用二维电离室阵列对螺旋断层治疗的调强计划进行剂量验证

Two-dimensional ion chamber array in dose verification for intensity modulated planning of helical tomotherapy

目的研究采用二维电离室阵列对螺旋断层治疗（HT）的调强计划实施剂量验证的可行性，寻求建立一套临床上针对该条件下患者治疗更为有效的剂量验证方法。方法采用IBA公司I’mRT MatriXX二维电离室阵列及其相配套MULTICube等效固体水模体对10例患者HT的调强计划实施验证。分别对二维电离室阵列实行冠状及纵向位测量，并获取模体中阵列轴平面和纵断面剂量分布。通过HT系统兆伏级CT图像实现模体精确配准及校正，以确保二维电离室阵列摆位准确性。束流照射后将二维阵列剂量测量平面分布与HT计划系统模体计划中计算平面结果进行比较，定性或定量分析其绝对剂量及相对剂量验证情况。探讨其不同位置摆放来实现其测量方法的可行性。结果定性或定量分析所测量与计算绝对剂量点及相对剂量分布的结果均显示出了较好一致性，点绝对测量与计算剂量偏差保持在±3％以内。MatriXX阵列测量的相对剂量分布与治疗计划系统模体中计算平面相比较，采用了Gamma法（3mm或3％）进行2mm栅格精度分析，1≤1像素点平均通过率分别为97．76％、96．83％。结论MatriXX二维电离室阵列可较好地进行绝对剂量及相对剂量测量，能较好地实现调强计划的剂量验证。

Objective To investigate the feasibility of dose verification of intensity modulated （IM） planning of helical tomotherapy （HT） using two-dimensional ion chamber array （2DICA）, and develop an efficient way to validate the dose delivered under the parameters mirroring those during the treatment. Methods A 2DICA,I＇mRT MatriXX and MULTICube equivalent solid water phantom from IBA company were used to verify the dose distribution of 10 IM planning. The combined phantom was set up to measure the dose distributions on coronal and sagittal surface. The precise setup of phantom was guided by HTMVCT images. After the irradiation, the measured dose distributions on the coronal and sagittal plane were compared with those calculated by the IM planning system for verification. The results were evaluated and the feasibility of the different measuring methods was studied. Results The dose distribution measured by the MatriXX 2DICA was well consistent with that calculated by the treatment planning system. The errors between the measured dose and predicted dose in the selected points were within ± 3%. In the comparison of the pixelsegmented ionization chamber versus treatment planning system using the 3 mm/3% γ criteria, the passing ratio of pixels with γ parameter ≤1 was 97.76% and 96.83% ,respectively. Conclusions MatriXX is able to measure the absolute and relative dose distributions simultaneously, which can be used for dose verification of IM planning.