Small-field dosimetry with detector-specific output correction factor for single-isocenter stereotactic radiotherapy of single and multiple brain metastases
Small-field dosimetry with detector-specific output correction factor for single-isocenter stereotactic radiotherapy of single and multiple brain metastases
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DOI：
10.1007/s12194-022-00684-0
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发表时间：
2022-10-22
影响因子：
1.6
通讯作者：
Mizowaki，Takashi
中科院分区：
文献类型：
--
作者：
Ono，Tomohiro;Kawata，Kohei;Mizowaki，Takashi
最近，国际原子能机构和美国医学物理学家协会报告了考虑到小场剂量测定中探测器读数的不确定性，探测器响应变化的校正因子（CF）。在这项研究中，评估了 CF 对脑转移瘤单等中心立体定向放射治疗的小视野剂量测量的影响。使用 TrueBeam（无平坦滤波器能量为 10 MV）在水当量球体模型中测量有和没有 CF 的输出因子 (OPF)。在垂直方向使用五个探测器：CC01、3D 精确电离室、非屏蔽 SFD 探测器、屏蔽 EDGE 探测器和 microDiamond 探测器。首先，使用多叶准直器 (MLC) 场将方形场尺寸设置为 5–100 毫米。在存在和不存在 CF 的情况下评估 OPF。其次，在动态适形弧 (DCA) 治疗后，对 15 名患者的 22 个脑转移瘤进行单等中心立体定向照射。使用每个规划目标体积的 MLC 孔径计算等效视野大小。对于 OPF，对于大于 10 mm 的方形视场尺寸，使用除 CC01 以外的探测器测量的剂量中位数的平均偏差在没有 CF 的中值的±±4.3% 以内，在有 CF 的中值的±±3.3% 以内。对于 DCA 计划，无 CF 和有 CF 的偏差分别为 CC01 的 − 2.3 ± 1.9% 和 − 4.8± 2.4%，3D 精确定位的 − 1.1± 3.0% 和 1.0 ± 1.6%，8.8 ± 3.0% 和SFD 为 2.9±±2.8%，EDGE 为 − 3.1±±3.0% 和 −13.5±±4.0%，microDiamond 为 8.9±±2.1% 和 0.8±±1.9%。该可行性研究证实，使用带有 CF 的适当探测器可以减少探测器的偏差。
Recently, the International Atomic Energy Agency and the American Association of Physicists in Medicine reported correction factors (CFs) for detector-response variation considering the uncertainty in detector readings in small-field dosimetry. In this study, the effect of CFs on small-field dosimetry measurements was evaluated for single-isocenter stereotactic radiotherapy for brain metastases. The output factors (OPFs) were measured with and without CFs in a water-equivalent sphere phantom using TrueBeam with a flattening-filter-free energy of 10 MV. Five detectors were used in a perpendicular orientation: CC01, 3D pinpoint ionization chambers, unshielded SFD detector, shielded EDGE detector, and microDiamond detector. First, the square-field sizes were set to 5–100 mm using a multi-leaf collimator (MLC) field. The OPFs were evaluated in the presence and absence of CFs. Second, single-isocenter stereotactic irradiation was performed on 22 brain metastases in 15 patients following dynamic conformal arc (DCA) treatment. The equivalent field size was calculated using the MLC aperture for each planning target volume. For the OPFs, the mean deviations from the median of the doses measured with detectors other than the CC01 for square-field sizes larger than 10 mm were within ± 4.3% of the median without CFs, and ± 3.3% with CFs. For DCA plans, the deviations without and with CFs were − 2.3 ± 1.9% and − 4.8 ± 2.4% for CC01, − 1.1 ± 3.0% and 1.0 ± 1.6% for 3D pinpoint, 8.8 ± 3.0% and 2.9 ± 2.8% for SFD, − 3.1 ± 3.0% and − 13.5 ± 4.0% for EDGE, and 8.9 ± 2.1% and 0.8 ± 1.9% for microDiamond. This feasibility study confirmed that the deviation of the detectors can be reduced using an appropriate detector with CFs.