Impact of hydrogel peri-rectal spacer insertion on prostate gland intra-fraction motion during 1.5 T MR-guided stereotactic body radiotherapy

Abstract

Background: The assessment of organ motion is a crucial feature for prostate stereotactic body radiotherapy (SBRT). Rectal spacer may represent a helpful device in order to outdistance rectal wall from clinical target, but its impact on organ motion is still a matter of debate. MRI-Linac is a new frontier in radiation oncology as it allows a superior visualization of the real-time anatomy of the patient and the current highest level of adaptive radiotherapy. Methods: We present data regarding a total of 100 fractions in 20 patients who underwent MRI-guided prostate SBRT for low-to-intermediate risk prostate cancer with or without spacer. Translational and rotational shifts were computed on the pre-and post-treatment MRI acquisitions referring to the delivery position for antero-posterior, latero-lateral and cranio-caudal direction, and assessed using the Mann-Whitney U-Test. Results: All patients were treated with a five sessions schedule (35 Gy/5fx) using MRI-Linac for a median fraction treatment time of 50 min (range, 46-65). In the entire study sample, median rotational displacement was 0.1°in cranio-caudal, − 0.002°in latero-lateral and 0.01°in antero-posterior direction; median translational shift was 0.11 mm in cranio-caudal, − 0.24 mm in latero-lateral and − 0.22 mm in antero-posterior. A significant difference between spacer and no-spacer patients in terms of rotational shifts in the antero-posterior direction (p = 0.033) was observed; also for translational shifts a positive trend was detected in antero-posterior direction (p = 0.07), although with no statistical significance. We observed statistically significant differences in the pre-treatment planning phase in favor of the spacer cohort for several rectum dose constraints: rectum V32Gy < 5% (p = 0.001), V28 Gy < 10% (p = 0.001) and V18Gy < 35% (p = 0.039). Also for bladder V35 Gy < 1 cc, the use of spacer provided a dosimetric advantage compared to the no-spacer subpopulation (p = 0.04). Furthermore, PTV V33.2Gy > 95% was higher in the spacer cohort compared to the no-spacer one (p = 0.036).

Intra-fraction displacement of the prostate bed during post-prostatectomy radiotherapy

“…This variation might occur because real-time monitoring detects transient excursion which cannot be detected with pre and post-treatment imaging. When comparing to the definitive prostate setting Cuccia et al found that the intra-fraction median translational displacement was 0.11 mm in SI, − 0.24 mm in LR, and − 0.22 mm in AP which is smaller than what was detected in our prostate bed cohort [13].…”

Reply to Ghaffari et al. “In regard to Cuccia et al.: impact of hydrogel peri-rectal spacer insertion on prostate gland intra-fraction motion during 1.5 T MR-guided stereotactic body radiotherapy.”

“…Reply to Ghaffari et al "In regard to Cuccia et al: impact of hydrogel peri-rectal spacer insertion on prostate gland intra-fraction motion during 1.5 T MR-guided stereotactic body radiotherapy." Francesco Cuccia 1* and Filippo Alongi 1,2 We kindly thank the letter by Ghaffari et al [1] for their interesting observations concerning our recent study about the potential impact of hydrogel spacer on prostate intrafraction motion during 1.5 T MR-guided stereotactic body radiotherapy [2].…”

Injection of hydrogel spacer increased intrafractional prostate motion during volumetric modulated arc therapy-stereotactic body radiation therapy for prostate cancer

“…Picardi et al (19) showed that hydrogel spacer injection into the recto-prostatic space did not signi cantly in uence the interfraction prostate motion based on the analysis using implanted ducial markers and CBCT. It was reported that hydrogel spacer insertion signi cantly reduced the intrafraction rotational shift in the AP direction on cine-MRI by Cuccia et al (20) and they concluded that hydrogel spacer contributed to limiting prostate intrafractional motion. On the other hand, Juneja et al (18) showed that the average of the mean intrafractional vector displacement of prostate was signi cantly larger in patients with hydrogel spacer than those without spacer by analyzing the implanted electromagnetic markers position on kV uoroscopy.…”

“…The injection of hydrogel spacer between the prostate and the rectum has been introduced for RT for PCa to separate the prostate from the anterior wall of the rectum, which contributes to reducing the RT dose of the rectum. It was shown that the insertion of hydrogel spacer did not greatly limit interfractional and intrafractional prostate displacements (18)(19)(20). We hypothesized that the hydrogel spacer potentially implicates the prostate variability during RT.…”