Intensity-modulated radiation therapy (IMRT) reduces small bowel, rectum, and bladder doses in patients with cervical cancer receiving pelvic and para-aortic irradiation

Purpose: The emergent use of combined modality approach (chemotherapy and r adiation therapy) for the treatment of patients with cervical cancer is ass ociated with significant gastrointestinal and genitourinary toxicity. Inten sity-modulated radiation therapy (IMRT) has the potential to deliver adequa te 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/genitourina ry complications. We conducted a dosimetric analysis to determine if IMRT c an 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 plannin g. Upon the completion of target and critical structure delineation, the im aging and contour data were transferred to both an IMRT planning system (Co rvus, Nomos) and a three-dimensional planning system (Focus, CMS) on which IMRT as well as conventional planning with two- and four-field techniques w ere derived. Treatment planning was done on these two systems with uniform prescription, 45 Gy in 25 fractions to the uterus, the cervix, and the pelv ic 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-volu me histograms were obtained for all the plans. A Student's t test was perfo rmed to compute the statistical significance. Results: The volume of small bowel receiving the prescribed dose (45 Gy) wi th IMRT technique was as follows: four fields, 11.01 +/- 5.67%; seven field s, 15.05 +/- 6.76%; and nine fields, 13.56 +/- 5.30%. These were all signif icantly 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 fiel ds, 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 bl adder 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%) an d with the four-field (60.48 +/- 31.80%) techniques (p < 0.05). Conclusion: In this dosimetric study, we demonstrated that with similar tar get coverage, normal tissue sparing is superior with IMRT in the treatment of cervical cancer. (C) 2001 Elsevier Science Inc.