Merrick G S, Butler W M, Dorsey A T, Lief J H, Donzella J G
Schiffler Cancer Center, Wheeling Hospital, Wheeling, WV 26003-6300, USA.
Int J Radiat Oncol Biol Phys. 2000 Nov 1;48(4):1069-74. doi: 10.1016/s0360-3016(00)00746-x.
The etiology of erectile dysfunction after definitive local therapy for carcinoma of the prostate gland represents a multifactorial phenomenon including neurogenic compromise, venous insufficiency, local trauma, and psychogenic causes. It has been suggested that impotence after prostate brachytherapy is a consequence of excessive radiation dose to the neurovascular bundles (NVB). Herein we evaluate the potential relationship between radiation dose to the NVB and the development of erectile dysfunction following prostate brachytherapy.
The radiation dose to the NVB was evaluated for 33 patients who developed erectile dysfunction (ED) following brachytherapy plus 21 additional patients who were potent before and subsequent to brachytherapy. Of the 54 patient study group, the median follow up was 37 months, and 25 patients were managed with (125)I as a monotherapeutic approach and 29 received (103)Pd as a boost following 45 Gy of external beam radiation therapy. Radiographic localization of the NVB was performed via a two-dimensional geometric model that placed 3-NVB calculation points on the left and right posterolateral side of each 5-mm CT slice. Parameters evaluated included dose-surface histograms, dose parameters via point doses on each slice, the magnitude of the dose in relationship to the distance from the base, and the relationship between NVB radiation dose in patients with and without ED, patient response to sildenafil and case sequence number.
In terms of percent prescribed minimum peripheral dose (% mPD), there was no significant difference in mean neurovascular bundle dose between potent and impotent patients, between the isotopes ((125)I or (103)Pd), mono- or boost therapy, or side of the prostate for which the overall average was 217% +/- 55% of mPD. There was also no significant dosimetric difference in terms of response to sildenafil based on a multivariate analysis which included % mPD and various dose thresholds and side of the gland. The dose distribution over the length of the prostate rose smoothly from the base and apex to peak at midgland in (125)I implants while (103)Pd implants had a relatively constant dose over the length of the prostate. Considering the calculation grid as forming a 6-mm wide ribbon along each side of the prostate, the average patient had 70 mm(2) area receiving at least 300% of mPD.
In this study, no relationship between radiation dose to the NVB and the development of post brachytherapy erectile dysfunction was discernible. Such a difference may become evident with additional follow-up. If long-term brachytherapy-induced erectile dysfunction is related to the radiation dose to the NVB, the ultimate preservation of potency following prostate brachytherapy may be markedly inferior to what has been reported. Nevertheless, the majority of this patient population responded favorably to sildenafil.
前列腺癌确定性局部治疗后勃起功能障碍的病因是一种多因素现象，包括神经源性损害、静脉功能不全、局部创伤和心理因素。有人提出，前列腺近距离放射治疗后阳痿是神经血管束（NVB）接受过量辐射剂量的结果。在此，我们评估NVB辐射剂量与前列腺近距离放射治疗后勃起功能障碍发生之间的潜在关系。
对33例近距离放射治疗后出现勃起功能障碍（ED）的患者以及另外21例在近距离放射治疗前后均有勃起功能的患者的NVB辐射剂量进行评估。在54例患者的研究组中，中位随访时间为37个月，25例患者采用（125）I作为单一治疗方法，29例患者在接受45 Gy外照射放疗后接受（103）Pd作为增强治疗。通过二维几何模型对NVB进行影像学定位，该模型在每个5 mm CT切片的左右后外侧放置3个NVB计算点。评估的参数包括剂量-表面直方图、通过每个切片上的点剂量得出的剂量参数、剂量大小与距基部距离的关系，以及有和没有ED的患者的NVB辐射剂量之间的关系、患者对西地那非的反应和病例序号。
就规定的最小周边剂量百分比（% mPD）而言，有勃起功能和无勃起功能的患者之间、同位素（（125）I或（103）Pd）之间、单一治疗或增强治疗之间，或前列腺两侧之间的平均神经血管束剂量没有显著差异，总体平均值为mPD的217%±55%。基于多变量分析，在对西地那非的反应方面也没有显著的剂量学差异，该分析包括% mPD和各种剂量阈值以及腺体侧别。在（125）I植入物中，前列腺长度上的剂量分布从基部和尖部平稳上升至腺体中部达到峰值，而（103）Pd植入物在前列腺长度上的剂量相对恒定。将计算网格视为沿前列腺每侧形成一条6 mm宽的带，平均每位患者有70 mm²的区域接受至少300%的mPD。
在本研究中，未发现NVB辐射剂量与近距离放射治疗后勃起功能障碍的发生之间存在关联。随着进一步随访，这种差异可能会变得明显。如果长期近距离放射治疗引起的勃起功能障碍与NVB辐射剂量有关，那么前列腺近距离放射治疗后勃起功能的最终保留情况可能明显低于已报道的情况。然而，该患者群体中的大多数对西地那非反应良好。
