Nakamura Ryuji, Ishiyama Hiromichi, Tanji Susumu, Satoh Takefumi, Oikawa Hirobumi, Inatsu Wakako, Ehara Shigeru, Hayakawa Kazushige
Department of Radiology, Iwate Medical University School of Medicine, Morioka, Iwate, Japan.
Brachytherapy. 2011 May-Jun;10(3):208-13. doi: 10.1016/j.brachy.2010.01.002. Epub 2010 Aug 4.
To elucidate the potential effects of prostate deformation on dose distribution during Iodine-125 ((125)I) seed implantation brachytherapy for prostate cancer.
A retrospective analysis of 245 patients who underwent only transperineal brachytherapy for low-risk prostate adenocarcinoma was performed. The maximum diameters of the prostate were measured before treatment by transrectal ultrasound volumetry along right to left (RL), anterior to posterior (AP), and apex to base (Length) directions. The seeds were inserted by the modified peripheral loading method using real-time ultrasound-guided seed placement. The ellipsoid deformation rates in the axial plane (E(ax)) and in the sagittal plane (E(sag)) were defined as [RL-AP]/RL and [Length-AP]/Length, respectively. The correlation between them and the dose-volume histogram parameters at 30 days after the operation was evaluated. A simulation test was additionally performed to ascertain the change in dose distribution among virtual volumes built in a radiotherapy planning device that corresponds to prostates with increased Eax or Esag.
The mean Esag and Eax of patients were 0.313 (range, -0.28 to 0.844) and 0.261 (range, -0.02 to 0.54), respectively. Esag showed a positive correlation with dose (Gy) covering 90% of the prostate volume (pD(90)), prostate volume (%) covered by 100% of the prescribed dose (pV(100)), the rectal volume (cc) irradiated by 100% of the prescribed dose (rV(100)), and the rectal volume (cc) irradiated by 150% of the prescribed dose (rV(150)), whereas Eax showed a positive correlation with prostate volume (%) covered by 150% of the prescribed dose (pV(150)) and the urethral dose (Gy) delivered to 5% of its volume (uD(5)). The simulation test suggested that the prescribed dose resulted in the best coverage in patients with increased E(sag), and that patients with increased E(ax) exhibited poor urethral sparing from overdosage.
In the seed implantation method, ellipsoid deformation of the prostate causes higher rectal dose exposure or dose delivery to the urethra.
阐明前列腺变形对碘-125（¹²⁵I）粒子植入近距离放射治疗前列腺癌过程中剂量分布的潜在影响。
对245例仅接受经会阴近距离放射治疗的低危前列腺腺癌患者进行回顾性分析。治疗前通过经直肠超声容积测量法沿左右（RL）、前后（AP）和尖部至底部（长度）方向测量前列腺的最大直径。采用改良的周边加载法并利用实时超声引导粒子植入。轴向平面（E(ax)）和矢状平面（E(sag)）的椭球体变形率分别定义为[RL - AP]/RL和[长度 - AP]/长度。评估它们与术后30天剂量体积直方图参数之间的相关性。另外进行模拟测试，以确定在放射治疗计划设备中构建的对应于Eax或Esag增加的前列腺的虚拟体积之间剂量分布的变化。
患者的平均Esag和Eax分别为0.313（范围，-0.28至0.844）和0.261（范围，-0.02至0.54）。Esag与覆盖90%前列腺体积的剂量（Gy）（pD(90)）、被100%处方剂量覆盖的前列腺体积（%）（pV(100)）、被100%处方剂量照射的直肠体积（cc）（rV(100)）以及被150%处方剂量照射的直肠体积（cc）（rV(150)）呈正相关，而Eax与被150%处方剂量覆盖的前列腺体积（%）（pV(150)）以及输送至尿道5%体积的尿道剂量（Gy）（uD(5)）呈正相关。模拟测试表明，对于E(sag)增加的患者，处方剂量能实现最佳覆盖，而E(ax)增加的患者尿道免受过量照射的情况较差。
在粒子植入方法中，前列腺的椭球体变形会导致更高的直肠剂量暴露或向尿道的剂量输送。
