Three-dimensional treatment planning for postoperative radiotherapy in patients with node-positive cervical cancer - Comparison between a conventional and a conformal technique

Purpose: Reduction of irradiated small bowel volume, using a conformal thre e-dimensional treatment planning technique in postoperative radiotherapy of cervical cancer patients. Patients and Methods: Large gynecological treatment fields including the pa ra-aortic nodes were analyzed in 15 patients. A conventional treatment plan with anterior and posterior (AP-PA) parallel opposed fields and a 3D 4-fie ld conformal radiotherapy plan with a central blocking of small bowel were compared for each patient. Dose-volume histograms and dose parameters were established. Because of the tolerance constraints of the small bowel, the c umulative dose applied to the target was 48.6 Gy. Results: The mean Tumor Control Probability (TCP) values for both the conve ntional and the conformal technique were 0.60 and 0.61, respectively, with ranges of 0.56 to 0.67 and 0.57 to 0.66, respectively. The mean volume rece iving 95% or more of the prescribed dose (V95) of the small bowel was 47.6% (32.5 to 66.3%) in the AP-PA technique and 14.9% (7.0 to 22.5%) in the con formal technique (p < 0.001), indicating a significant reduction in irradia ted volume of small bowel in the higher dose range. The mean Normal Tissue Complication Probability (NTCP) decreased from 0.11 to 0.03 with the confor mal plan. In patients who received a pedicled omentoplasty during surgery, the mean V95 for small bowel could be reduced to 8.5% (7.0 to 9.9%). The me an median dose to the kidneys was only slightly elevated in the conformal t reatment. Especially the mean dose to the right kidney in conventional vs c onformal treatment was 3.3 vs 7.9 Gy. The mean near-minimum dose (D95) to t he rectosigmoid decreased from 48.4 to 30.1 Gy in the conformal plan compar ed to the conventional plan. Conclusion: The small bowel dose can be significantly reduced with 3D treat ment planning, particularly if a pedicled omentoplasty is performed. This a llows dose escalation to the tumor region without unacceptable toxicity for the small bowel.