Li X Allen, Wang Jian Z, Stewart Robert D, DiBiase Steven J
Department of Radiation Oncology, University of Maryland, School of Medicine, 22 South Greene Street, Baltimore, MD 21201-1595, USA.
Phys Med Biol. 2003 Sep 7;48(17):2753-65. doi: 10.1088/0031-9155/48/17/302.
No prospective dose escalation study for prostate brachytherapy (PB) with permanent implants has been reported. In this work, we have performed a dosimetric and biological analysis to explore the implications of dose escalation in PB using 125I and 103Pd implants. The concept of equivalent uniform dose (EUD), proposed originally for external-beam radiotherapy (EBRT), is applied to low dose rate brachytherapy. For a given 125I or 103Pd PB, the EUD for tumour that corresponds to a dose distribution delivered by EBRT is calculated based on the linear quadratic model. The EUD calculation is based on the dose volume histogram (DVH) obtained retrospectively from representative actual patient data. Tumour control probabilities (TCPs) are also determined in order to compare the relative effectiveness of different dose levels. The EUD for normal tissue is computed using the Lyman model. A commercial inverse treatment planning algorithm is used to investigate the feasibility of escalating the dose to prostate with acceptable dose increases in the rectum and urethra. The dosimetric calculation is performed for five representative patients with different prostate sizes. A series of PB dose levels are considered for each patient using 125I and 103Pd seeds. It is found that the PB prescribed doses (minimum peripheral dose) that give an equivalent EBRT dose of 64.8, 70.2, 75.6 and 81 Gy with a fraction size of 1.8 Gy are 129, 139, 150 and 161 Gy for 125I and 103, 112, 122 and 132 Gy for 103Pd implants, respectively. Estimates of the EUD and TCP for a series of possible prescribed dose levels (e.g., 145, 160, 170 and 180 Gy for 125I and 125, 135, 145 and 155 for 103Pd implants) are tabulated. The EUD calculation was found to depend strongly on DVHs and radiobiological parameters. The dosimetric calculations suggest that the dose to prostate can be escalated without a substantial increase in both rectal and urethral dose. For example, increasing the PB prescribed dose from 145 to 180 Gy increases EUD for the rectum by only 3%. Our studies indicate that the dose to urethra can be kept within 100-120% of the prescription dose for all the dose levels studied. In conclusion, dose escalation in permanent implant for localized prostate cancer may be advantageous. It is dosimetrically possible to increase dose to prostate without a substantial increase in the dose to the rectum and urethra. Based on the results of our studies, a prospective dose escalation trial for prostate permanent implants has been initiated at our institution.
尚无关于永久性植入物前列腺近距离放射治疗（PB）的前瞻性剂量递增研究报告。在本研究中，我们进行了剂量学和生物学分析，以探讨使用¹²⁵I和¹⁰³Pd植入物进行PB剂量递增的影响。最初为外照射放疗（EBRT）提出的等效均匀剂量（EUD）概念被应用于低剂量率近距离放射治疗。对于给定的¹²⁵I或¹⁰³Pd PB，基于线性二次模型计算与EBRT所给予剂量分布相对应的肿瘤EUD。EUD计算基于从代表性实际患者数据中回顾性获得的剂量体积直方图（DVH）。还确定了肿瘤控制概率（TCP），以比较不同剂量水平的相对有效性。使用莱曼模型计算正常组织的EUD。使用商业逆向治疗计划算法研究在直肠和尿道剂量可接受增加的情况下增加前列腺剂量的可行性。对五名具有不同前列腺大小的代表性患者进行剂量学计算。对于每位患者，使用¹²⁵I和¹⁰³Pd种子考虑一系列PB剂量水平。结果发现，对于¹²⁵I植入物，当分割剂量为1.8 Gy时，给予等效EBRT剂量64.8、70.2、75.6和81 Gy的PB处方剂量（最小周边剂量）分别为129、139、150和161 Gy，对于¹⁰³Pd植入物分别为103、112、122和132 Gy。列出了一系列可能的处方剂量水平（例如，¹²⁵I植入物为145、160、170和180 Gy，¹⁰³Pd植入物为125、135、145和155）的EUD和TCP估计值。发现EUD计算强烈依赖于DVH和放射生物学参数。剂量学计算表明，可以在不显著增加直肠和尿道剂量的情况下增加前列腺剂量。例如，将PB处方剂量从145 Gy增加到180 Gy时，直肠的EUD仅增加3%。我们的研究表明，在所研究的所有剂量水平下，尿道剂量可保持在处方剂量的100 - 120%以内。总之，局部前列腺癌永久性植入物的剂量递增可能是有利的。在剂量学上有可能增加前列腺剂量而不显著增加直肠和尿道剂量。基于我们的研究结果，我们机构已启动一项关于前列腺永久性植入物的前瞻性剂量递增试验。
