Use of CT simulation for treatment of cervical cancer to assess the adequacy of lymph node coverage of conventional pelvic fields based on bony landmarks.
OBJECTIVE
To assess the adequacy of nodal coverage of "conventional" pelvic radiation fields for carcinoma of the cervix, with contoured pelvic vessels on simulation computed tomography (CT) as surrogates for lymph node location.


METHODS
Pelvic arteries were contoured on non-contrast-enhanced CT simulation images of 43 patients with cervix cancer, FIGO Stages I-III. Vessel contours were hidden, and conventional pelvic fields were outlined: (1) anterior/posterior fields (AP): superior border, L5-S1 interspace; inferior border, obturator foramina; lateral border, 2 centimeters lateral to pelvic brim. (2) Lateral fields (LAT): Anterior border, symphysis pubis; posterior border, S2-S3 interspace. Distances were measured between the following: (1) bifurcation of the common iliac artery and superior border, (2) external iliac artery and lateral border of the AP field, and (3) external iliac artery and anterior border of the LAT field. The distances were considered as "inadequate" if <15 mm, "adequate" if 15-20 mm, and "generous" if >20 mm.


RESULTS
Superiorly, 34 patients (79.1%) had inadequate coverage. On the AP, margins were generous in 19 (44.2%), but inadequate in 9 (20.9%). On the LAT, margins were inadequate in 30 (69.8%) patients. Overall, 41 (95.4%, CI, 84.2%-99.4%) patients had at least 1 inadequate margin, the majority located superiorly. Twenty-four (55.8%; CI, 39.9%-70.9%) patients had at least 1 generous margin, the majority located laterally on the AP field.


CONCLUSIONS
Conventional pelvic fields based on bony landmarks do not provide optimal lymph node coverage in a substantial proportion of patients and may include excess normal tissue in some. CT simulation with vessel contouring as a surrogate for lymph node localization provides more precise and individualized field delineation.
Finlay
Marisa H
MH
Department of Radiation Oncology, Toronto Sunnybrook Regional Cancer Centre, Sunnybrook, Toronto, Ontario, Canada.
Ackerman
Ida
I
Tirona
Romeo G
RG
Hamilton
Paul
P
Barbera
Lisa
L
Thomas
Gillian
G
D005240:Feasibility Studies; D005260:Female; D006801:Humans; D007083:Iliac Artery / Q000000981:diagnostic imaging; D008198:Lymph Nodes / Q000000981:diagnostic imaging*; D010384:Pelvic Bones / Q000000981:diagnostic imaging; D010388:Pelvis; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D014057:Tomography, X-Ray Computed; D002583:Uterine Cervical Neoplasms / Q000098:blood supply / Q000000981:diagnostic imaging* / Q000532:radiotherapy*