第五讲-tps system.pptVIP

Life cycle of Linac TPS 新买的Linac Acceptance test – 其目的是确认厂家安装的Linac满足我们预购的指标 (beam energy, beam flatness symmetry, etc) 测很少一组数据 (PDD, profiles)，验证其参数 TPS commissioning – 其目的是通过大量的测量数据，优化TPS的beam model参数，目标是TPS计算的剂量(PDD, profiles)与测量值匹配 一旦确定，基本上不会改变 Routine Linac 质量保证 (Daily, Monthly, Annual) 其目的是检测Linac的输出稳定性；以commissioning data作为参照-这样TPS 计算和Linac输出总能匹配 * Data measurement AAPM TG 106 as guideline PDD and beam profiles (两个方向） Field sizes- 2x2, 3x3, 5x5, 10x10, 20x20, 30x30,40x40 cm2 Depth- Dmax, 5, 10, 20, 30 cm Additional PDD 4x4, 6x6, 8x8, 12x12, 15x15, 18x18, 25x25 cm2 Asymmetric MLC beam profile Open Jaw wide to 20 cm Move MLC bank to 0, ±5 cm, ±10 cm, ±15 cm Output factors/TG-51… * 问题? * * * * * * * * * * * * * * * * * * 基于模型的剂量计算 Convolution/Superposition methods （卷积/叠加算法） * 几个重要的物理概念 几个重要的与剂量计算相关的物理概念 KERMA TERMA Absorbed Dose Photon energy fluence Ψ Coefficients Mass energy transfer coefficient utr/ρ Mass energy absorption coefficient uab/ρ Mass attenuation coefficient u/ρ Khan, The Physics of Radiation Therapy * TERMA TERMA: Total energy released in the medium, defined as total radiant energy released per unit mass by primary photons in a medium total energy (Energy of electron + energy of scatter photon) 只考虑primary photons,不考虑从介质中其它地方scatter过来的photons * Absorbed dose Absorbed dose, or simply dose, is the quotient dE/dm, where dE is the mean energy imparted by ionizing radiation to material of mass dm. 简而言之，dose = 单位质量吸收的能量 TERMA和Dose的单位-MeV/g * Energy fluence Courtesy - EB Podgorsak, Radiation oncology phyiscs: a handbook 假想有个很小的小球，其截面积是dA，energy fluence刻画有多少能量穿过这个截面; 单位 – MeV/cm2 * Coefficients 系数 不是很严格的理解，系数就是比例,单位 cm2/g Attenuation coefficients - u/ρ 衰减系数-多少比例的粒子会产生反应 Energy transfer coefficients - utr/ρ 能量传递-多少比例的能量会传递给介质 Energy absorption coefficients - uen/ρ 能量吸收-多少比例的能量会被介质吸收 * TERMA计算 TERMA: Total energy released, by primary photons where Ψp is energy fluence of primary photons at a point, and ??/?? is mean mass attenuation coeff