个体患者适形调强放疗计划模体内剂量实测验证技术的建立

目的建立个体患者适形调强放疗（IMRT）计划的模体内剂量实测验证技术。方法选择1例鼻咽癌患者，设计IMRT计划。将患者计划转移到模体上设计杂交计划。执行杂交计划时，用针点电离室测量感兴趣点的剂量，并与该点的计算剂量比较。用胶片剂量测量系统测量杂交计划中感兴趣平面的剂量，胶片与计划剂量矩阵登记后，依次进行计划，胶片分析、计划，胶片剖面分析和计划／胶片等剂量线分析。采用复合判断标准评价验证结果。结果针点电离室测量得到杂交计划单次照射的总剂量为121．5cGy，比计算值低约4％。计划，胶片分析得到高剂量、高梯度区域的距离差别均在4mm以内；计划／胶片剖面分析显示，计划与胶片在通过靶区的剖面具有较好的一致性；计划，胶片等剂量线分析显示，计划与胶片对应值的等剂量线重合良好。按照复合判断标准，该计划验证通过。结论初步建立了个体患者IMRT计划的模体内剂量实测验证技术，建立并优化了剂量登记技术、剂量归一方法和评价方法。

Establishment of dosimetric verification technique in phantom for intensity-modulated radiotherapy

Objective To develop the in-phantom dosimetric verification technique for intensity-modulated radiotherapy. Methods An IMRT plan for a NPC patient was designed and transferred to Med-Tech IMRT phantom to create a hybrid phantom plan. The dose at the point of interest was measured with the Pinpoint chamber and then compared with the calculated value. The film dosimeter including Kodak EDR2 film was used to measure planar dose distribution and the delivered dose distribution was compared with the planned one. The verification results were assessed by composite criterion. Results The measured point dose is 121.5 cGy, which is less than the computed mean dose by 4%. The distance from the region of high dose to that of high gradient is within 4 mm. A profile through the registered plan and film images showed a good agreement between the plan and the film. The superimposed isodose lines for the film image and the axial image from the hybrid plan overlaid well at each isodose level. The point dose in the high dose and low gradient region as well as the distance from the high dose to high gradient region agreed well in accordance with the corresponding criterion of accuracy. Conclusions The IMRT in-phantom dosimetric verification technique for individual patient has been established. The registration, normalization and evaluation of dose have been optimized.