覆盖物对胸部肿瘤放射剂量影响的研究

Impact of the covering on radiotherapy dose for thoracic tumor patient

目的胸部肿瘤患者在放疗时,基于人性化治疗原则会给予覆盖物。本研究探讨覆盖物对胸部肿瘤放疗计量学的影响。方法选取上海交通大学胸科医院放疗科收治的10例胸部肿瘤患者,年龄57~68岁;包括局限期中上段食管癌7例(锁骨上淋巴结转移),胸腺瘤3例。比较测量和计算条件下不同大小射野模体不同深度处覆盖物对点剂量和面剂量影响,研究覆盖物对模体内剂量建成影响,评价覆盖物对10例胸部肿瘤治疗计划计算剂量影响。结果测量条件下,SAD=100cm,覆盖物使5cm×5cm、10cm×10cm和20cm×20cm射野固体水模体板表面下1cm处剂量分别增加2.5%、2.14%和1.61%;2、3、4、5和10cm深度处,覆盖物降低剂量约-0.18%^-0.47%。计算条件下,覆盖物对剂量影响与测量情况基本相当。覆盖物对模体表面到1.4cm深度TPS计算剂量有不同程度提升,1.5~1.6cm深度是覆盖物对组织剂量的平衡区,超过1.6cm深度剂量稍微降低。测量及计算条件下覆盖物降低模体2、3、4和5cm深度处平面各点剂量在-0.61%左右。覆盖物使PTV平均剂量和D95分别减小-0.77%(P<0.001)和-0.93%(P<0.001)。结论覆盖物对肿瘤患者体内剂量影响随深度而变化,特别对胸部肿瘤会造成靶区照射剂量偏差。

OBJECTIVE Thoracic cancer patient will be given covering while recieving human-based radiotherapy.This study explored the impact of the covering on radiotherapy dose for thoracic cancer patients.METHODS Ten thoracic cancer patients were recruited in this study treated in Radiotherapy Department of Shanghai Jiaotong University Shanghai Chest Hospital,ranged 57-68 years old,including local advanced middle and upper esophageal cancer 7cases（combined with collarbone lymph nodes metastasis）,thymoma 3cases.The impact on point dose and planar dose caused by the covering for different size fields at different depth in phantom between measured and calculated conditions were compared,the impact of the covering on build-up region dose was researched,and the impact of the covering on planning calculated dose for 10 thoracic cancer patients was evaluated.RESULTS Under measured conditions for SAD=100cm,5cm×5cm,10cm×10cm and 20cm×20cm fields,the covering increased phantom dose at depth 1cm by 2.5%,2.14% and 1.61%,respectively.At depth of 2cm,3cm,4cm,5cm and 10 cm,the covering decreased dose by about-0.18%to-0.47%.The covering impact on calculated dose matched with the measused.The covering increased calculated dose by different degrees from surface to 1.4cm depth in phantom,1.5-1.6cm was the dose balance region for the covering.Once deeper than 1.6cm in phantom,the dose decreased slightly.The covering decreased PTV Dmeanand D95by-0.77%（P〈0.001）and-0.93%（P〈0.001）,respectively.CONCLUSION The covering impact on dose changed with depth in patient,especially could cause dose coverage slightly less for thoracic tumor patient.