Sensitivity of a helical diode array device to delivery errors in IMRT treatment and establishment of tolerance level for pretreatment QA.
Sensitivity of a helical diode array device to delivery errors in IMRT treatment and establishment of tolerance level for pretreatment QA.
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DOI：
10.1120/jacmp.v13i1.3660
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发表时间：
2012-01-05
影响因子：
2.1
通讯作者：
Torres JJ
中科院分区：
文献类型：
--
作者：
García-Vicente F;Fernández V;Bermúdez R;Gómez A;Pérez L;Zapatero A;Torres JJ
本研究的目的是确定插入微电离室的二极管螺旋阵列的门架角度和多叶准直器(MLC)间隙错误检测阈值，以便将该设备用于调强放射治疗(IMRT)的前处理质量保证(QA)。还将考虑对患者治疗的剂量-体积直方图(DVH)的影响，以建立具有合理耐受水平的质量保证方案。对三种动态调强放射治疗HN(头颈部)和前列腺治疗进行了研究。分析临床治疗中门架角度的随机和系统变化以及MLC间隙宽度的系统误差，以确定该阵列的检测灵敏度。研究了相关的临床意义，在基于患者CT的治疗计划中引入相同的误差，并计算相应的DVH。对于旋转误差为1°的两种治疗方式，Gamma(3%/3 mm)的失败率变化为4%。门架旋转角度的系统误差和随机误差对患者的DVH影响不大。在前列腺治疗中，MLC间隙宽度误差为1 mm和2 mm，意味着等中心测量的吸收剂量的平均偏差分别为2.1%和4.1%。在HN的情况下，这些误差导致测量的等中心剂量分别变化4.7%和8.6%。在患者的DVH中观察到的变化基本上是曲线的整体位移，与由间隙宽度误差引起的等中心剂量变化成正比。根据阵列对分析误差的敏感性及其在患者DVH中的意义，我们将伽玛标准3%/2 mm的95%点通过率的容差和2%的等中心绝对剂量一致性作为我们的前IMRT QA方案的容差标准。PAC编号：87.56.Fc
The aim of this study is to determine the gantry angle and multileaf collimator (MLC) gap error‐detection threshold of a diode helical array with an inserted microionization chamber in order to use this device for the pretreatment quality assurance (QA) of intensity‐modulated radiation therapy (IMRT) treatments. Implications on the dose‐volume histograms (DVHs) of the patient treatments will also be considered for the establishment of a QA protocol with a reasonable tolerance level. Three dynamic IMRT HN (head and neck) and prostate treatments were studied. Random and systematic variations of gantry angle and systematic errors in MLC gap width of the clinical treatments were analyzed in order to establish the detection sensitivity of the array. The associated clinical significance was studied introducing the same errors in the treatment plan based on the patients' computed tomography (CT) and calculating the corresponding DVHs. The Gamma (3%/3 mm) presented a 4% variation in failure rate for a rotation error of 1° for both types of treatment. Both systematic and random errors in gantry rotation angle have little effect on the patients' DVHs. MLC gap width errors of 1 mm and 2 mm in the prostate treatments imply a mean variation in isocenter‐measured absorbed dose of 2.1% and 4.1%, respectively. In the case of HN, these errors entail a change in measured isocenter dose of 4.7% and 8.6%, respectively. The variation observed in the DVHs of the patients was, basically, a global displacement of the curves proportional to the isocenter dose variation caused by the gap width error. According to the array sensitivity to the analyzed errors and its implication in patient DVHs, a tolerance of 95% point passing rate for the gamma criterion 3%/2 mm and an agreement of 2% in isocenter absolute dose have been established as tolerance criteria for our pretreatment IMRT QA protocol. PACS number: 87.56.Fc
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