UICC World Cancer Congress 2006

Radiotherapy plays an important role in breast cancer. In this study, the optimum number of CT slices required for planning breast cancer by tangential field technique has been assessed by comparing the treatment plans according ICRU 50 guidelines for single- slice, three-slice and multi-slice planning.

Methods:

Sixty patients were selected for this study and CT scanning was done for all the patients. Separate tangential field plans were made for single-slice planning; three-slice planning and complete 3D based planning. The dose was prescribed and normalized to the isocentre. The single-slice plan and three-slice plan were exported to the complete 3D CT image datasets and the dose was re calculated without any change in the beam parameters. The PTV receiving <95% and >107% were noted down for all the three compared as per ICRU 50 guidelines (1993).

Results:

63.3% of the single-slice plan and 26.7% of the 3 slice plan showed poor dose homogeneity when compared to the 3D plans, these patients would have achieved a better dose homogeneity if they would have been planned using full set of CT slices. The dose inhomogeneity correlated with the breast volume (r=0.66). Our study revealed that single-slice planning is unsuitable in most of the cases and planning on three slices can be performed for most of the cases except for large breast where 3D treatment planning is mandatory. Hence, in situations where there is no complete CT slice available for planning, a minimum of 3 slices should be used for planning.