Mason Josh, Al-Qaisieh Bashar, Bownes Peter, Henry Ann, Thwaites David
Department of Medical Physics and Engineering, St. James's Institute of Oncology, St. James's University Hospital, Leeds, UK; Academic Unit of Medical Physics, University of Leeds, Leeds, UK.
Department of Medical Physics and Engineering, St. James's Institute of Oncology, St. James's University Hospital, Leeds, UK.
Brachytherapy. 2014 Nov-Dec;13(6):603-10. doi: 10.1016/j.brachy.2014.04.004. Epub 2014 Jun 7.
To use Monte Carlo (MC) simulation and sector analysis to assess interseed attenuation and scatter (ISA) and tissue effects in permanent seed implant prostate brachytherapy and to compare methods for modeling tissue.
CT-based postimplant plan simulations for 40 patients were evaluated using dose-volume histogram (DVH) parameters and sector analysis. Simulations in water (to evaluate ISA alone) and tissue assigned from contours or CT data, with and without calcifications, were compared.
For patients without calcifications, mean combined ISA and tissue effect reduced prostate D90 by 4.2 Gy (2.9%), prostate V100 by 0.5 cm(3) (1.4%), urethra D10 by 8.6 Gy (3.5%), rectal [Formula: see text] by 11.6 Gy (10.5%), and the 100% isodose volume by 4.7 cm(3). Larger differences were observed comparing planned dose to postimplant, mean prostate D90 reduced from 185 to 149.8 Gy (-19%). For patients with calcifications, larger tissue effects were observed, prostate D90 reduced by up to 7.4%. Sector analysis showed dose reductions were larger in anterior and base sectors of the prostate. For patients without calcifications, contour- and CT-based tissue model results agreed within <0.5% for all DVH parameters, with up to 4% difference for patients with calcifications.
Advanced brachytherapy dose calculation methods that take account of ISA and tissue effects show that clinical (125)I implant dose is different from TG-43U1 (AAPM Task Group No. 43 Report-Update 1) calculations, reducing DVH parameter values particularly for patients with calcifications. Peripheral dose and areas of the implant with relatively poorer coverage are particularly affected. However, dose reductions are small compared with other postimplant dose uncertainties.
运用蒙特卡罗（MC）模拟和扇形分析评估永久性籽源植入前列腺近距离放射治疗中的籽源间衰减和散射（ISA）以及组织效应，并比较组织建模方法。
使用剂量体积直方图（DVH）参数和扇形分析对40例患者基于CT的植入后计划模拟进行评估。比较了在水中（仅评估ISA）以及根据轮廓或CT数据分配的组织（有或无钙化）中的模拟情况。
对于无钙化的患者，ISA和组织效应的综合作用使前列腺D90降低4.2 Gy（2.9%），前列腺V100降低0.5 cm³（1.4%），尿道D10降低8.6 Gy（3.5%），直肠Dmean降低11.6 Gy（10.5%），100%等剂量体积降低4.7 cm³。将计划剂量与植入后剂量比较时观察到更大差异，前列腺平均D90从185 Gy降至149.8 Gy（-19%）。对于有钙化的患者，观察到更大的组织效应，前列腺D90降低高达7.4%。扇形分析显示前列腺前部和底部扇形区域的剂量降低更大。对于无钙化的患者，基于轮廓和基于CT的组织模型结果在所有DVH参数上的差异<0.5%，对于有钙化的患者差异高达4%。
考虑ISA和组织效应的先进近距离放射治疗剂量计算方法表明，临床¹²⁵I植入剂量与TG - 43U1（美国医学物理学会第43任务组报告 - 更新1）计算结果不同，尤其对于有钙化的患者会降低DVH参数值。周边剂量和植入物覆盖相对较差的区域受到的影响尤为明显。然而，与其他植入后剂量不确定性相比，剂量降低幅度较小。
