混合电子-光子束放疗（MBRT）是一种新兴技术，其中外部电子和光子束同时优化为单一的治疗计划。MBRT利用电子的剂量迅速下降和高表面剂量，同时通过利用光子的陡峭半影保持靶区的一致性。本研究旨在研究MBRT对软组织肉瘤（STS）患者的剂量学益处。以传统基于光子的容积调制弧疗法（VMAT）治疗的下肢STS 22例回顾性队列被重新计划为MBRT。Varian TrueBeam线性加速器上的VMAT和MBRT治疗均采用Millenium多叶片准直器进行计划。MBRT计划的电子束未使用电子隔离器、切开或其他共轭性分鬆装置。MBRT计划通过鲁棒列生成算法优化，使用6 MV光子和五种电子能量（6、9、12、16、20 MeV）的组合。本研究中的电子束以标准的100 cm源轴距（SAD）进行计划。使用Wilcoxon符号秩检验比较临床靶区容积（CTV）、骨骼、正常组织带和其他危及器官（OAR）的剂量。在原始VMAT治疗中，10例患者需要组织等效块。由于较高的电子进入剂量，MBRT计划不需要块。处方剂量下CTV的覆盖在两种治疗方式的计划中被认为是临床等效的：V 50Gy (MBRT) = 97.9 ± 0.2%，V 50Gy (VMAT) = 98.1 ± 0.6% (p=0.34)。通过比较MBRT和VMAT计划中OAR的剂量差异的绝对配对差异，我们观察到MBRT计划中的正常组织V 20Gy比VMAT计划降低了14.9 ± 3.2% (p < 10 - 6) $p<10^{-6}$ 。类似地，MBRT计划中的骨骼V 50Gy相对于骨骼体积减少了8.2 ± 4.0% (p < 10 - 3) $p<10^{-3}$ 。对于皮下侵犯的STS，与VMAT相比，MBRT可以在不损害靶区覆盖的情况下，显著减少OAR的剂量。MBRT计划可以在常规线性加速器上实施，而无需使用电子隔离器、缩短源到表面距离（SSD）或块。本研究表明，MBRT是一种具有明显剂量学益处的可行技术。© 2023 The Authors. Medical Physics published by Wiley Periodicals LLC on behalf of American Association of Physicists in Medicine.

Mixed electron-photon beam radiation therapy (MBRT) is an emerging technique in which external electron and photon beams are simultaneously optimized into a single treatment plan. MBRT exploits the steep dose falloff and high surface dose of electrons while maintaining target conformity by leveraging the sharp penumbra of photons.This study investigates the dosimetric benefits of MBRT for soft tissue sarcoma (STS) patients.A retrospective cohort of 22 STS of the lower extremity treated with conventional photon-based Volumetric Modulated Arc Therapy (VMAT) were replanned with MBRT. Both VMAT and MBRT treatments were planned on the Varian TrueBeam linac using the Millenium multi-leaf collimator. No electron applicator, cutout or additional collimating devices were used for electron beams of MBRT plans. MBRT plans were optimized to use a combination of 6 MV photons and five electron energies (6, 9, 12, 16, 20 MeV) by a robust column generation algorithm. Electron beams in this study were planned at standard 100 cm source-axis distance (SAD). The dose to the clinical target volume (CTV), bone, normal tissue strip and other organs-at-risk (OARs) were compared using a Wilcoxon signed-rank test.As part of the original VMAT treatment, tissue-equivalent bolus was required in 10 of the 22 patients. MBRT plans did not require bolus by virtue of the higher electron entrance dose. CTV coverage by the prescription dose was found to be clinically equivalent between plans of either modality: V 50Gy $V_{\text{50Gy}}$ (MBRT) = 97.9 ± 0.2% versus V 50Gy $V_{\text{50Gy}}$ (VMAT) = 98.1 ± 0.6% (p=0.34). Evaluating the absolute paired difference between doses to OARs in MBRT and VMAT plans, we observed lower V 20Gy $V_{\text{20Gy}}$ to normal tissue in MBRT plans by 14.9 ± 3.2% ( p < 10 - 6 $p<10^{-6}$ ). Similarly, V 50Gy $V_{\text{50Gy}}$ to bone was found to be decreased by 8.2 ± 4.0% ( p < 10 - 3 $p<10^{-3}$ ) of the bone volume.For STS with subcutaneous involvement, MBRT offers statistically significant sparing of OARs without sacrificing target coverage when compared to VMAT. MBRT plans are deliverable on conventional linacs without the use of electron applicators, shortened source-to-surface distance (SSD) or bolus. This study shows that MBRT is a logistically feasible technique with clear dosimetric benefits.© 2023 The Authors. Medical Physics published by Wiley Periodicals LLC on behalf of American Association of Physicists in Medicine.