Dosimetric impact of intra-fraction prostate motion under a tumour-tracking system in hypofractionated robotic radiosurgery.

Yuhei Koike,Hirokazu Mizuno,Keita Kurosu,Osamu Suzuki,Kazuhiko Ogawa,Hiroya Shiomi,Keisuke Tamari,Iori Sumida,Yasuo Yoshioka,Seiichi Ota,Qinghui Zhang

doi:10.1371/journal.pone.0195296

Yuhei Koike, Hirokazu Mizuno + Show 9 more

Open Access

https://doi.org/10.1371/journal.pone.0195296

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Journal: PloS one	Publication Date: Apr 5, 2018
Citations: 12	License type: CC BY 4.0

Affiliation: Osaka University, Osaka University Hospital

Abstract

For CyberKnife-mediated prostate cancer treatment, a tumour-tracking approach is applied to correct the target location by acquiring X-ray images of implanted fiducial markers intermittently. This study investigated the dosimetric impact of intra-fraction prostate motion during CyberKnife treatment. We retrospectively analyzed 16 patients treated using the CyberKnife (35 Gy delivered in five fractions). Using log files of recorded prostate motion, the intra-fraction prostate motion was simulated. We defined the worst-case intra-fraction prostate motion as the difference between pre- and post-deviation on log files and shifted structure sets according to the corresponding offsets for each beam. The dose–volume indices were calculated and compared with the original plan in terms of clinical target volume (CTV), planning target volume (CTV plus a 2-mm margin), rectum, bladder, and urethra. Prostate motions of >3, >5, and >10 mm were observed for 31.3, 9.1, and 0.5% of the 1929 timestamps, respectively. Relative differences between the simulated and original plans were mostly less than 1%. Although significant decreases were observed in D50% and D98% of the target, absolute dose differences were <0.1 Gy compared with the planned dose. The dosimetric impact of intra-fraction prostate motion may be small even with longer treatment durations, indicating that the tumour tracking using the CyberKnife could be a robust system for examining prostate motion.

Highlights

Hypofractionated stereotactic body radiation therapy (SBRT) is an attractive strategy for prostate cancer in terms of radiobiology in that the alpha-beta ratio for prostate cancer is small (1.5 Gy) [1,2]
To minimize the uncertainty of prostate motion, various image-guided techniques have been developed and introduced for hypofractionated SBRT, such as cone-beam computed tomography (CT), electronic portal imaging device, ultrasound, and electromagnetic transponders, which are classified as realtime or nearly real-time monitoring systems [5,6,7,8,9]
The findings from this study suggest that the dosimetric impact of intra-fraction prostate motion may be small with the mean timestamp interval about 70 s

Summary

Introduction

Hypofractionated stereotactic body radiation therapy (SBRT) is an attractive strategy for prostate cancer in terms of radiobiology in that the alpha-beta ratio for prostate cancer is small (1.5 Gy) [1,2]. Dosimetric impact of intra-fraction prostate motion in hypofractionated radiosurgery conventional fractionated dose (2 Gy per fraction), a slight positional error may result in urinary and rectal side effects as well as insufficient dose coverage [3]. To minimize the uncertainty of prostate motion, various image-guided techniques have been developed and introduced for hypofractionated SBRT, such as cone-beam computed tomography (CT), electronic portal imaging device, ultrasound, and electromagnetic transponders, which are classified as realtime or nearly real-time monitoring systems [5,6,7,8,9]

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