Newhauser Wayne D, Koch Nicholas C, Fontenot Jonas D, Rosenthal Stanley J, S Gombos Dan, Fitzek Markus M, Mohan Radhe
The University of Texas M D Anderson Cancer Center, 1515 Holcombe Boulevard, Unit 94, Houston, TX 77030, USA.
Phys Med Biol. 2007 Jul 7;52(13):3979-90. doi: 10.1088/0031-9155/52/13/021. Epub 2007 Jun 6.
Metallic fiducial markers are frequently implanted in patients prior to external-beam radiation therapy to facilitate tumor localization. There is little information in the literature, however, about the perturbations in proton absorbed-dose distribution these objects cause. The aim of this study was to assess the dosimetric impact of perturbations caused by 2.5 mm diameter by 0.2 mm thick tantalum fiducial markers when used in proton therapy for treating uveal melanoma. Absorbed dose perturbations were measured using radiochromic film and confirmed by Monte Carlo simulations of the experiment. Additional Monte Carlo simulations were performed to study the effects of range modulation and fiducial placement location on the magnitude of the dose shadow for a representative uveal melanoma treatment. The simulations revealed that the fiducials caused perturbations in the absorbed-dose distribution, including absorbed-dose shadows of 22% to 82% in a typical proton beam for treating uveal melanoma, depending on the marker depth and orientation. The clinical implication of this study is that implanted fiducials may, in certain circumstances, cause dose shadows that could lower the tumor dose and theoretically compromise local tumor control. To avoid this situation, fiducials should be positioned laterally or distally with respect to the target volume.
在进行外照射放疗之前，常常会在患者体内植入金属基准标记物，以方便肿瘤定位。然而，文献中关于这些物体对质子吸收剂量分布的扰动的信息却很少。本研究的目的是评估直径2.5毫米、厚度0.2毫米的钽基准标记物在用于质子治疗葡萄膜黑色素瘤时所引起的扰动对剂量测定的影响。使用放射变色胶片测量吸收剂量扰动，并通过对实验的蒙特卡罗模拟进行验证。还进行了额外的蒙特卡罗模拟，以研究范围调制和基准放置位置对典型葡萄膜黑色素瘤治疗中剂量阴影大小的影响。模拟结果显示，基准标记物会引起吸收剂量分布的扰动，在治疗葡萄膜黑色素瘤的典型质子束中，根据标记物的深度和方向，吸收剂量阴影在22%至82%之间。本研究的临床意义在于，在某些情况下，植入的基准标记物可能会导致剂量阴影，从而降低肿瘤剂量，并在理论上影响局部肿瘤控制。为避免这种情况，基准标记物应相对于靶体积横向或向远端放置。
