协和医学杂志

2013, (04)

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应用二维电离室矩阵对后装剂量分布的验证
Research on the use of two-dimensional ionization chamber array on brachytherapy dose verification

于浪;杨波;庞廷田;李文博;刘建纯;邱杰;张福泉

摘要(Abstract):

[摘要] 目的:探讨二维电离室矩阵系统Matrixx envlution对近距离治疗剂量分布进行验证的可行性,寻求建立一套切实可行的近距离治疗剂量分布的验证方法。方法:利用井型电离室校准放射源Ir192的活度,再使用该放射源通过Valencia皮肤施源器、SP34等效固体水模,完成对GafChromic EBT3胶片的刻度,获取剂量灰度曲线,找到经过Valencia皮肤施源器均整后的Ir192辐射野中轴的百分深度剂量曲线后即可进行对德国IBA公司的Matrixx envlution二维电离室矩阵进行刻度,得到剂量刻度因子Kuser。采用Freiburg Flap 施源器和插植针及固体水建立模体,获取CT图像,在计划系统(TPS)内完成管道重建以及剂量分布计算,传输至nucletron 后装机(Nucletron, Veenendaal, The Netherlands)执行计划,通过matrix envlution 获取特定冠状层面内的剂量分布与计划系统所得剂量分布进行比较,利用OmniPro-I‘mRT软件分析测量与计划剂量分布结果。结果:经valencia皮肤施源器均整后的Ir192辐射场的剂量分布类似加速器的射野,横向及纵向对称性分别为0.17%和0.16%,PDD最大剂量点位于施源器表面下3mm处,施源器表面下1.16cm处的PDD=46.5%。经该辐射场刻度的Matrixx envlution阵列测量的剂量分布与治疗计划系统模体中计算平面相比较,采用γ分析方法法(3mm或3%)进行1 mm栅格精度分析,γ≤1的剂量点所占比例为97.67%,点绝对剂量测量与TPS剂量偏差保持在士5%以内。结论:使用带有均整器的valencia施源器可以对放射源的辐射场进行修整,修整后的均匀辐射场便于剂量计算和测量,可直接用于验证工具的刻度,避免了近源处高剂量梯度时由于位置误差造成的剂量误差;同源刻度,极大减少了验证工具的能量响应问题。Matrixx envlution作为近距离治疗剂量分布的验证工具具有重复性好,避免了使用胶片验证的成本损耗,是目前较为快速 、便捷的近距离治疗剂量学验证的QA工具。
[Abstract] Objective: To investigate the two-dimensional ionization chamber array Matrixx’s feasibility of brachytherapy plan verification, seeking to establish a set of feasible brachytherapy dose distribution verification method. Methods: using well-type chamber to verify the source activity of Ir192 ; using the radioactive source to complete the calibration of GafChromic film model EBT3 through the Valencia skin applicator and SP34 water equivalent solid phantom,gets dose gray curve, find the percentage depth dose(PDD) curves under Valencia skin applicator and use it to help calibrating the Germany IBA company's two-dimensional ionization chamber array Matrixx, get a calibration factor Kuser. Using Freiburg Flap applicator and inserting the needle combine with solid water to build a phantom, after CT scans, complete the catheter reconstruction and dose distribution calibration in the oncentra treatment planning system, using the measurement and analysis software of OmniPro I’mRT,the planned dose distribution and measurement dose distributions were compared. Results: the Ir192 dose distribution under Valencia skin applicator is of similar to accelerator beam, transverse and longitudinal symmetry is 0.17% and 0.16% respectively, the PDD of maximum dose is at 3mm under the applicator surface, PDD46.5% is at 11.6mm under the applicator surface. The measured dose distribution and TPS calculated dose plane is compared, using gamma analysis method (3mm/3%) with 1 mm grid, the ratio of pixels withinγ ≤ 1 is 97.67%, absolute dose measurement and calculation of dose deviation remains in 5%. Conclusion: the use of radiation field with a flattening filter Valencia applicator can be a source of radiation for trimming, trimmed uniform radiation field for dose calculation and measurement, can be directly used for calibration verification tool, to avoid the high dose gradient near the source due to dose error caused by position error, greatly reduced the energy response of the verification tool. Matrixx envlution as brachytherapy dose distribution verification tool has good repeatability, avoiding the cost loss using film validation, is more rapid, convenient one of brachytherapy dosimetry QA verification tool.

关键词(KeyWords): |施源器|近距离计划验证|后装剂量分布|二维电离室矩阵|胶片剂量仪|
|applicator| brachytherapy plan verification| brachytherapy dose distribution| two-dimensional ionization chamber array| Film EBT3 dosimeter|

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作者(Author): 于浪;杨波;庞廷田;李文博;刘建纯;邱杰;张福泉

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