Department of Clinical Medicine, Aarhus University, Aarhus, Denmark.
Department of Clinical Medicine, Aarhus University, Aarhus, Denmark.
Brachytherapy. 2024 Sep-Oct;23(5):514-522. doi: 10.1016/j.brachy.2024.05.001. Epub 2024 Jun 8.
In vivo dosimetry (IVD) is rarely performed in brachytherapy (BT), allowing potential dose misadministration to go unnoticed. This study presents a clinical routine-calibration method of detectors for IVD in high (HDR) and pulsed dose rate (PDR) Ir-192 BT.
To evaluate the dosimetric precision and feasibility of an in-clinic calibration routine of detectors for IVD in afterloading BT.
Calibrations were performed in a PMMA phantom with two needles inserted 20 mm apart. The source was loaded in one of the needles at 15 dwells for 10 s. The detector was placed in the other needle, and its signal was recorded. The mean signal at each dwell position was fitted to the expected dose rate with the calibration factor and the detector's longitudinal position being free parameters. The method was tested with an inorganic scintillation detector using one Ir-192 FlexiSource HDR and two Ir-192 GammaMedPlus PDR sources and followed by validation measurements in water.
The standard measurement uncertainty (k = 1) of the calibration factor in absolute terms (Gy/s) was 3.2/3.4% for the HDR/PDR source. The uncertainty was dominated by source strength uncertainty, and the precision of the method was <1%. The mean ± 1SD of the difference in measured and expected dose rate during validation was 1.5 ± 4.7% (HDR) and 0.0 ± 4.1% (PDR) with a positional uncertainty in the setup of 0.33/0.23 mm (HDR/PDR) (k = 1).
A precise and feasible in-clinic calibration method for IVD and source strength consistency tests in BT was presented.
近距离放射治疗（BT）中很少进行体内剂量测定（IVD），这使得潜在的剂量误用无法被察觉。本研究提出了一种用于高剂量率（HDR）和脉冲剂量率（PDR）Ir-192 BT 后装近距离治疗中 IVD 的探测器临床常规校准方法。
评估在近距离治疗中对 IVD 进行探测器临床常规校准的剂量学精度和可行性。
在 PMMA 体模中进行校准，两个针相距 20mm 插入。源在一个针中加载 15 个驻留，每个驻留 10s。探测器放在另一个针中，记录其信号。每个驻留位置的平均信号与校准因子拟合，探测器的纵向位置为自由参数。该方法使用无机闪烁探测器对一个 Ir-192 FlexiSource HDR 和两个 Ir-192 GammaMedPlus PDR 源进行了测试，然后在水中进行了验证测量。
校准因子的标准测量不确定度（k=1）在绝对值（Gy/s）方面为 HDR/PDR 源的 3.2/3.4%。不确定性主要由源强度不确定性主导，该方法的精度<1%。验证期间测量和预期剂量率之间差异的平均值±1SD 为 1.5±4.7%（HDR）和 0.0±4.1%（PDR），在设置中位置不确定性为 0.33/0.23mm（HDR/PDR）（k=1）。
提出了一种精确且可行的用于 BT 中的 IVD 和源强度一致性测试的临床内校准方法。
