Kato Takahiro, Sagara Tatsuhiko, Komori Shinya, Kato Ryohei, Takeuchi Akihiko, Narita Yuki
Preparing Section for New Faculty of Medical Science, Fukushima Medical University, Fukushima, Japan.
Department of Radiation Physics and Technology, Southern Tohoku Proton Therapy Center, Fukushima, Japan.
J Appl Clin Med Phys. 2021 Apr;22(4):158-165. doi: 10.1002/acm2.13222. Epub 2021 Mar 15.
This study aimed to evaluate the dosimetric properties of a newly developed thermoluminescent sheet-type dosimeter (TLD-sheet) for clinical proton beams.
The TLD-sheet is composed mainly of manganese doped lithium triborate, with a physical size and thickness of 150 mm × 150 mm and 0.15 mm respectively. It is flexible and can be cut freely for usage. The TLD-sheet has an effective atomic number of 7.3 and tissue-equivalent properties. We tested the reproducibility, fading effect, dose linearity, homogeneity, energy dependence, and water equivalent thickness (WET) of the TLD-sheet for clinical proton beams. We conducted tests with both unmodulated and modulated proton beams at energies of 150 and 210 MeV.
The measurement reproducibility was within 4%, which included the inhomogeneity of the TLD-sheet. The fading rates were approximately 20% and 30% after 2 and 7 days respectively. The TLD-sheet showed notable energy dependence in the Bragg peak and distal end of the spread-out Bragg peak regions. However, the dose-response characteristics of the TLD-sheet remained linear up to a physical dose of 10 Gy in this study. This linearity was highly superior to those of commonly used radiochromic film. The thin WET of the TLD-sheet had little effect on the range.
Although notable energy dependences were observed in Bragg peak region, the response characteristics examined in this study, such as reproducibility, fading effects, dose linearity, dose homogeneity and WET, showed that the TLD-sheet can be a useful and effective dosimetry tool. With its flexible and reusable characteristics, it may also be an excellent in vivo skin dosimetry tool for proton therapy.
本研究旨在评估一种新开发的用于临床质子束的热释光片型剂量计（TLD片）的剂量学特性。
TLD片主要由掺锰硼酸锂组成，物理尺寸和厚度分别为150 mm×150 mm和0.15 mm。它具有柔韧性，可自由裁剪使用。TLD片的有效原子序数为7.3，具有组织等效特性。我们测试了TLD片用于临床质子束的重复性、衰退效应、剂量线性、均匀性、能量依赖性和水等效厚度（WET）。我们在150和210 MeV能量下，对未调制和调制质子束都进行了测试。
测量重复性在4%以内，其中包括TLD片的不均匀性。2天和7天后的衰退率分别约为20%和30%。TLD片在布拉格峰和扩展布拉格峰区域的远端显示出显著的能量依赖性。然而，在本研究中，TLD片的剂量响应特性在物理剂量达到10 Gy之前仍保持线性。这种线性度远优于常用的放射变色胶片。TLD片的薄水等效厚度对射程影响很小。
尽管在布拉格峰区域观察到显著的能量依赖性，但本研究中所检测的响应特性，如重复性、衰退效应、剂量线性、剂量均匀性和水等效厚度，表明TLD片可以是一种有用且有效的剂量测定工具。凭借其灵活且可重复使用的特性，它也可能是质子治疗中一种出色的体内皮肤剂量测定工具。
