Hazuka M B, Ibbott G S, Kinzie J J
Division of Radiation Oncology, Presbyterian/Saint Luke's Medical Center, Denver, CO 80218.
Int J Radiat Oncol Biol Phys. 1988 Jun;14(6):1311-7. doi: 10.1016/0360-3016(88)90412-9.
Treatment of pelvic malignancies frequently includes the use of lateral, arc, or rotational fields. The presence of hip prostheses in these treatment fields will perturb the dose distribution. Correction factors for metal-based alloys used in artificial hips have not previously been reported. Prostheses constructed from frequently used alloys were obtained and measurements were made of the transmission of 4MV and 10MV photons. These measured data were compared with computed correction factors. The computer uses the "ratio of tissue-maximum ratios (TMR's)" method of heterogeneity correction. The computer was provided with both the physical density and the relative electron density of each prosthesis for comparison purposes, since electron densities for hip prostheses are not widely known. Correction factors determined from electron densities demonstrated better agreement with measured data. The "ratio of TMR's" correction algorithm does not consider the contribution of scattered radiation in the dose computations. Consequently, a small adjustment to the relative electron density of the prosthetic hip was required at lower X ray beam energies. Agreement was satisfactory for higher energy X rays, and thus no adjustment was necessary. Relative electron densities and adjusted electron densities for alloys used in artificial hips are provided for computer-aided treatment planning. Recommendations for incorporating the hip prosthesis into the treatment planning process are also provided.
盆腔恶性肿瘤的治疗通常包括使用侧野、弧形野或旋转野。这些治疗野中存在髋关节假体将会干扰剂量分布。此前尚未报道过用于人工髋关节的金属基合金的校正因子。获取了由常用合金制成的假体，并对4MV和10MV光子的透射率进行了测量。将这些测量数据与计算得到的校正因子进行了比较。计算机采用“组织最大剂量比（TMR）比值”方法进行不均匀性校正。为便于比较，向计算机提供了每个假体的物理密度和相对电子密度，因为髋关节假体的电子密度并不广为人知。由电子密度确定的校正因子与测量数据显示出更好的一致性。“TMR比值”校正算法在剂量计算中未考虑散射辐射的贡献。因此，在较低的X射线束能量下，需要对人工髋关节的相对电子密度进行小幅调整。对于较高能量的X射线，一致性令人满意，因此无需调整。提供了用于人工髋关节的合金的相对电子密度和调整后的电子密度，以用于计算机辅助治疗计划。还提供了将髋关节假体纳入治疗计划过程的建议。
