眼贴敷近距离放射治疗中的放射生物学以及利用目标函数评估植入物持续时间和放射性核素选择。
Radiobiology for eye plaque brachytherapy and evaluation of implant duration and radionuclide choice using an objective function.
机构信息
Department of Radiation Oncology, Tufts University School of Medicine, Boston, MA 02111, USA.
出版信息
Med Phys. 2012 Jun;39(6):3332-42. doi: 10.1118/1.4718683.
PURPOSE
Clinical optimization of Collaborative Ocular Melanoma Study (COMS) eye plaque brachytherapy is currently limited to tumor coverage, consensus prescription dosage, and dose calculations to ocular structures. The biologically effective dose (BED) of temporary brachytherapy treatments is a function of both chosen radionuclide R and implant duration T. This study endeavored to evaluate BED delivered to the tumor volume and surrounding ocular structures as a function of plaque position P, prescription dose, R, and T.
METHODS
Plaque-heterogeneity-corrected dose distributions were generated with MCNP5 for the range of currently available COMS plaques loaded with sources using three available low-energy radionuclides. These physical dose distributions were imported into the PINNACLE(3) treatment planning system using the TG-43 hybrid technique and used to generate dose volume histograms for a T = 7 day implant within a reference eye geometry including the ciliary body, cornea, eyelid, foveola, lacrimal gland, lens, optic disc, optic nerve, retina, and tumor at eight standard treatment positions. The equation of Dale and Jones was employed to create biologically effective dose volume histograms (BEDVHs), allowing for BED volumetric analysis of all ROIs. Isobiologically effective prescription doses were calculated for T = 5 days down to 0.01 days, with BEDVHs subsequently generated for all ROIs using correspondingly reduced prescription doses. Objective functions were created to evaluate the BEDVHs as a function of R and T. These objective functions are mathematically accessible and sufficiently general to be applied to temporary or permanent brachytherapy implants for a variety of disease sites.
RESULTS
Reducing T from 7 to 0.01 days for a 10 mm plaque produced an average BED benefit of 26%, 20%, and 17% for (103)Pd, (125)I, and (131)Cs, respectively, for all P; 16 and 22 mm plaque results were more position-dependent. (103)Pd produced a 16%-35% BED benefit over (125)I, whereas (131)Cs produced a 3%-7% BED detriment, independent of P, T, and plaque size. Additionally, corresponding organ at risk physical doses were lowest using (103)Pd in all circumstances.
CONCLUSIONS
The results suggest that shorter implant durations may correlate with more favorable outcomes compared to 7 day implants when treating small or medium intraocular lesions. The data also indicate that implant duration may be safely reduced if the prescription physical dose is likewise diminished and that (103)Pd offers a substantial radiobiological benefit over (125)I and (131)Cs irrespective of plaque position, implant duration, and tumor size.
目的
目前，对协作性眼黑色素瘤研究（COMS）眼贴剂近距离放射治疗的临床优化仅限于肿瘤覆盖范围、共识处方剂量和眼部结构的剂量计算。临时近距离放射治疗的生物有效剂量（BED）是所选放射性核素 R 和植入持续时间 T 的函数。本研究旨在评估肿瘤体积和周围眼部结构的 BED 作为斑块位置 P、处方剂量、R 和 T 的函数。
方法
使用 MCNP5 为目前可用于 COMS 斑块的各种源生成斑块不均匀性校正剂量分布。这些物理剂量分布使用 TG-43 混合技术导入 PINNACLE(3)治疗计划系统，并用于在参考眼几何形状内生成 T = 7 天植入物的剂量体积直方图，包括睫状体、角膜、眼睑、黄斑、泪腺、晶状体、视盘、视神经、视网膜和肿瘤在八个标准治疗位置。采用 Dale 和 Jones 方程生成生物有效剂量体积直方图（BEDVHs），允许对所有 ROI 进行 BED 体积分析。计算 T = 5 天至 0.01 天的等生物有效处方剂量，随后使用相应减少的处方剂量为所有 ROI 生成 BEDVHs。创建了目标函数来评估 R 和 T 作为 BEDVHs 的函数。这些目标函数在数学上是可访问的，并且足够通用，可以应用于各种疾病部位的临时或永久性近距离放射治疗植入物。
结果
对于 10mm 斑块，将 T 从 7 天减少到 0.01 天，对于所有 P；对于 16 和 22mm 斑块结果，对于（103）Pd、（125）I 和（131）Cs，分别产生了 26%、20%和 17%的平均 BED 益处，位置依赖性更强。（103）Pd 比（125）I 产生 16%-35%的 BED 益处，而（131）Cs 产生 3%-7%的 BED 危害，与 P、T 和斑块大小无关。此外，在所有情况下，使用（103）Pd 时对应的器官风险物理剂量最低。
结论
结果表明，与 7 天植入物相比，治疗小或中等眼内病变时，较短的植入持续时间可能与更有利的结果相关。数据还表明，如果处方物理剂量同样减少，并且（103）Pd 相对于（125）I 和（131）Cs 提供了显著的放射生物学益处，那么植入持续时间可以安全缩短，无论斑块位置、植入持续时间和肿瘤大小如何。
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