We present evaluation of junction of coplanar external beam photon fields and its
portal dosimetric analysis for breast cancer with positive lymph nodes. In our work,
we compared twelve patients affected by breast cancer with axillary and supraclavicular
lymph nodes, using conformal external beam plans from a dosimetric point of view.
3-3 plans were prepared per patient. Three methods were used for the conformal technique
to investigate the potential of lymph nodes treatment field's collimations. During
the evaluation of the portal dosimetry images, it was concluded that the junction
plane at isocenter appeared as a discrete coldline, when fitted the regional field
with or without collimation manually and by the software. However, the coverage of
the isocenter plane is strongly influenced by the linear accelerator and the fitted
field edges. Based on our results, in order to avoid uncertainties arising from field
junctions and the overdosed areas of the target volume, it is more appropriate to
choose another advanced irradiation technique such as intensity-modulated radiation
therapy.
