国家ＩＥＣ标准规定，关于医用高能电子直线加速器治疗对称性指标应控制在电子线≤＋５％，光子线≤＋３％。超过该标准的治疗机，应严格调整合格后方能用于临床治疗。最近，我们遇到一例有关电路而非参数调整引起的对称性故障。故障现象：各能量档治疗显示窗口都出现ＥＸＱ１ National IEC standards stipulate that the symmetry indicators for medical high-energy electron linear accelerators should be controlled at the electronic line ≤ +5% and the photonic lines ≤ +3%. Therapeutic machines that exceed this standard should be strictly adjusted for clinical use. Recently, we encountered an example of a symmetry failure caused by a circuit rather than a parameter adjustment. Symptoms: EXQ1 appears in the energy display window