Department of Radiation Oncology, Tufts University School of Medicine, Boston, MA 02111, USA.
Med Phys. 2012 Feb;39(2):976-83. doi: 10.1118/1.3679010.
A method is introduced to examine the influence of implant duration T, radionuclide, and radiobiological parameters on the biologically effective dose (BED) throughout the entire volume of regions of interest for episcleral brachytherapy using available radionuclides. This method is employed to evaluate a particular eye plaque brachytherapy implant in a radiobiological context.
A reference eye geometry and 16 mm COMS eye plaque loaded with (103)Pd, (125)I, or (131)Cs sources were examined with dose distributions accounting for plaque heterogeneities. For a standardized 7 day implant, doses to 90% of the tumor volume ( (TUMOR)D(90)) and 10% of the organ at risk volumes ( (OAR)D(10)) were calculated. The BED equation from Dale and Jones and published α/β and μ parameters were incorporated with dose volume histograms (DVHs) for various T values such as T = 7 days (i.e., (TUMOR) (7)BED(10) and (OAR) (7)BED(10)). By calculating BED throughout the volumes, biologically effective dose volume histograms (BEDVHs) were developed for tumor and OARs. Influence of T, radionuclide choice, and radiobiological parameters on (TUMOR)BEDVH and (OAR)BEDVH were examined. The nominal dose was scaled for shorter implants to achieve biological equivalence.
(TUMOR)D(90) values were 102, 112, and 110 Gy for (103)Pd, (125)I, and (131)Cs, respectively. Corresponding (TUMOR) (7)BED(10) values were 124, 140, and 138 Gy, respectively. As T decreased from 7 to 0.01 days, the isobiologically effective prescription dose decreased by a factor of three. As expected, (TUMOR) (7)BEDVH did not significantly change as a function of radionuclide half-life but varied by 10% due to radionuclide dose distribution. Variations in reported radiobiological parameters caused (TUMOR) (7)BED(10) to deviate by up to 46%. Over the range of (OAR)α/β values, (OAR) (7)BED(10) varied by up to 41%, 3.1%, and 1.4% for the lens, optic nerve, and lacrimal gland, respectively.
BEDVH permits evaluation of the relative biological effectiveness for brachytherapy implants. For eye plaques, (TUMOR)BEDVH and (OAR)BEDVH were sensitive to implant duration, which may be manipulated to affect outcomes.
介绍一种方法，以检查植入物持续时间 T、放射性核素和放射生物学参数对眼外膜近距离放射治疗中感兴趣区域整个体积的生物有效剂量（BED）的影响，使用现有的放射性核素。该方法用于在放射生物学背景下评估特定的眼斑近距离放射治疗植入物。
使用考虑到斑块不均匀性的剂量分布，检查了参考眼几何形状和装有 (103)Pd、(125)I 或 (131)Cs 源的 16 毫米 COMS 眼斑。对于标准化的 7 天植入物，计算了肿瘤体积 90%（TUMOR）D(90)和 10%的风险器官体积（OAR）D(10)的剂量。Dale 和 Jones 的 BED 方程和已发表的 α/β 和 μ 参数与各种 T 值的剂量体积直方图（DVH）结合使用，例如 T=7 天（即 TUMOR(7)BED(10)和 OAR(7)BED(10)）。通过计算整个体积的 BED，为肿瘤和 OAR 开发了生物有效剂量体积直方图（BEDVH）。研究了 T、放射性核素选择和放射生物学参数对 TUMORBEDVH 和 OARBEDVH 的影响。为了实现生物学等效，将名义剂量缩小到较短的植入物。
（103）Pd、（125）I 和（131）Cs 的 TUMOR）D(90)值分别为 102、112 和 110 Gy。相应的 TUMOR(7)BED(10)值分别为 124、140 和 138 Gy。当 T 从 7 天降至 0.01 天时，等生物有效处方剂量降低了三倍。正如预期的那样，TUMOR(7)BEDVH 不会因放射性核素半衰期而显著变化，但由于放射性核素剂量分布而变化 10%。报告的放射生物学参数的变化导致 TUMOR(7)BED(10)偏差高达 46%。在 OARα/β 值的范围内，晶状体、视神经和泪腺的 OAR(7)BED(10)分别变化高达 41%、3.1%和 1.4%。
BEDVH 允许评估近距离放射治疗植入物的相对生物效应。对于眼斑，TUMORBEDVH 和 OARBEDVH 对植入物持续时间敏感，可进行操作以影响结果。
