Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas, USA.
J Appl Clin Med Phys. 2022 Jul;23(7):e13633. doi: 10.1002/acm2.13633. Epub 2022 May 9.
To better meet clinical needs and facilitate optimal treatment planning, we added two new electron energy beams (7 and 11 MeV) to two Varian TrueBeam linacs.
We worked with the vendor to create two additional customized electron energies without hardware modifications. For each beam, we set the bending magnet current and then optimized other beam-specific parameters to achieve depths of 50% ionization (I ) of 2.9 cm for 7 MeV and 4.2 cm for the 11 MeV beam with the 15 × 15 cm cone at 100 cm source-to-surface distance (SSD) by using an ionization chamber profiler (ICP) with a double-wedge (DW) phantom. Beams were steered and balanced to optimize symmetry with the ICP. After all parameters were set, full commissioning was done including measuring beam profiles, percent depth doses (PDDs), output factors (OFs) at standard, and extended SSDs. Measured data were compared between the two linacs and against the values calculated by our RayStation treatment planning system (TPS) following Medical Physics Practice Guideline 5.a (MPPG 5.a) guidelines.
The I values initially determined with the ICP/DW agreed with those from a PDD-scanned in-water phantom within 0.2 mm for the 7 and 11 MeV on both linacs. Comparison of the beam characteristics from the two linacs indicated that flatness and symmetry agreed within 0.4%, and point-by-point differences in PDD were within 0.01% ± 0.3% for the 7 MeV and 0.01% ± 0.3% for the 11 MeV. The OF ratios between the two linacs were 1.000 ± 0.007 for the 7 MeV and 1.004 ± 0.007 for the 11 MeV. Agreement between TPS-calculated outputs and measurements were -0.1% ± 1.0% for the 7 MeV and 0.2% ± 0.8% for the 11 MeV. All other parameters met the MPPG 5.a's 3%/3-mm criteria.
We were able to add two new beam energies with no hardware modifications. Tuning of the new beams was facilitated by the ICP/DW system allowing us to have the procedures done in a few hours and achieve highly consistent results across two linacs. PACS numbers: 87.55.Qr, 87.56.Fc.
为了更好地满足临床需求并促进最佳治疗计划，我们在两台瓦里安 TrueBeam 直线加速器上增加了两个新的电子能量束（7 和 11 MeV）。
我们与供应商合作，在不进行硬件修改的情况下创建了两个额外的定制电子能量。对于每个束，我们设定了弯曲磁铁电流，然后优化了其他束特定参数，以在 100 cm 源皮距（SSD）处使用带有双楔（DW）体模的电离室轮廓仪（ICP）实现 7 MeV 束的 50%电离深度（I）为 2.9 cm 和 11 MeV 束的 4.2 cm。使用 ICP 对束进行转向和平衡，以优化对称性。在设置完所有参数后，进行了全面调试，包括测量束流特性、百分深度剂量（PDD）、标准和扩展 SSD 下的输出因子（OF）。在两台直线加速器之间以及根据医学物理实践指南 5.a（MPPG 5.a）指南使用我们的 RayStation 治疗计划系统（TPS）计算的数值之间比较了测量数据。
在两台直线加速器上，使用 ICP/DW 最初确定的 I 值与 PDD 扫描水中体模的 I 值相差在 0.2mm 以内，误差在 0.2%以内。两台直线加速器的束特性比较表明，平坦度和对称性相差在 0.4%以内，PDD 的逐点差异在 7 MeV 时为 0.01%±0.3%，在 11 MeV 时为 0.01%±0.3%。两台直线加速器之间的 OF 比值为 7 MeV 时为 1.000±0.007，11 MeV 时为 1.004±0.007。TPS 计算输出与测量值之间的一致性为 7 MeV 时为-0.1%±1.0%，11 MeV 时为-0.2%±0.8%。所有其他参数均符合 MPPG 5.a 的 3%/3-mm 标准。
我们能够在不进行硬件修改的情况下添加两个新的束能量。新束的调谐得益于 ICP/DW 系统，使我们能够在几个小时内完成这些程序，并在两台直线加速器上获得高度一致的结果。
PACS 号：87.55.Qr，87.56.Fc。
