Liu Chunbo, Zheng Dandan, Bradley Julie A, Vega Raymond B Mailhot, Li Zuofeng, Mendenhall Nancy P, Liang Xiaoying
Department of Radiation Oncology, University of Florida College of Medicine, Jacksonville, FL, USA; School of Physical Sciences, University of Science and Technology of China, Hefei, China.
Department of Radiation Oncology, University of Nebraska Medical Center, Omaha, NE, USA.
Phys Med. 2020 Sep;77:84-91. doi: 10.1016/j.ejmp.2020.08.006. Epub 2020 Aug 13.
To investigate, in proton therapy, whether the Gamma passing rate (GPR) is related to the patient dose error and whether MU scaling can improve dose accuracy.
Among 20 consecutively treated breast patients selected for analysis, two IMPT plans were retrospectively generated: (1) the pencil-beam (PB) plan and (2) the Monte Carlo (MC) plan. Patient-specific QA was performed. A 3%/3-mm Gamma analysis was conducted to compare the TPS-calculated PB algorithm dose distribution with the measured 2D dose. Dose errors were compared between the plans that passed the Gamma testing and those that failed. The MU was then scaled to obtain a better GPR. MU-scaled PB plan dose errors were compared to the original PB plan.
Of the 20 PB plans, 8 were passed Gamma testing (G_pass_group) and 12 failed (G_fail_group). Surprisingly, the G_pass_group had a greater dose error than the G_fail_group. The median (range) of the PTV DVH RMSE and PTV ΔDmean were 1.36 (1.00-1.91) Gy vs 1.18 (1.02-1.80) Gy and 1.23 (0.92-1.71) Gy vs 1.10 (0.87-1.49) Gy for the G_pass_group and the G_fail_group, respectively. MU scaling reduced overall dose error. However, for PTV D99 and D95, MU scaling worsened some cases.
For breast IMPT, the PB plans that passed the Gamma testing did not show smaller dose errors compared to the plans that failed. For individual plans, the MU scaling technique leads to overall smaller dose errors. However, we do not suggest use of the MU scaling technique to replace the MC plans when the MC algorithm is available.
在质子治疗中，研究伽马通过率（GPR）是否与患者剂量误差相关，以及监测单位（MU）缩放是否能提高剂量准确性。
在选取用于分析的20例连续接受治疗的乳腺癌患者中，回顾性生成了两个调强质子治疗（IMPT）计划：（1）笔形束（PB）计划和（2）蒙特卡罗（MC）计划。进行了患者特异性质量保证。进行3%/3毫米伽马分析，以比较治疗计划系统（TPS）计算的PB算法剂量分布与测量的二维剂量。比较通过伽马测试的计划和未通过的计划之间的剂量误差。然后对MU进行缩放以获得更好的GPR。将MU缩放后的PB计划剂量误差与原始PB计划进行比较。
在20个PB计划中，8个通过了伽马测试（G_pass组），12个未通过（G_fail组）。令人惊讶的是，G_pass组的剂量误差比G_fail组更大。G_pass组和G_fail组的计划靶体积（PTV）剂量体积直方图（DVH）的均方根误差（RMSE）中位数（范围）分别为1.36（1.00 - 1.91）Gy和1.18（1.02 - 1.80）Gy，PTV平均剂量差值（ΔDmean）分别为1.23（0.92 - 1.71）Gy和1.10（0.87 - 1.49）Gy。MU缩放降低了总体剂量误差。然而，对于PTV的D99和D95，MU缩放使一些病例的情况恶化。
对于乳腺癌IMPT，通过伽马测试的PB计划与未通过的计划相比，并未显示出更小的剂量误差。对于单个计划，MU缩放技术导致总体剂量误差更小。然而，当有MC算法可用时，我们不建议使用MU缩放技术来替代MC计划。
