Jaselskė Evelina, Adlienė Diana, Rudžianskas Viktoras, Urbonavičius Benas Gabrielis, Inčiūra Arturas
Physics Department of Kaunas University of Technology, Studentu str. 50, Kaunas, Lithuania.
Oncology Institute of Lithuanian University of Health Sciences, Eiveniu str. 2, Kaunas, Lithuania.
Phys Med. 2017 Dec;44:1-10. doi: 10.1016/j.ejmp.2017.11.003. Epub 2017 Nov 13.
In vivo dosimetry is a powerful tool for dose verification in radiotherapy. Its application in high dose rate (HDR) brachytherapy is usually limited to the estimation of gross errors, due to inability of the dosimetry system/ method to record non-uniform dose distribution in steep dose gradient fields close to the radioactive source. In vivo dose verification in interstitial catheter based HDR brachytherapy is crucial since the treatment is performed inserting radioactive source at the certain positions within the catheters that are pre-implanted into the tumour. We propose in vivo dose verification method for this type of brachytherapy treatment which is based on the comparison between experimentally measured and theoretical dose values calculated at well-defined locations corresponding dosemeter positions in the catheter. Dose measurements were performed using TLD 100-H rods (6 mm long, 1 mm diameter) inserted in a certain sequences into additionally pre-implanted dosimetry catheter. The adjustment of dosemeter positioning in the catheter was performed using reconstructed CT scans of patient with pre-implanted catheters. Doses to three Head&Neck and one Breast cancer patient have been measured during several randomly selected treatment fractions. It was found that the average experimental dose error varied from 4.02% to 12.93% during independent in vivo dosimetry control measurements for selected Head&Neck cancer patients and from 7.17% to 8.63% - for Breast cancer patient. Average experimental dose error was below the AAPM recommended margin of 20% and did not exceed the measurement uncertainty of 17.87% estimated for this type of dosemeters. Tendency of slightly increasing average dose error was observed in every following treatment fraction of the same patient. It was linked to the changes of theoretically estimated dosemeter positions due to the possible patient's organ movement between different treatment fractions, since catheter reconstruction was performed for the first treatment fraction only. These findings indicate potential for further average dose error reduction in catheter based brachytherapy by at least 2-3% in the case that catheter locations will be adjusted before each following treatment fraction, however it requires more detailed investigation.
体内剂量测定是放射治疗中剂量验证的有力工具。由于剂量测定系统/方法无法记录靠近放射源的陡峭剂量梯度场中的非均匀剂量分布，其在高剂量率（HDR）近距离放射治疗中的应用通常仅限于估计重大误差。基于间质导管的HDR近距离放射治疗中的体内剂量验证至关重要，因为该治疗是通过将放射源插入预先植入肿瘤的导管内的特定位置来进行的。我们提出了一种针对此类近距离放射治疗的体内剂量验证方法，该方法基于在与导管中剂量计位置相对应的明确位置处实验测量值与理论计算剂量值之间的比较。使用TLD 100-H棒（长6毫米，直径1毫米）以特定顺序插入额外预先植入的剂量测定导管中来进行剂量测量。使用预先植入导管的患者的重建CT扫描来进行剂量计在导管中的定位调整。在几个随机选择的治疗分次期间，对三名头颈癌患者和一名乳腺癌患者进行了剂量测量。结果发现，对于选定的头颈癌患者，在独立的体内剂量测定对照测量期间，平均实验剂量误差在4.02%至12.93%之间变化，对于乳腺癌患者，平均实验剂量误差在7.17%至8.63%之间变化。平均实验剂量误差低于美国医学物理学家协会（AAPM）推荐的20%的余量，并且未超过为此类剂量计估计的17.87%的测量不确定度。在同一患者的每个后续治疗分次中观察到平均剂量误差略有增加的趋势。这与由于不同治疗分次之间患者器官可能移动导致理论估计的剂量计位置变化有关，因为仅对第一个治疗分次进行了导管重建。这些发现表明，如果在每个后续治疗分次之前调整导管位置，基于导管的近距离放射治疗中进一步降低平均剂量误差至少2 - 3%具有潜力，然而这需要更详细的研究。
