Karlsson Leif, Thunberg Per, Johansson Bengt, Persliden Jan
Department of Medical Physics, Örebro University Hospital, Örebro, Sweden ; School of Health and Medical Sciences, Örebro University, Örebro, Sweden.
Department of Oncology, Örebro University Hospital, Örebro, Sweden.
J Contemp Brachytherapy. 2014 Oct;6(3):282-8. doi: 10.5114/jcb.2014.45586. Epub 2014 Sep 23.
Dose coverage is crucial for successful treatment in mono-brachytherapy. Since few and very high dose fractions are used, there is an important balance between dwell positioning outside the clinical target volume (CTV) and possible damage on adjacent normal tissue. The purpose of this study was to evaluate the possibility of having dwell positions close to the CTV surface, while maintaining an acceptable dose distribution, and to investigate the robustness in terms of known geometrical uncertainties of the implant.
This study included 37 patients who had received brachytherapy for prostate cancer as a monotherapy with the following schedules: 2 × 14 Gy or 3 × 11 Gy, each fraction separated by two weeks. The source dwell positions were activated 5 mm outside CTV. New optimizations were simulated for dwell positions at 3, 2, 1, and 0 mm. Inverse and graphical optimization were applied according to the relative dose constraints: V100 CTV ≥ 97%, Dmax, urethra ≤ 110%, and D10 rectal mucosa ≤ 65%. The V100, normal tissue outside CTV was used to evaluate dose variations caused by different dwell positions. Prostate geometries and dose distributions for the different dwell positions outside the CTV were used to investigate the impact on the CTV dose distribution due to geometrical uncertainties.
Both V100, CTV, and V100, normal tissue decreased, 98.6% to 92.2%, and 17 cm(3) to 9.0 cm(3), for dwell activation from 5 mm to 0 mm. The evaluation of both simulated longitudinal geometrical uncertainties and different source dwell activations implied that V100, CTV ranged from 98.6% to 86.3%.
It is possible to reduce the V100, normal tissue by decreasing the source dwell positions outside the CTV from 5 to 3 mm, while maintaining dose constraints. In combination with the estimated geometrical uncertainties, however, the source dwell positions need to be 5 mm from the surface in order to maintain a robust implant.
剂量覆盖对于单通道近距离放射治疗的成功治疗至关重要。由于使用的分次剂量少且剂量很高，临床靶区（CTV）外的驻留位置与相邻正常组织可能受到的损伤之间存在重要平衡。本研究的目的是评估在保持可接受剂量分布的同时，使驻留位置靠近CTV表面的可能性，并研究植入物已知几何不确定性方面的稳健性。
本研究纳入37例接受前列腺癌近距离放射治疗作为单一疗法的患者，治疗方案如下：2×14 Gy或3×11 Gy，每次分次间隔两周。源驻留位置在CTV外5 mm处激活。模拟了在3、2、1和0 mm处驻留位置的新优化。根据相对剂量约束应用逆向和图形优化：CTV的V100≥97%，尿道的Dmax≤110%，直肠黏膜的D10≤65%。CTV外正常组织的V100用于评估不同驻留位置引起的剂量变化。使用CTV外不同驻留位置的前列腺几何形状和剂量分布来研究几何不确定性对CTV剂量分布的影响。
驻留激活从5 mm降至0 mm时，CTV的V100和正常组织的V100均下降，分别从98.6%降至92.2%，以及从17 cm³降至9.0 cm³。对模拟的纵向几何不确定性和不同源驻留激活的评估表明，CTV的V100范围为98.6%至86.3%。
通过将CTV外的源驻留位置从5 mm减少到3 mm，可以减少正常组织的V100，同时保持剂量约束。然而，结合估计的几何不确定性，源驻留位置需要距离表面5 mm，以保持稳健的植入。
