Monaco计划系统中构建治疗床模型对放疗剂量控制意义探讨  

Significance of modeling the treatment couch in the Monaco treatment planning system for dose control of radiotherapy

作　　者：张若辉 白文文[1] 樊晓妹[1] 曹彦坤[1] 邱嵘[1] 迟子锋[1] 韩春[1] 

机构地区：[1]河北医科大学第四医院放射治疗科,河北石家庄050011

出　　处：《中华肿瘤防治杂志》2016年第2期105-109,共5页Chinese Journal of Cancer Prevention and Treatment

摘　　要：目的 Monaco计划系统采用蒙卡算法提高了剂量运算精确性,但忽略了治疗床对放疗剂量的影响。本研究量化Elekta Synergy直线加速器iBEAM○Revo Couchtop EP治疗床对剂量吸收的影响,在Monaco计划系统中模拟构建治疗床模型以降低治疗床对放疗剂量的影响。方法将圆柱型均匀模体分别放置在治疗床的左、中、右3个位置,机架从180°到射野与治疗床相互作用的边缘,每间隔10°测量其衰减系数。将电离室放置在模体等中心,采用6 MV光子线在10cm×10cm射野下进行测量。以实际测量治疗床衰减值为参考值,通过不断调整相对电子密度值确定治疗床模型电子密度值。通过最小计算网格(2mm)模拟结果评估治疗床模型构建的精确性。结果在Monaco计划系统中治疗床模型外层碳纤维采用0.5g/cm3和内层碳泡沫采用0.1g/cm3,对于6 MV光子线不同机架角度计算值和测量值有很好的一致性。除了当模体位于治疗床左侧机架为140°时相对偏差可达1.79%外,其他值均<0.94%。不引入治疗床模型,模体位于治疗床左、中、右位置时,实际测量和计算的剂量偏差最大分别可达5.52%、4.74%和4.54%;当引入治疗床模型后,测量和计算平均绝对剂量差由不包含治疗床模型的4.42%、4.2%和3.51%,分别减少到0.63%、0.3%和0.42%。结论 Monaco计划系统中构建iBEAM○Revo Couchtop治疗床模型可以精确的模拟治疗床对剂量的衰减,在计划设计时可以采用。OBJECTIVE The use of Monte Carlo treatment planning systems（TPS）in radiation therapy has increased the dosimetric accuracy of VMAT treatment sequences.However,this accuracy is compromised by not including the treatment couch into the treatment planning process.Therefore,the impact of the treatment couch on radiation delivery output was determined,and a couch model was included and tested in the Monaco TPS to minimize the impact of radiation dose of the treatment couch.METHODS The attenuation characteristics of an iBEAM○Revo Couchtop EP was evaluated for three different phantom positions（on the left half,in the center and on the right half of the couch）in A-B direction,for 6 MV energy at the field size of 10 by 10square centimetre.Dose measurements of couch attenuation were performed from the gantry angle of 180°to the gantry angle which penetrates the couch edge and with the increment of 10°,using a 0.125 cc semiflex ionization chamber,isocentrically placed in the center of a homogeneous cylindric sliced RW3 phantom.Each experimental setup was first measured on the linear accelerator and then reproduced in the TPS.By adjusting the relative to water electron density values of the couch compents,the measured attenuation was replicated.The simulated results were evaluated by comparing the measurements and simulations results at the minimizing the computational grid（2mm）.RESULTS Using couch fiber density of 0.5g/cm3 and foam density of 0.1g/cm3,the resluts demonstrated an excellent agreement between measured dose and Monaco TPS computed dose for 6 MV beam.The relative deviation was within 0.94% for all gantry angle measured except for the phantom is positioned on the left side of the treatment couch at the gantry angle of 140°,which was 1.79%.Without the couch model inclued,the maximum measured and calcaulted percentage deviation for the phantom at left,central and right positions were 5.52%,4.74% and4.54%.After including the treatment couch,the mean absolute dose difference was reduced from（4.42%,

关 键 词：放射治疗 治疗床 治疗计划系统 剂量学 剂量衰减 

分 类 号：R730.55[医药卫生—肿瘤]