碳纤维治疗床在Monaco中的建模及剂量学影响

Modeling and dosimetric effect of carbon fiber couch in Monaco

目的研究放疗中碳纤维治疗床对患者剂量分布的影响。方法测量射野点剂量得到碳纤维治疗床对射线的衰减,并依此在计划系统Monaco中进行治疗床的建模。选择2019年5月至12月于复旦大学附属中山医院接受放疗的5例鼻咽癌、5例直肠癌和5例椎体转移患者,在放疗计划系统Monaco中分析添加治疗床前后患者剂量分布的变化,并对这15例的剂量验证结果进行比较分析。结果通过比较Monaco计算与实测的治疗床衰减确定Monaco中的治疗床模型。添加该模型后,鼻咽癌、直肠癌和椎体转移病例的Gamma3mm/3%验证通过率平均增加0.32%、0.26%和2.06%。治疗床对靶区剂量影响最大的是椎体转移,衰减最大处达处方量的5%左右;其次是直肠癌,少量点达4%左右;对鼻咽癌的影响最小,衰减基本在3%之内。射线穿过治疗床可引起皮肤剂量的增加,对鼻咽癌,皮肤剂量增加最大约为处方量的8%;对部分直肠癌和椎体转移病例,皮肤剂量增加高达16%。结论治疗床会引起靶区剂量的减少和皮肤剂量的增加。

Objective To study the dose effect of carbon fiber couch on target and skin in radiotherapy.Methods The dose attenuation of the carbon fiber couch was obtained by measuring point dose of the beam fields.Then the couch was modeled in Monaco.Five patients with nasopharyngeal cancer,5 patients with rectal cancer and 5 patients with vertebral metastasis who received radiotherapy at Zhongshan Hospital Affiliated to Fudan University from May to December 2019 were selected to analyze the changes of dose distribution before and after the addition of couch in Monaco Planning System,and the dose verification results of these 15 patients were compared and analyzed.Results The model of couch was established by comparing the Monaco calculation with the measured couch attenuation.The addition of this model increased the Gamma 3 mm/3%verification pass rates by 0.32%,0.26%and 2.06%,on average,in patients with nasopharyngeal cancer,rectal cancer,and vertebral metastasis.The largest attenuation of the couch on the target dose was observed in cases of vertebral metastasis,which were about 5%of the prescription.The second was in cases of rectal cancer,a small number of about 4%of the prescription.The couch had the smallest impact on cases of nasopharyngeal cancer,with the attenuation basically within 3%of the prescription.The couch could also cause an increase on the skin dose,up to about 8%of the prescribed dose for cases of nasopharyngeal cancer,while for cases of rectal cancer and vertebral metastasis,the skin dose increase was as high as 16%of the prescription.Conclusions The couch can decrease the target dose and increase the skin dose.