Kato Takahiro, Kato Masato, Takemasa Kimihiro, Murakami Masao
Department of Radiation Physics and Technology, Southern Tohoku Proton Therapy Center, Fukushima, Japan.
Department of Radiological Sciences, School of Health Sciences, Fukushima Medical University, Fukushima, Japan.
J Med Phys. 2022 Oct-Dec;47(4):331-335. doi: 10.4103/jmp.jmp_85_22. Epub 2023 Jan 10.
To quantitatively evaluate how much the doses to organs at risk are affected in the prone position compared to the supine position in the proton therapy (PT) for prostate cancer.
Fifteen consecutive patients with clinically localized prostate cancer underwent treatment planning computed tomography scans in both the supine and prone positions. The clinical target volume (CTV) consisted of the prostate gland plus the seminal vesicles. The PT plans were designed using the standard lateral opposed fields with passively scattered proton beams for both treatment positions. The prescribed dose for each plan was set to 78 Gy (Relative biological effectiveness)/39 fractions to 50% of the planning target volume. Dose-volume metrics of the rectum and bladder in the two treatment positions were analyzed.
It was confirmed that all the parameters of D, D, D, D, D, and V examined in the rectum were significantly reduced in the prone position. There was no significant difference between the two positions in the bladder dose except for D. The distance between the CTV and the rectum tended to increase with the patient in the prone position; at the prostate level, however, the maximum change was approximately 5 mm, and there was significant variation between cases.
We confirmed that the rectal doses were significantly lower in the prone compared with the supine position in PT. Although uncertain, the prone position could be an effective method to reduce the rectal dose in PT.
定量评估在前列腺癌质子治疗（PT）中，与仰卧位相比，俯卧位时危及器官所受剂量受到的影响程度。
15例临床局限性前列腺癌患者连续接受了仰卧位和俯卧位的治疗计划计算机断层扫描。临床靶区（CTV）包括前列腺和精囊。两种治疗体位的PT计划均采用标准的侧野对穿照射，使用被动散射质子束。每个计划的处方剂量设定为78 Gy（相对生物效应）/39次分割照射至计划靶区体积的50%。分析了两种治疗体位下直肠和膀胱的剂量体积指标。
证实直肠中所检测的D、D、D、D、D和V的所有参数在俯卧位时均显著降低。除D外，两种体位的膀胱剂量无显著差异。CTV与直肠之间的距离在患者俯卧位时趋于增加；然而，在前列腺水平，最大变化约为5 mm，且病例之间存在显著差异。
我们证实，在PT中，俯卧位时直肠剂量明显低于仰卧位。尽管存在不确定性，但俯卧位可能是降低PT中直肠剂量的有效方法。
