Comparison of CT-based 3D treatment planning with simulator planning of pelvic irradiation of primary cervical carcinoma

Background: Using standardized simulator planning guided by bony landmarks for pelvic irradiation of primary cervical carcinoma with some patients a geographical miss regarding tumor or potential tumorspread can happen because of insufficient knowledge of the individual anatomical situation. The question arises whether for patients with this indication the higher effort in terms of time and personnel for 3D treatment planning is justified. Patients and Method: In a prospective study on 20 subsequent patients with primary cervical carcinoma in Stages I to III simulator planning of a 4-field box-technique was performed. After defining the planning target Volume (PTV) in the 3D planning system the field configuration of the simulator planning was transmitted. The resulting plan was compared to a second one based on the defined PTV and evaluated regarding a possible geographical miss and encompassment of the PTV by the treated volume (ICRU). Volumes of open and shaped portals were calculated for both techniques. Results: Planning by simulation resulted in 1 geographical miss and in 10 more cases the encompassment of the PTV by the treated volume was inadequate. For a PTV of mean 1 729 cm(3) the mean volume defined by simulation was 3 120 cm(3) for the open portals and 2 702 cm(3) for the shaped portals (Figure 1). The volume reduction by blocks was 13.4% (mean). With CT-based 3D treatment planning the volume of the open portals was 3.3% (mean) enlarged to 3 224 cm(3) (Figure 2). The resulting mean volume of the shaped portals was 2 458 ccm. The reduction compared to the open portals was 23.8% (mean). The treated volumes were 244 cm(3) or 9% (mean) smaller compared to simulator planning. The "treated volume/planning target volume ratio" was decreased from 1.59 to 1.42. Conclusion: The introduction of 3D treatment planning for pelvic irradiation of cervical carcinoma is to be recommended for reasons of quality assurance. Reduction of the treated volume is possible but further research has to be done to determine whether the rate of complications can be decreased as well.