Dosimetry of 125I and 103Pd COMS eye plaques for intraocular tumors: Report of Task Group 129 by the AAPM and ABS
Dosimetry of 125I and 103Pd COMS eye plaques for intraocular tumors: Report of Task Group 129 by the AAPM and ABS
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DOI：
10.1118/1.4749933
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发表时间：
2012-10-01
期刊：
影响因子：
3.8
通讯作者：
Thomson, Rowan M.
中科院分区：
文献类型：
--
作者：
Chiu-Tsao, Sou-Tung;Astrahan, Melvin A.;Thomson, Rowan M.
眼肿瘤斑块的剂量测定在近距离治疗中提出了独特的挑战。精确剂量测定的挑战部分与肿瘤和距离放射源不到毫米的关键结构中的陡峭剂量梯度有关。在大多数临床应用中，眼斑周围剂量分布的计算都假定为均匀的水介质和完全散射条件。最近基于蒙特卡罗（MC）的眼斑剂量模拟表明，包括金合金衬底和硅橡胶衬垫在内的异质材料在眼斑中的扰动效应可以以合理的精度计算出来。甚至通过使用金箔“种子指南”和定制设计的牌匾引入的额外复杂程度也可以使用现代MC技术精确计算。考虑到上述复杂性的模拟表明，与常规剂量计算相比，对选定的关键结构的剂量差异超过十倍。成立了129任务小组来审查文献；重新审视目前的剂量学计算形式；并提出眼斑剂量学的建议，包括近距离治疗源剂量学参数的评价和异质性校正因子。文献综述确定了协作性眼黑色素瘤研究（COMS）设计斑块剂量计算的现代评估，包括MC分析和治疗计划系统（TPS）的相互比较，详细说明了使用美国医学物理学家协会（AAPM） TG-43U1近距离治疗剂量计量形式和MC技术的均匀和非均匀斑块计算之间的差异。本综述发现，考虑到COMS斑块的异质性，在均匀介质中，通常使用的处方剂量为85 Gy，深度为5mm，对于特定的I-125和Pd-103源，剂量分别为75 Gy和69 Gy，深度为相同的5mm。因此，在临床实践中采用异质剂量计算方法会导致剂量差异达10%，需要仔细评估处方剂量的相应变化。正常眼结构的剂量随放射性核素、斑块位置和处方深度的选择而变化，因此需要对采用基于mc的剂量学方法进行进一步的剂量学评估。AAPM和美国近距离放射治疗学会（ABS）建议临床医学物理学家使用本报告表格中的信息同时估计异质性校正的放射剂量，为近距离放射治疗TPS做准备，该TPS可以解释材料的异质性，并过渡到异质性校正的规定目标。建议近距离TPS供应商在其系统中包括材料异质性校正，并采取措施整合计划的斑块定位和图像引导。在商用mc为基础的近距离放射治疗TPS可用之前，建议临床医学物理学家使用均匀水介质中的线源近似和2D AAPM TG-43U1剂量学形式和近距离放射治疗源剂量学参数数据集进行治疗计划计算。此外，本报告还包括眼斑近距离治疗的质量管理方案建议。(C) 2012年美国医学物理学家协会。[http://dx.doi.org/10.1118/1.4749933]
Dosimetry of eye plaques for ocular tumors presents unique challenges in brachytherapy. The challenges in accurate dosimetry are in part related to the steep dose gradient in the tumor and critical structures that are within millimeters of radioactive sources. In most clinical applications, calculations of dose distributions around eye plaques assume a homogenous water medium and full scatter conditions. Recent Monte Carlo (MC)-based eye-plaque dosimetry simulations have demonstrated that the perturbation effects of heterogeneous materials in eye plaques, including the gold-alloy backing and Silastic insert, can be calculated with reasonable accuracy. Even additional levels of complexity introduced through the use of gold foil "seed-guides" and custom-designed plaques can be calculated accurately using modern MC techniques. Simulations accounting for the aforementioned complexities indicate dose discrepancies exceeding a factor of ten to selected critical Structures compared to conventional dose calculations. Task Group 129 was formed to review the literature; re-examine the current dosimetry calculation formalism; and make recommendations for eye-plaque dosimetry, including evaluation of brachytherapy source dosimetry parameters and heterogeneity correction factors. A literature review identified modern assessments of dose calculations for Collaborative Ocular Melanoma Study (COMS) design plaques, including MC analyses and an intercomparison of treatment planning systems (TPS) detailing differences between homogeneous and heterogeneous plaque calculations using the American Association of Physicists in Medicine (AAPM) TG-43U1 brachytherapy dosimetry formalism and MC techniques. This review identified that a commonly used prescription dose of 85 Gy at 5 mm depth in homogeneous medium delivers about 75 Gy and 69 Gy at the same 5 mm depth for specific I-125 and Pd-103 sources, respectively, when accounting for COMS plaque heterogeneities. Thus, the adoption of heterogeneous dose calculation methods in clinical practice would result in dose differences >10% and warrant a careful evaluation of the corresponding changes in prescription doses. Doses to normal ocular structures vary with choice of radionuclide, plaque location, and prescription depth, such that further dosimetric evaluations of the adoption of MC-based dosimetry methods are needed. The AAPM and American Brachytherapy Society (ABS) recommend that clinical medical physicists should make concurrent estimates of heterogeneity-corrected delivered dose using the information in this report's tables to prepare for brachytherapy TPS that can account for material heterogeneities and for a transition to heterogeneity-corrected prescriptive goals. It is recommended that brachytherapy TPS vendors include material heterogeneity corrections in their systems and take steps to integrate planned plaque localization and image guidance. In the interim, before the availability of commercial MC-based brachytherapy TPS, it is recommended that clinical medical physicists use the line-source approximation in homogeneous water medium and the 2D AAPM TG-43U1 dosimetry formalism and brachytherapy source dosimetry parameter datasets for treatment planning calculations. Furthermore, this report includes quality management program recommendations for eye-plaque brachytherapy. (C) 2012 American Association of Physicists in Medicine. [http://dx.doi.org/10.1118/1.4749933]