Three-dimensional treatment planning for postoperative radiotherapy in patients with node-positive cervical cancer - Comparison between a conventional and a conformal technique
Mjj. Olofsen-van Acht et al., Three-dimensional treatment planning for postoperative radiotherapy in patients with node-positive cervical cancer - Comparison between a conventional and a conformal technique, STRAH ONKOL, 175(9), 1999, pp. 462-469
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.