Purpose: The emergent use of combined modality approach (chemotherapy and radiation therapy) for the treatment of patients with cervical cancer is associated with significant gastrointestinal and genitourinary toxicity. Intensity-modulated radiation therapy (IMRT) has the potential to deliver adequate dose to the target structures while sparing the normal organs and could also allow for dose escalation to grossly enlarged metastatic lymph node in pelvic or para-aortic area without increasing gastrointestinal/genitourinary complications. We conducted a dosimetric analysis to determine if IMRT can meet these objectives in the treatment of cervical cancer.
Methods and materials: Computed tomography scan studies of 10 patients with cervical cancer were retrieved and used as anatomic references for planning. Upon the completion of target and critical structure delineation, the imaging and contour data were transferred to both an IMRT planning system (Corvus, Nomos) and a three-dimensional planning system (Focus, CMS) on which IMRT as well as conventional planning with two- and four-field techniques were derived. Treatment planning was done on these two systems with uniform prescription, 45 Gy in 25 fractions to the uterus, the cervix, and the pelvic and para-aortic lymph nodes. Normalization was done to all IMRT plans to obtain a full coverage of the cervix with the 95% isodose curve. Dose-volume histograms were obtained for all the plans. A Student's t test was performed to compute the statistical significance.
Results: The volume of small bowel receiving the prescribed dose (45 Gy) with IMRT technique was as follows: four fields, 11.01 +/- 5.67%; seven fields, 15.05 +/- 6.76%; and nine fields, 13.56 +/- 5.30%. These were all significantly better than with two-field (35.58 +/- 13.84%) and four-field (34.24 +/- 17.82%) conventional techniques (p < 0.05). The fraction of rectal volume receiving a dose greater than the prescribed dose was as follows: four fields, 8.55 +/- 4.64%; seven fields, 6.37 +/- 5.19%; nine fields, 3.34 +/- 3.0%; in contrast to 84.01 +/- 18.37% with two-field and 46.37 +/- 24.97% with four-field conventional technique (p < 0.001). The fractional volume of bladder receiving the prescribed dose and higher was as follows: four fields, 30.29 +/- 4.64%; seven fields, 31.66 +/- 8.26%; and nine fields, 26.91 +/- 5.57%. It was significantly worse with the two-field (92.89 +/- 35.26%) and with the four-field (60.48 +/- 31.80%) techniques (p < 0.05).
Conclusion: In this dosimetric study, we demonstrated that with similar target coverage, normal tissue sparing is superior with IMRT in the treatment of cervical cancer.