TY - JOUR
T1 - Simulation of pseudo-CT images based on deformable image registration of ultrasound images
T2 - A proof of concept for transabdominal ultrasound imaging of the prostate during radiotherapy
AU - Van Der Meer, Skadi
AU - Camps, Saskia M.
AU - Van Elmpt, Wouter J.C.
AU - Podesta, Mark
AU - Sanches, Pedro Gomes
AU - Vanneste, Ben G.L.
AU - Fontanarosa, Davide
AU - Verhaegen, Frank
N1 - Funding Information:
The authors would like to thank D. Bouvy, Professor Dr. J. P.W. Pluim, and in particular Dr. B. Reniers for their help and input on the DIR calculations. The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this paper: S.v.d.M. is partially funded by GROW (School for Oncology and Developmental Biology, Maastricht University ). The authors declared no potential conflict of interest with respect to the research, authorship, and/or publication of this paper.
Publisher Copyright:
© 2016 American Association of Physicists in Medicine.
PY - 2016/4
Y1 - 2016/4
N2 - Purpose: Imaging of patient anatomy during treatment is a necessity for position verification and for adaptive radiotherapy based on daily dose recalculation. Ultrasound (US) image guided radiotherapy systems are currently available to collect US images at the simulation stage (USsim), coregistered with the simulation computed tomography (CT), and during all treatment fractions. The authors hypothesize that a deformation field derived from US-based deformable image registration can be used to create a daily pseudo-CT (CTps) image that is more representative of the patients' geometry during treatment than the CT acquired at simulation stage (CTsim). Methods: The three prostate patients, considered to evaluate this hypothesis, had coregistered CT and US scans on various days. In particular, two patients had two US-CT datasets each and the third one had five US-CT datasets. Deformation fields were computed between pairs of US images of the same patient and then applied to the corresponding USsim scan to yield a new deformed CTps scan. The original treatment plans were used to recalculate dose distributions in the simulation, deformed and ground truth CT (CTgt) images to compare dice similarity coefficients, maximum absolute distance, and mean absolute distance on CT delineations and gamma index (γ) evaluations on both the Hounsfield units (HUs) and the dose. Results: In the majority, deformation did improve the results for all three evaluation methods. The change in gamma failure for dose (γDose, 3%, 3 mm) ranged from an improvement of 11.2% in the prostate volume to a deterioration of 1.3% in the prostate and bladder. The change in gamma failure for the CT images (γCT, 50 HU, 3 mm) ranged from an improvement of 20.5% in the anus and rectum to a deterioration of 3.2% in the prostate. Conclusions: This new technique may generate CTps images that are more representative of the actual patient anatomy than the CTsim scan.
AB - Purpose: Imaging of patient anatomy during treatment is a necessity for position verification and for adaptive radiotherapy based on daily dose recalculation. Ultrasound (US) image guided radiotherapy systems are currently available to collect US images at the simulation stage (USsim), coregistered with the simulation computed tomography (CT), and during all treatment fractions. The authors hypothesize that a deformation field derived from US-based deformable image registration can be used to create a daily pseudo-CT (CTps) image that is more representative of the patients' geometry during treatment than the CT acquired at simulation stage (CTsim). Methods: The three prostate patients, considered to evaluate this hypothesis, had coregistered CT and US scans on various days. In particular, two patients had two US-CT datasets each and the third one had five US-CT datasets. Deformation fields were computed between pairs of US images of the same patient and then applied to the corresponding USsim scan to yield a new deformed CTps scan. The original treatment plans were used to recalculate dose distributions in the simulation, deformed and ground truth CT (CTgt) images to compare dice similarity coefficients, maximum absolute distance, and mean absolute distance on CT delineations and gamma index (γ) evaluations on both the Hounsfield units (HUs) and the dose. Results: In the majority, deformation did improve the results for all three evaluation methods. The change in gamma failure for dose (γDose, 3%, 3 mm) ranged from an improvement of 11.2% in the prostate volume to a deterioration of 1.3% in the prostate and bladder. The change in gamma failure for the CT images (γCT, 50 HU, 3 mm) ranged from an improvement of 20.5% in the anus and rectum to a deterioration of 3.2% in the prostate. Conclusions: This new technique may generate CTps images that are more representative of the actual patient anatomy than the CTsim scan.
KW - adaptive radiotherapy
KW - deformable image registration
KW - image guided radiotherapy
KW - prostate cancer
KW - ultrasound imaging
UR - http://www.scopus.com/inward/record.url?scp=84962145303&partnerID=8YFLogxK
U2 - 10.1118/1.4944064
DO - 10.1118/1.4944064
M3 - Review article
C2 - 27036587
AN - SCOPUS:84962145303
SN - 0094-2405
VL - 43
SP - 1913
EP - 1920
JO - Medical Physics
JF - Medical Physics
IS - 4
ER -
