Impact of daily soft-tissue image guidance to prostate on pelvic lymph node (PLN) irradiation for prostate patients receiving SBRT Journal Article


Authors: Tyagi, N.; Hipp, E.; Cloutier, M.; Charas, T.; Fontenla, S.; Mechalakos, J.; Hunt, M.; Zelefsky, M.
Article Title: Impact of daily soft-tissue image guidance to prostate on pelvic lymph node (PLN) irradiation for prostate patients receiving SBRT
Abstract: Purpose: To determine the impact of using fiducial match for daily image-guidance on pelvic lymph node (PLN) coverage for prostate cancer patients receiving stereotactic body radiation therapy (SBRT). Methods: Thirty patients underwent SBRT treatment to the prostate and PLN from 2014 to 2016. Each patient received either 800cGy × 5 or 500cGy × 5 to the prostate and 500cGy × 5 to the PLN. A 5 mm clinical target volume (CTV)-to-planning target volume (PTV) margin around the PLN was used for planning. Two registrations with planning computed tomography (PCT) for each of the daily cone beam CTs (CBCTs) were performed: a rigid registration to fiducials and to the bony anatomy. The average translational difference between fiducial and bony match as well as percentage of fractions with differences > 5mm were calculated. Changes in bladder and rectal volume as well as center-of-mass (COM) position from simulation parameters, and their correlation with translational difference were also evaluated. The dosimetric impact of the translational differences was calculated by shifting the plan isocenter. Results: The average translational difference between fiducial and bony match was 0.06 ± 0.82, 2.1 ± 4.1, −2.8 ± 4.3, and 5.5 ± 4.2 mm for lateral, vertical, longitudinal, and vector directions. The average change in bladder and rectal volume from simulation was −67.2 ± 163.04 cc (−12 ± 52%) and −1.6 ± 18.75 (−2 ± 30%) cc. The average change in COM of bladder from the simulation position was 0.34 ± 2.49, 4.4 ± 8.1, and −3.9 ± 7.5 mm along the LR, AP, and SI directions. The corresponding COM change for the rectum was 0.17 ± 1.9, 1.34 ± 3.5, and −0.6 ± 5.2 mm. Conclusions: The 5 mm margin covered ~75% of fractions receiving PLN irradiation with SBRT, daily CBCT and fiducial-guided setup. The dosimetric impact on PLN coverage was significant in 19% of fractions or 25% of patients. A larger translational shift was due to variation in rectal volume and changes in COM position of the bladder and rectum. A consistent bladder positioning and/or rectum filling compared with presimulation volume were essential for adequate coverage of PLN in a hypofractionated treatment regime. © 2019 The Authors. Journal of Applied Clinical Medical Physics published by Wiley Periodicals, Inc. on behalf of American Association of Physicists in Medicine.
Keywords: prostate cancer; image guidance; stereotactic body radiation therapy; pelvic lymph node
Journal Title: Journal of Applied Clinical Medical Physics
Volume: 20
Issue: 7
ISSN: 1526-9914
Publisher: American College of Medical Physics  
Date Published: 2019-07-01
Start Page: 121
End Page: 127
Language: English
DOI: 10.1002/acm2.12665
PUBMED: 31206236
PROVIDER: scopus
PMCID: PMC6612686
DOI/URL:
Notes: Article -- Export Date: 2 August 2019 -- Source: Scopus
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MSK Authors
  1. Michael J Zelefsky
    655 Zelefsky
  2. Margie A Hunt
    251 Hunt
  3. Neelam Tyagi
    65 Tyagi
  4. Tomer Menahem Charas
    7 Charas
  5. Elizabeth Hipp
    4 Hipp