Automated weekly replanning for intensity-modulated radiotherapy of cervix cancer.
OBJECTIVE
The adoption of intensity-modulated radiotherapy (IMRT) to treat cervical malignancies has been limited in part by complex organ and tumor motion during treatment. This study explores the limits of a highly adaptive, small-margin treatment scenario to accommodate this motion. In addition, the dosimetric consequences of organ and tumor motion are modeled using a combination of deformable registration and fractional dose accumulation techniques.


METHODS
Thirty-three cervix cancer patients had target volumes and organs-at-risk contoured on fused, pretreatment magnetic resonance-computed tomography images and weekly magnetic resonance scans taken during treatment. The dosimetric impact of interfraction organ and target motion was compared for two hypothetical treatment scenarios: a 3-mm margin plan with no replanning, and a 3-mm margin plan with an automated replan performed on the updated weekly patient geometry.


RESULTS
Of the 33 patients, 24 (73%) met clinically acceptable target coverage (98% of the clinical target volume receiving at least 95% of the prescription dose) using the 3-mm margin plan without replanning. The range in dose to 98% of the clinical target volume across all patients was 7.9% of the prescription dose if no replanning was performed. After weekly replanning, this range was tightened to 2.6% of the prescription dose and all patients met clinically acceptable target coverage while maintaining organ-at-risk dose sparing.


CONCLUSIONS
The dosimetric impact of anatomical motion underscores the challenges of applying IMRT to treat cervix cancer. An appropriate adaptive strategy can ensure target coverage for small-margin IMRT treatments and maintain favorable organ-at-risk dose sparing.
Stewart
James
J
Princess Margaret Hospital/Ontario Cancer Institute, University Health Network, Toronto, Canada.
Lim
Karen
K
Kelly
Valerie
V
Xie
Jason
J
Brock
Kristy K
KK
Moseley
Joanne
J
Cho
Young-Bin
YB
Fyles
Anthony
A
Lundin
Anna
A
Rehbinder
Henrik
H
Löf
Johan
J
Jaffray
David
D
Milosevic
Michael
M
D000328:Adult; D000368:Aged; D019583:Dose Fractionation, Radiation; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods; D008875:Middle Aged; D009068:Movement; D011446:Prospective Studies; D011832:Radiation Injuries / Q000517:prevention & control; D011880:Radiotherapy Planning, Computer-Assisted; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D013997:Time Factors; D014057:Tomography, X-Ray Computed; D047368:Tumor Burden; D002583:Uterine Cervical Neoplasms / Q000473:pathology / Q000532:radiotherapy*