An analysis of interfractional and intrafractional prostate motion in hypofractionated precise radiotherapy for prostate cancer / 中华放射肿瘤学杂志

ABSTRACT

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.