Division of Medical Physics and Department of Radiation Oncology, Rajiv Gandhi Cancer Institute and Research Centre, New Delhi (India)-110085, India.
Amity School of Applied Sciences, Amity University (AUUP), NOIDA, India.
Asian Pac J Cancer Prev. 2020 Jun 1;21(6):1731-1738. doi: 10.31557/APJCP.2020.21.6.1731.
Aim of study is to investigate the effect of hip prosthesis on 6 and 15 MV photon beam energies.
Prosthesis was kept at the level of tray position. The measurements were done on Varian Clinac-iX linac. Customized prosthesis, termed as Prosthetic Metal Implant (PMI) was made up of wrought austenitic stainless steel rod and covered with paraffin-wax. 'Standard prosthesis' was made up of wrought titanium alloy. The dose profiles were measured for three field sizes i.e. 5, 10 and 20 cm at 100 cm SSD for 6 and 15 MV energies. The perturbation index (PI) was also calculated.
Perturbation caused by standard prosthesis was approximately 50% higher than that of PMI. This result may be due to difference in dimension and not because of material composition. Variation of central axis dose might be due to the dimensions of PMI used for experiment which gave intermediate response (e.g. 102.1%, 141.0% and 117.7% for Open, Standard and PMI respectively for 10x10 cm2 field size, 10 cm depth and 15MV photon beam setup )as compared to the 'open' and 'standard' prosthesis. Percentage dose at 10 cm for 6MV photon increased rapidly with field-size for PMI. But, for 15MV photon, difference was not significant. Surface dose (Ds) for PMI remains significantly higher for smaller field.
The perturbation index varied from 0.05 to 0.22 for the measured energies and gave an idea to the planner to assess the behavior of the prosthesis. This range is applicable for both type of implants and for all clinical field-sizes. The attenuation caused by the prosthesis was significant and this effect should be considered in the treatment planning calculations.
本研究旨在探讨髋关节假体对 6 兆伏和 15 兆伏光子束能的影响。
将假体保持在托盘位置。测量在瓦里安 Clinac-iX 直线加速器上进行。定制的假体称为假体金属植入物（PMI），由锻造奥氏体不锈钢棒制成，并覆盖石蜡。“标准假体”由锻造钛合金制成。在 SSD 为 100cm 时，测量了三个射野尺寸（5、10 和 20cm）的剂量分布，用于 6 和 15MV 能量。还计算了扰动量（PI）。
标准假体引起的扰动量比 PMI 高约 50%。这一结果可能是由于尺寸的差异，而不是由于材料成分的差异。中心轴剂量的变化可能是由于用于实验的 PMI 尺寸所致，其给出了中间响应（例如，对于 10x10cm2 射野尺寸、10cm 深度和 15MV 光子束设置，Open、Standard 和 PMI 的中心轴剂量分别为 102.1%、141.0%和 117.7%）与“Open”和“Standard”假体相比。6MV 光子的 10cm 处的百分剂量随 PMI 的射野尺寸迅速增加。然而，对于 15MV 光子，差异不显著。对于较小的射野，PMI 的表面剂量（Ds）仍然显著较高。
测量能量的扰动量指数在 0.05 到 0.22 之间变化，为规划师提供了评估假体行为的想法。该范围适用于两种类型的植入物和所有临床射野尺寸。假体引起的衰减是显著的，在治疗计划计算中应考虑这一影响。
