Analysis of Motion-dependent Clinical Outcome of Tumor Tracking Stereotactic Body Radiotherapy for Prostate Cancer

BACKGROUND: To analyze clinical outcome of CyberKnife (CK) tumor-tracking stereotactic body radiotherapy (SBRT) for prostate cancer (Pca) according to the magnitude of intra-fractional prostate motion. METHODS: Medical records and daily treatment logs for 71 patients who received CK tumor-tracking SBRT were retrospectively analyzed. Statistical relationships between prostate motion and various outcome results, including local recurrence (LR), biochemical failure (BF), and treatment-related toxicity, were investigated in order to evaluate motion-dependent efficacy of tumor-tracking SBRT for Pca. RESULTS: In a total 71 patients, 3 (4.2%) patients with LR, 12 (16.9%) patients with BF, and 22 (31%) patients with grade-II or worse toxicities to rectal or bladder (22 to rectal, 22 to bladder and 8 patients to both) were observed in a median follow-up of 47 months. Magnitudes of intra-fractional tumor motion along superior-inferior, right-left, and anterior-posterior (AP) axes were 0.15 ± 0.31, 0.12 ± 0.19, and 0.73 ± 0.32 mm, respectively. Radial magnitude was estimated to be 1.0 ± 0.35 mm. Intra-fractional movement was not significantly correlated with tumor control. However, it was significant correlated with the incidence of grade-II or worse toxicity to rectum or bladder particularly when tumor motion was in the AP axis. CONCLUSION: Our quantitative results revealed that toxicity related to SBRT treatment was highly sensitive to intra-fractional prostate movements, although local-tumor control was not affected by such movements. Our results demonstrate that precise motion correction is essential in prostate SBRT, even if it seems to be small.

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

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.