Khosravi H, Hashemi B, Mahdavi S R, Hejazi P
Ph.D. Candidate, Department of Medical Physics, Tarbiat Modares University, Tehran, Iran;
Associate Professor, Department of Medical Physics, Tarbiat Modares University, Tehran, Iran;
J Biomed Phys Eng. 2015 Mar 4;5(1):3-14. eCollection 2015 Mar.
Gel polymers are considered as new dosimeters for determining radiotherapy dose distribution in three dimensions.
The ability of a new formulation of MAGIC-f polymer gel was assessed by experimental measurement and Monte Carlo (MC) method for studying the effect of gold nanoparticles (GNPs) in prostate dose distributions under the internal Ir-192 and external 18MV radiotherapy practices.
A Plexiglas phantom was made representing human pelvis. The GNP shaving 15 nm in diameter and 0.1 mM concentration were synthesized using chemical reduction method. Then, a new formulation of MAGIC-f gel was synthesized. The fabricated gel was poured in the tubes located at the prostate (with and without the GNPs) and bladder locations of the phantom. The phantom was irradiated to an Ir-192 source and 18 MV beam of a Varian linac separately based on common radiotherapy procedures used for prostate cancer. After 24 hours, the irradiated gels were read using a Siemens 1.5 Tesla MRI scanner. The absolute doses at the reference points and isodose curves resulted from the experimental measurement of the gels and MC simulations following the internal and external radiotherapy practices were compared.
The mean absorbed doses measured with the gel in the presence of the GNPs in prostate were 15% and 8 % higher than the corresponding values without the GNPs under the internal and external radiation therapies, respectively. MC simulations also indicated a dose increase of 14 % and 7 % due to presence of the GNPs, for the same experimental internal and external radiotherapy practices, respectively.
There was a good agreement between the dose enhancement factors (DEFs) estimated with MC simulations and experiment gel measurements due to the GNPs. The results indicated that the polymer gel dosimetry method as developed and used in this study, can be recommended as a reliable method for investigating the DEF of GNPs in internal and external radiotherapy practices.
凝胶聚合物被视为用于确定三维放射治疗剂量分布的新型剂量计。
通过实验测量和蒙特卡罗（MC）方法评估新型MAGIC-f聚合物凝胶制剂，以研究金纳米颗粒（GNPs）在Ir-192内照射和18MV外照射放疗实践下对前列腺剂量分布的影响。
制作一个代表人体骨盆的有机玻璃模型。采用化学还原法合成直径为15nm、浓度为0.1mM的金纳米颗粒。然后，合成新型MAGIC-f凝胶制剂。将制备好的凝胶分别倒入位于模型前列腺（含和不含金纳米颗粒）和膀胱位置的试管中。根据用于前列腺癌的常规放疗程序，将模型分别照射到Ir-192源和Varian直线加速器的18MV射束上。24小时后，使用西门子1.5特斯拉磁共振成像扫描仪读取照射后的凝胶。比较凝胶实验测量和内、外放疗实践后的MC模拟得出的参考点绝对剂量和等剂量曲线。
在内照射和外照射放疗下，前列腺中存在金纳米颗粒时凝胶测量的平均吸收剂量分别比不存在金纳米颗粒时的相应值高15%和8%。MC模拟也表明，对于相同的实验内、外放疗实践，由于金纳米颗粒的存在，剂量分别增加了14%和7%。
MC模拟估计的和实验凝胶测量得到的由于金纳米颗粒导致的剂量增强因子（DEFs）之间有良好的一致性。结果表明，本研究开发和使用的聚合物凝胶剂量测定方法可推荐为研究金纳米颗粒在内外放疗实践中DEF的可靠方法。
