Department of Radiotherapy, Mohamed V Military Hospital, Rabat, Morocco.
Cancer Radiother. 2021 Apr;25(2):161-168. doi: 10.1016/j.canrad.2020.06.033. Epub 2021 Jan 14.
The aims of this study were: determination of the CTV to PTV margins for prostate and pelvic lymph nodes. Investigation of the impact of registration modality (pelvic bones or prostate) on the CTV to PTV margins of pelvic lymph nodes. Investigation of the variations of bladder and rectum over the treatment course. Investigation of the impact of bladder and rectum variations on prostate position.
This study included 15 patients treated for prostate adenocarcinoma. Daily kilo voltage images and weekly CBCT scans were performed to assess prostate displacements and common and external iliac vessels motion. These data was used to calculate the CTV to PTV margins using Van Herk equation in the setting of a daily bone registration. We also compared the CTV to PTV margins of pelvic lymph nodes according to registration method; based on pelvic bone or prostate. We delineated bladder and rectum on all CBCT scans to assess their variations over treatment course at 4 anatomic levels [1.5cm above pubic bone (PB), superior edge, mid- and inferior edge of PB].
Using Van Herk equation, the prostate CTV to PTV margins (bone registration) were 8.03mm, 5.42mm and 8.73mm in AP, ML and SI direction with more than 97% of prostate displacements were less than 5mm. The CTV to PTV margins ranged from 3.12mm to 3.25mm for external iliac vessels and from 3.12mm to 4.18mm for common iliac vessels. Compared to registration based on prostate alignment, bone registration resulted in an important reduction of the CTV to PTV margins up to 54.3% for external iliac vessels and up to 39.6% for common iliac vessels. There was no significant variation of the mean bladder volume over the treatment course. There was a significant variation of the mean rectal volume before and after the third week of treatment. After the third week, the mean rectal volume seemed to be stable. The uni- and multivariate analysis identified the anterior wall of rectum as independent factor acting on prostate motion in AP direction at 2 levels (superior edge of, mid PB). The right rectal wall influenced the prostate motion in ML direction at inferior edge of PB. The bladder volume tends toward significance as factor acting on prostate motion in AP direction.
We recommend CTV to PTV margins of 8mm, 6mm and 9mm in AP, ML and SI directions for prostate. And, we suggest 4mm and 5mm for external and common iliac vessels respectively. We also prefer registration based on bony landmarks to minimize bowel irradiation. More CBCT scans should be performed during the first 3weeks and especially the first week to check rectum volume.
本研究旨在确定前列腺和盆腔淋巴结CTV 到 PTV 的边缘。研究注册方式（骨盆或前列腺）对盆腔淋巴结CTV 到 PTV 边缘的影响。研究膀胱和直肠在治疗过程中的变化。研究膀胱和直肠变化对前列腺位置的影响。
本研究纳入了 15 名接受前列腺腺癌治疗的患者。每天进行千伏图像和每周锥形束 CT 扫描，以评估前列腺的位移以及髂内血管的运动。这些数据用于根据每日骨注册计算 Van Herk 方程中的 CTV 到 PTV 边缘。我们还根据注册方法（骨盆或前列腺）比较了盆腔淋巴结的 CTV 到 PTV 边缘。我们在所有 CBCT 扫描上勾画了膀胱和直肠，以评估在 4 个解剖水平[耻骨上方 1.5cm（PB）、上边缘、PB 中部和下部]上治疗过程中的变化。
使用 Van Herk 方程，前列腺 CTV 到 PTV 边缘（骨注册）在 AP、ML 和 SI 方向上分别为 8.03mm、5.42mm 和 8.73mm，超过 97%的前列腺位移小于 5mm。髂外血管CTV 到 PTV 边缘范围为 3.12mm 至 3.25mm，髂内血管CTV 到 PTV 边缘范围为 3.12mm 至 4.18mm。与基于前列腺对准的注册相比，骨注册导致 CTV 到 PTV 边缘的重要减少，髂外血管减少高达 54.3%，髂内血管减少高达 39.6%。在治疗过程中，膀胱平均体积没有明显变化。治疗第 3 周前后直肠平均体积有显著变化。第 3 周后，直肠平均体积似乎稳定。单变量和多变量分析确定直肠前壁是在 AP 方向上影响前列腺运动的独立因素，在 2 个水平（PB 上缘、PB 中部）上。右直肠壁影响 PB 下缘 ML 方向上的前列腺运动。膀胱体积在 AP 方向上影响前列腺运动，这一因素有显著意义。
我们建议前列腺 CTV 到 PTV 边缘分别为 8mm、6mm 和 9mm，在 AP、ML 和 SI 方向上。我们还建议髂外和髂内血管分别为 4mm 和 5mm。我们还建议基于骨性标志进行注册，以尽量减少肠道照射。在前 3 周，特别是第 1 周，应进行更多的 CBCT 扫描，以检查直肠体积。
