Muir Bryan R, Davis Thomas H, Dhanesar Sandeep, Hillman Yair, Iakovenko Viktor, Lei Yu, Pike Tina, Pinkham Daniel W, Vandervoort Eric, Kim Grace Gwe-Ya
Metrology Research Centre, National Research Council of Canada, Ottawa, Ontario, Canada.
Department of Radiation Oncology, University of Virginia, Charlottesville, Virginia, USA.
Med Phys. 2025 Jun;52(6):4971-4983. doi: 10.1002/mp.17802. Epub 2025 Apr 3.
The TG-51 protocol describes methods for obtaining reference dosimetry measurements for external photon and electron beams. Since the publication of TG-51 in 1999, research on reference dosimetry has allowed revisiting the procedures and data recommended in the protocol. An Addendum to TG-51 for electron beam reference dosimetry was published in 2024, which revises the formalism and procedures and provides updated data.
To compare clinical reference dosimetry measurements in electron beams obtained using the original American Association of Physicists in Medicine's (AAPM) TG-51 protocol and its associated Addendum (AAPM WGTG51 report 385).
Measurements were performed in electron beams using the data and methods prescribed by TG-51 and its Addendum. Nine participants (eight clinics and one primary standards laboratory) provided data and measurements. Results were obtained with 18 linacs using 87 total beam energies (4-6 energies per linac) between 4-22 MeV, representing the range of electron beam energies used clinically. Various cylindrical (6 types) and parallel-plate (4 types) ionization chamber types were employed, representing most of the chambers commonly used in modern radiation therapy clinics. An analysis was performed to determine if differences arise from the new data recommended for beam quality conversion factors or from changes to the procedure.
Results for dose to water per monitor unit obtained using the Addendum are up to 2.3% higher in low-energy beams and 1.3% higher in high-energy beams compared to results obtained using the original TG-51 protocol. These differences are consistent with what was predicted by the Addendum. Differences arise from both the changes to procedure (up to 0.7% from not requiring the correction for cylindrical chambers, 0.5% from the change in the shift of the point of measurement for parallel-plate chambers) as well as the recommended data (0.8% from differences in , 0.5% from differences in ).
This work elucidates where differences arise in results obtained using the original TG-51 protocol and its associated Addendum for electron beam reference dosimetry. The results presented here provide confidence in the new approach and data recommended by the Addendum. Clinical physicists can use these results to ensure that differences are as expected when implementing the Addendum.
TG - 51协议描述了获取外照射光子和电子束参考剂量测量的方法。自1999年TG - 51发布以来，参考剂量学研究使得重新审视该协议中推荐的程序和数据成为可能。2024年发布了TG - 51电子束参考剂量学增编，该增编修订了形式和程序，并提供了更新数据。
比较使用美国医学物理学家协会（AAPM）最初的TG - 51协议及其相关增编（AAPM WGTG51报告385）获得的电子束临床参考剂量测量结果。
使用TG - 51及其增编规定的数据和方法在电子束中进行测量。九名参与者（八个诊所和一个一级标准实验室）提供了数据和测量结果。使用18台直线加速器获得结果，总共有87种束能量（每台直线加速器4 - 6种能量），能量范围在4 - 22 MeV之间，代表了临床使用的电子束能量范围。采用了各种圆柱形（6种类型）和平行板（4种类型）电离室类型，代表了现代放射治疗诊所常用的大多数电离室。进行了一项分析，以确定差异是源于为束质转换因子推荐的新数据，还是源于程序的变化。
与使用原始TG - 51协议获得的结果相比，使用增编获得的每监测单位水吸收剂量结果在低能束中高出2.3%，在高能束中高出1.3%。这些差异与增编预测的结果一致。差异既源于程序的变化（圆柱形电离室不需要校正导致差异高达0.7%，平行板电离室测量点偏移的变化导致差异0.5%），也源于推荐的数据（ 差异导致0.8%， 差异导致0.5%）。
这项工作阐明了使用原始TG - 51协议及其相关电子束参考剂量学增编获得的结果中差异产生的位置。这里呈现的结果为增编推荐的新方法和数据提供了信心。临床物理学家可以使用这些结果来确保在实施增编时差异符合预期。
