前列腺癌大分割精确放疗分次治疗间和分次治疗内位置变动分析

An analysis of interfractional and intrafractional prostate motion in hypofractionated precise radiotherapy for prostate cancer

目的：了解前列腺癌精确大分割放疗时分次间和分次内前列腺靶区位移情况。方法对2013—2016年间28例接受5 Gy9次放疗的前列腺癌患者，定位前2周B超引导下经直肠穿刺前列腺内植入纯金标记3颗，仰卧位体膜固定充盈膀胱并直肠内插置直肠扩张球囊充气60 ml后CT定位，Pinnacle系统制定放疗计划。23例患者Synergy加速器治疗，每次疗前CBCT校位，扫描图像与计划图像行骨配准记录摆位误差，然后通过前列腺内金标位置配准记录前列腺位移误差，两次之差为分次间位移。5例患者Novalis加速器治疗，通过前列腺内金标配准，疗中ExacTrac系统实时跟踪金标位置变化，观察前列腺分次内位移。结果23例患者每次疗前均测量位移共计207次，左右、上下、前后位移平均值分别为（0．05±0.10）、（0．20±0.22）、（0．19±0.18） cm；3个方向＞0.3 cm位移分别为1、52、49次，＞0.5 cm位移分别为1、29、16次。5例患者每次放疗时监测测量金标位置移动5次共计225次，左右、上下、前后位移平均值分别为（0．61±0.50）、（0．68±0.69）、（0．70±0.67） mm，各方向＞3 mm移动分别为0、1、1次。结论前列腺癌精确大分割放疗时分次间位移远远大于分次内位移，分次间位移必须校正后才能放疗。分次内靶区位移尽管变化较小，但仍有必要监测分次内靶区位移，以防患者体位变动造成靶区脱靶照射。直肠内球囊插入对前列腺位置具有固定作用。

Objective To investigate the interfractional and intrafractional prostate motion during hypofractionated precise radiotherapy for prostate cancer. Methods From 2013 to 2016, twenty.eight patients who received 5 Gy radiotherapy in 9 fractions for prostate cancer were enrolled as subjects. Every patient had three gold fiducials implanted into the prostate by transrectal ultrasound guidance two weeks before computed tomography （ CT） simulation. All patients underwent CT scans in the supine position with full bladders and rectal balloons filled with 60 ml air. The Pinnacle planning system was used to design the treatment plans. Twenty.three patients were treated with a Synergy accelerator. Those patients underwent cone.beam CT （ CBCT） scans prior to treatment. The set.up error was recorded by bone alignment between CBCT images and planning CT images. The prostate displacement was then recorded by gold fiducial alignment. The interfraction prostate displacement was defined by the difference between the above two parameters. The other 5 patients were treated with a Novalis accelerator. Based on gold fiducial alignment,the real.time tracking of gold fiducials was carried out by the ExacTrac system to evaluate the intrafractional prostate displacement. Results A total of 207 measurements of interfractional prostate displacement were made in the 23 patients before treatment. The mean interfractional prostate displacements in the left.right （LR）,superior.inferior （SI）,and anterior.posterior （AP） directions were （0.05±0.10）,（0.20±0.22）,and（0.19±0.18） cm,respectively. The displacements larger than 0.3 cm in the above three directions were observed in 1,52,and 49 measurements,respectively,while the displacements larger than 0.5 cm in the three directions were observed in 1,29,and 16 measurements,respectively. A total of 225 measurements of gold fiducial displacement were made in the 5 patients during treatment. The mean intrafractional prostate displacements in LR,SI,and AP directions were （0.61±0.50）,（0.68±0.69）,and （0.70±0.67） mm, respectively. The displacements larger than 3 mm in the three directions were observed in 0, 1, and 1 measurement, respectively. Conclusions In hypofractionated precise radiotherapy for prostate cancer, the interfractional prostate displacement is significantly larger than the intrafractional prostate displacement. The interfractional prostate displacement must be corrected before radiotherapy. In order to avoid off.target irradiation due to postural changes in patients,the tracking of the intrafractional prostate displacement is still necessary although the displacement is relatively small. The rectal balloon can help immobilize the prostate.