Optimizing fiducial visibility on periodically acquired megavoltage and kilovoltage image pairs during prostate volumetric modulated arc therapy Journal Article


Authors: Zhang, P.; Happersett, L.; Ravindranath, B.; Zelefsky, M.; Mageras, G.; Hunt, M.
Article Title: Optimizing fiducial visibility on periodically acquired megavoltage and kilovoltage image pairs during prostate volumetric modulated arc therapy
Abstract: Purpose: Robust detection of implanted fiducials is essential for monitoring intrafractional motion during hypofractionated treatment. The authors developed a plan optimization strategy to ensure clear visibility of implanted fiducials and facilitate 3D localization during volumetric modulated arc therapy (VMAT). Methods: Periodic kilovoltage (kV) images were acquired at 20° gantry intervals and paired with simultaneously acquired 4.4° short arc megavoltage digital tomosynthesis (MV-DTS) to localize three fiducials during VMAT delivery for hypofractionated prostate cancer treatment. Beginning with the original optimized plan, control point segments where fiducials were consistently blocked by multileaf collimator (MLC) within each 4.4° MV-DTS interval were first identified. For each segment, MLC apertures were edited to expose the fiducial that led to the least increase in the cost function. Subsequently, MLC apertures of all control points not involved with fiducial visualization were reoptimized to compensate for plan quality losses and match the original dose-volume histogram. MV dose for each MV-DTS was also kept above 0.4 MU to ensure acceptable image quality. Different imaging (gantry) intervals and visibility margins around fiducials were also evaluated. Results: Fiducials were consistently blocked by the MLC for, on average, 36% of the imaging control points for five hypofractionated prostate VMAT plans but properly exposed after reoptimization. Reoptimization resulted in negligible dosimetric differences compared with original plans and outperformed simple aperture editing: on average, PTV D98 recovered from 87% to 94% of prescription, and PTV dose homogeneity improved from 9% to 7%. Without violating plan objectives and compromising delivery efficiency, the highest imaging frequency and largest margin that can be achieved are a 10° gantry interval, and 15 mm, respectively. Conclusions: VMAT plans can be made to accommodate MV-kV imaging of fiducials. Fiducial visualization rate and workflow efficiency are significantly improved with an automatic modification and reoptimization approach. © 2016 American Association of Physicists in Medicine.
Keywords: vmat; intrafraction motion management; mv/kv tracking
Journal Title: Medical Physics
Volume: 43
Issue: 5
ISSN: 0094-2405
Publisher: American Association of Physicists in Medicine  
Date Published: 2016-05-01
Start Page: 2024
End Page: 2029
Language: English
DOI: 10.1118/1.4944737
PROVIDER: scopus
PMCID: PMC4826385
PUBMED: 27147314
DOI/URL:
Notes: Article -- Export Date: 2 June 2016 -- Source: Scopus
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MSK Authors
  1. Michael J Zelefsky
    755 Zelefsky
  2. Pengpeng Zhang
    180 Zhang
  3. Gikas S Mageras
    277 Mageras
  4. Margie A Hunt
    287 Hunt