Pelvic radiotherapy for cancer of the cervix: is what you plan actually what you deliver?
OBJECTIVE
Whole pelvic intensity-modulated radiotherapy (IMRT) is increasingly being used to treat cervix cancer and other gynecologic tumors. However, tumor and normal organ movement during treatment can substantially detract from the benefits of this approach. This study explored the effect of internal anatomic changes on the dose delivered to the tumor and organs at risk using a strategy integrating deformable soft-tissue modeling with simulated dose accumulation.


METHODS
Twenty patients with cervix cancer underwent baseline and weekly pelvic magnetic resonance imaging during treatment. Interfraction organ motion and delivered (accumulated) dose was modeled for three treatment scenarios: four-field box, large-margin whole pelvic IMRT (20-mm planning target volume, but 10 mm inferiorly) and small-margin IMRT (5-mm planning target volume).


RESULTS
Individually, the planned dose was not the same as the simulated delivered dose; however, when taken as a group, this was not statistically significant for the four-field box and large-margin IMRT plans. The small-margin IMRT plans yielded adequate target coverage in most patients; however, significant target underdosing occurred in 1 patient who displayed excessive, unpredictable internal target movement. The delivered doses to the organs at risk were significantly reduced with the small-margin plan, although substantial variability was present among the patients.


CONCLUSIONS
Simulated dose accumulation might provide a more accurate depiction of the target and organ at risk coverage during fractionated whole pelvic IMRT for cervical cancer. The adequacy of primary tumor coverage using 5-mm planning target volume margins is contingent on the use of daily image-guided setup.
Radiation Medicine Program, Princess Margaret Hospital and Ontario Cancer Institute, University Health Network, Toronto, ON, Canada.
Karen
K
Lim
Valerie
V
Kelly
James
J
Stewart
Jason
J
Xie
Young-Bin
YB
Cho
Joanne
J
Moseley
Kristy
K
Brock
Anthony
A
Fyles
Anna
A
Lundin
Henrik
H
Rehbinder
Michael
M
Milosevic
D000328:Adult; D000368:Aged; D019583:Dose Fractionation, Radiation; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008875:Middle Aged; D009068:Movement; D010388:Pelvis; D011446:Prospective Studies; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D050397:Radiotherapy, Intensity-Modulated; D014057:Tomography, X-Ray Computed; D047368:Tumor Burden; D002583:Uterine Cervical Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy*