Medical Physics Unit, European Institute of Oncology, Milan, Italy.
Eur J Nucl Med Mol Imaging. 2013 Jul;40(7):1047-56. doi: 10.1007/s00259-013-2383-1. Epub 2013 May 3.
A novel method for prostate irradiation is investigated. Similarly to (125)I or (103)Pd seed brachytherapy, (90)Y-avidin could be injected via the perineum under ultrasound image guidance. This study inspects the theoretical feasibility with a dosimetric model based on Monte Carlo simulation.
A geometrical model of the prostate, urethra and rectum was designed. The linear-quadratic model was applied to convert (125)I absorbed dose prescription/constraints into (90)Y dose through biological effective dose (BED) calculation. The optimal (90)Y-avidin injection strategy for the present model was obtained. Dose distribution was calculated by Monte Carlo simulation (PENELOPE,GEANT4). Dose volume histograms (DVH) for the prostate, urethra and rectum were compared to typical DVHs of (125)I seed brachytherapy, used routinely in our institute.
With (90)Y-avidin, at least 95% of the prostate must receive more than 70 Gy. The absorbed dose to 10% of the urethra (D(10%_urethra)) and the maximum absorbed dose to the rectum (D(max_rectum)) must be lower than 122 Gy. For the present model, the optimum strategy consists in multiple injections of (90)Y-avidin 50 μl drops, for a total volume of 3.1 ml. The minimum activity to deliver the prescribed absorbed dose is 0.7 GBq, which also fully respects urethral and rectal constraints. The resulting dose map has a maximum in the central region with a sharp decrease towards the urethra and the prostate edge. Notably, D(10%_urethra) is 95 Gy and D(max_rectum) is below 2 Gy. Prostate absorbed dose is higher with (90)Y-avidin than (125)I seeds, although the total volume receiving the prescribed absorbed dose is 1-2% lower. Urethral DVH strictly depends on the (90)Y distribution, to be optimized according to prostate shape; in our model, BED(30%_urethra) is 90 Gy with (90)Y-avidin, whereas for patients receiving (125)I seeds it ranges between 150 and 230 Gy. The rectal DVH is always more favourable with (90)Y.
The methodology is theoretically feasible and can deliver an effective treatment in T1-T2 prostate cancer. Pharmacokinetic and biodistribution studies in prostate cancer patients are needed for validation.
研究一种新的前列腺放射治疗方法。类似于（125）I 或（103）Pd 种子近距离放射治疗，（90）Y-亲和素可以通过经会阴超声引导下注入。本研究通过基于蒙特卡罗模拟的剂量学模型来检查理论可行性。
设计了前列腺、尿道和直肠的几何模型。应用线性二次模型通过生物有效剂量（BED）计算将（125）I 吸收剂量处方/约束转换为（90）Y 剂量。获得了当前模型的最佳（90）Y-亲和素注射策略。通过蒙特卡罗模拟（PENELOPE、GEANT4）计算剂量分布。将前列腺、尿道和直肠的剂量体积直方图（DVH）与我们研究所常规使用的典型（125）I 种子近距离放射治疗的 DVH 进行比较。
用（90）Y-亲和素，至少 95%的前列腺必须接受超过 70 Gy 的剂量。尿道的 10%吸收剂量（D（10%_urethra））和直肠的最大吸收剂量（D（max_rectum））必须低于 122 Gy。对于当前的模型，最佳策略是多次注射（90）Y-亲和素 50 μl 液滴，总量为 3.1 ml。输送规定吸收剂量所需的最小活度为 0.7 GBq，同时也完全符合尿道和直肠的约束条件。所得剂量图在中央区域有一个最大值，然后向尿道和前列腺边缘急剧下降。值得注意的是，D（10%_urethra）为 95 Gy，D（max_rectum）低于 2 Gy。与（125）I 种子相比，（90）Y-亲和素的前列腺吸收剂量更高，尽管接受规定吸收剂量的总体积低 1-2%。尿道的 DVH 严格取决于（90）Y 的分布，需要根据前列腺的形状进行优化；在我们的模型中，（90）Y-亲和素的 BED（30%_urethra）为 90 Gy，而接受（125）I 种子的患者则在 150 至 230 Gy 之间。直肠的 DVH 总是更有利于（90）Y。
该方法在理论上是可行的，可以为 T1-T2 期前列腺癌提供有效的治疗。需要在前列腺癌患者中进行药代动力学和生物分布研究以进行验证。
