A Comparative Analysis of the Conventional Pelvic Fields Based on Bony Landmarks and Contrast-Enhanced CT Simulation for the Treatment of Cervical Cancer

To compare and assess the adequacy of treatment volume coverage of “conventional” pelvic radiation fields based on bony landmarks with 3D conformal simulation based on contrast-enhanced CT for radical radiotherapy of the uterine cervix carcinoma. Gross, clinical and planning target volumes (GTV, CTV, PTV), as well as OAR (bladder, rectum and bowel), were contoured on contrast-enhanced CT simulation images of 20 patients with cervix cancer, FIGO Stages I–III (1 Ib2, 5 IIB e 14 IIIB). Three dimensional dose distribution of CT–based treatment plan was compared to the 3D dose distribution derived from a four-field-box-technique using standard portals based on bony landmarks: (1) anterior/posterior fields: superior border, L5–S1 (FIGO stage I–II) or L4–L5 (FIGO stage IIB and III) interspace; inferior border, obturator foramina; lateral border, 2 centimeters lateral to pelvic brim. (2) Lateral fields: anterior border, symphysis pubis; posterior border, S2–S3 interspace. The adequacy of the conventional fields was assessed through the DRRs, and dose distribution in the target volumes and in the OAR was compared between the two plans using dose-volume histograms. 19/20 (95%) of the conventional plans were considered inadequate, with the PTV receiving less than 95% of the prescribed dose (according to ICRU 62), and in 15 (75%) less than 95% of the PTV received 4275 cGy. 14 (70%) patients had inadequacies at least in one field: 12 in the lateral field, and 2 in the AP-PA and lateral fields. Five cases (25%) would have a geographic miss in the PTV at the uterine cervix plus 1 cm margin (four of these in the GTV itself); and in 60% the common iliac lymph nodes were not covered in the conventional fields. There was a significant increase in the maximum dose received by the OAR, the volume of bowel receiving 30 Gy, and a decrease in the bladder volume receiving 95% of the prescribed dose in the 3D plans. Six cases had inadequate plans just for the prescribed isodose (100%) in the conventional planning. Conventional pelvic fields based on bony landmarks do not provide adequate treatment volume coverage in a substantial proportion of patients. CT simulation provides more precise and individualized field delineation. Whenever possible, individualized treatments fields based on CT or MRI should be employed.