical case, the standard planning method caused underdosage of the seminal vesicles, respectively by 5% and 4% of the prescribed dose, when the position changes for the target were correctly taken into account. The proposed adaptive planning method corrected any possible missed target coverage, reducing at the same time the dose on the OARs. For the second clinical case, both with the standard planning strategy and with the isocenter shift correction target coverage was significantly worsened (in particular uniformity) and some organs exceeded some toxicity objectives. While with our approach, the most uniform coverage for the target was produced and systematically the lowest toxicity values for the organs at risk were achieved.
In our proof of principle study, the adaptive planning method performed better than the standard planning and the isocenter shift methods for prostate EBRT. It improved the coverage of the treatment volumes and lowered the dose to the OARs. This planning method is particularly promising for hypofractionated IMRT treatments in which a higher precision and control on dose deposition are needed. Further studies will be performed to test more extensively the proposed adaptive planning method and to evaluate it at a full clinical level.
在前列腺癌的外束放射治疗（EBRT）中，前列腺运动和组织分布的内部变化可能导致计划质量下降。在目前大多数使用的计划方法中，通过照射更大的治疗体积来补偿由于前列腺运动引起的不确定性。然而，这可能导致治疗体积的剂量不足和危及器官（OAR）的剂量过大。为了解决这个问题，在这项原理验证研究中，我们开发并评估了一种新的自适应计划方法。所提出的策略根据目标的实际位置校正每个射束的剂量，以便产生与规定剂量分布在剂量学上尽可能相似的最终剂量分布。
我们的自适应计划方法在体模病例和临床病例上进行了测试。对于第一个，在一个虚拟骨盆体模上进行了试点研究。在计划阶段生成了与前列腺在治疗分次期间可能位置相对应的强度调制放射治疗（IMRT）计划“库”。然后，使用三维随机游走模型模拟前列腺在治疗分次期间的可能位移。在治疗阶段，在每束结束时，根据目标的当前位置，从计划库中选择并输送能够再现规定剂量分布最佳逼近的射束。在临床病例中，对两名前列腺癌患者使用了相同的方法：对于第一个，在虚拟环境中模拟了组织变形；对于第二个，使用治疗期间拍摄的锥形束 CT（CBCT）模拟了分次内的变化。然后，与标准治疗计划进行了剂量比较，对于第二个患者，还与等中心移位校正进行了比较。
对于体模病例，使用自适应计划方法生成的计划能够满足所有剂量学要求，并纠正前列腺上 13%的剂量规定的剂量不足。对于第一个临床病例，当正确考虑到目标位置变化时，标准计划方法导致精囊分别出现 5%和 4%的剂量不足。所提出的自适应计划方法纠正了任何可能的靶区覆盖不足，同时降低了 OAR 上的剂量。对于第二个临床病例，无论是使用标准计划策略还是等中心移位校正，靶区覆盖率都明显恶化（特别是均匀性），并且一些器官超过了一些毒性目标。而通过我们的方法，为靶区提供了最均匀的覆盖，并始终为危及器官获得了最低的毒性值。
在我们的原理验证研究中，自适应计划方法在前列腺 EBRT 中优于标准计划和等中心移位方法。它提高了治疗体积的覆盖率，并降低了 OAR 上的剂量。这种计划方法对于需要更高精度和剂量沉积控制的短分割 IMRT 治疗特别有前途。将进一步进行研究，以更广泛地测试所提出的自适应计划方法，并在全临床水平上对其进行评估。
