TY - JOUR
T1 - Using daily diagnostic quality images to validate planning margins for prostate interfractional variations
AU - Li, Wen
AU - Vassil, Andrew
AU - Godley, Andrew
AU - Mossolly, Lama Muhieddine
AU - Shang, Qingyang
AU - Xia, Ping
N1 - Publisher Copyright:
© 2016 Creative Commons Attribution 4.0 International License.
PY - 2016
Y1 - 2016
N2 - The purpose of this study is to use the same diagnostic-quality verification and planning CTs to validate planning margin account for residual interfractional variations with image-guided soft tissue alignment of the prostate. For nine prostate cancer patients treated with IMRT to 78 Gy in 39 fractions, daily verification CT-on-rails images of the first seven and last seven fractions (n = 126) were retrospectively selected for this study. On these images, prostate, bladder, and rectum were delineated by the same attending physician. Clinical plans were created with a margin of 8 mm except for 5 mm posteriorly, referred to as 8/5mm. Three additional plans were created for each patient with the margins of 6/4 mm, 4/2mm, and 2 mm uniform. These plans were subsequently applied to daily images and radiation doses were recalculated. The isocenters of these plans were placed according to clinical online shifts, which were based on soft tissue alignment to the prostate. Retrospective offline shifts by aligning prostate contours were compared to online shifts. The resultant daily target dose was analyzed using D99, the percentage of the prescription dose received by 99% of CTV. The percent of bladder volume receiving 65 Gy (V65Gy) and rectum V70Gy were also analyzed. After interfractional correction, using CTV D99 > 97% criteria, 8/5 mm, 6/4 mm, 4/2 mm, and 2 mm planning margins met the CTV dose coverage in 95%, 91%, 65%, and 53% of the 126 fractions with online shifts, and 99%, 98%, 85%, and 68% with offline shifts. The rectum V70Gy and bladder V65Gy were significantly decreased at each level of margin reduction (p < 0.05). With daily diagnostic quality imaging-guidance, the interfractional planning margin may be reduced from 8/5mm to 6/4 mm. The residual interfractional uncertainties most likely stem from prostate rotation anddeformation.
AB - The purpose of this study is to use the same diagnostic-quality verification and planning CTs to validate planning margin account for residual interfractional variations with image-guided soft tissue alignment of the prostate. For nine prostate cancer patients treated with IMRT to 78 Gy in 39 fractions, daily verification CT-on-rails images of the first seven and last seven fractions (n = 126) were retrospectively selected for this study. On these images, prostate, bladder, and rectum were delineated by the same attending physician. Clinical plans were created with a margin of 8 mm except for 5 mm posteriorly, referred to as 8/5mm. Three additional plans were created for each patient with the margins of 6/4 mm, 4/2mm, and 2 mm uniform. These plans were subsequently applied to daily images and radiation doses were recalculated. The isocenters of these plans were placed according to clinical online shifts, which were based on soft tissue alignment to the prostate. Retrospective offline shifts by aligning prostate contours were compared to online shifts. The resultant daily target dose was analyzed using D99, the percentage of the prescription dose received by 99% of CTV. The percent of bladder volume receiving 65 Gy (V65Gy) and rectum V70Gy were also analyzed. After interfractional correction, using CTV D99 > 97% criteria, 8/5 mm, 6/4 mm, 4/2 mm, and 2 mm planning margins met the CTV dose coverage in 95%, 91%, 65%, and 53% of the 126 fractions with online shifts, and 99%, 98%, 85%, and 68% with offline shifts. The rectum V70Gy and bladder V65Gy were significantly decreased at each level of margin reduction (p < 0.05). With daily diagnostic quality imaging-guidance, the interfractional planning margin may be reduced from 8/5mm to 6/4 mm. The residual interfractional uncertainties most likely stem from prostate rotation anddeformation.
KW - Diagnostic image
KW - Interfraction
KW - Planning margins
KW - Prostate cancer
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U2 - 10.1120/jacmp.v17i3.5923
DO - 10.1120/jacmp.v17i3.5923
M3 - Article
C2 - 27167262
AN - SCOPUS:84968833680
SN - 1526-9914
VL - 17
SP - 61
EP - 74
JO - Journal of applied clinical medical physics
JF - Journal of applied clinical medical physics
IS - 3
ER -