We evaluated whether the field-in-field (FIF) technique improves the homogeneity of the target in high tangent radiation therapy (HTRT).


 In total, 3 HTRT plans were created: 1 with conventional opposed fields (Conv-p), 1 with the FIF technique (FIF-p), and 1 with FIF technique using lung-blocked subfields (FIF-LB-p).


 The FIF technique was useful in HTRT and improved homogeneity in the target.
HTRT
We evaluated whether the field-in-field (FIF) technique improves the homogeneity of the target in high tangent radiation therapy (HTRT).


 In total, 3 HTRT plans were created: 1 with conventional opposed fields (Conv-p), 1 with the FIF technique (FIF-p), and 1 with FIF technique using lung-blocked subfields (FIF-LB-p).


 The maximum dose of the breast and planning target volume (PTV) was significantly lower for FIF-p and FIF-LB-p than Conv-p.  Homogeneity index of PTV was also significantly lower for FIF-p and FIF-LB-p than Conv-p.  Homogeneity index of the breast or PTV was significantly better for FIF-p than FIF-LB-p.  The volumes of the breast or the PTV receiving 95% and 90% of the prescribed dose were also significantly better for FIF-p, indicating the advantages of FIF-p.


 The FIF technique was useful in HTRT and improved homogeneity in the target.
FIF
In total, 3 HTRT plans were created: 1 with conventional opposed fields (Conv-p), 1 with the FIF technique (FIF-p), and 1 with FIF technique using lung-blocked subfields (FIF-LB-p).


 The maximum dose of the breast and planning target volume (PTV) was significantly lower for FIF-p and FIF-LB-p than Conv-p.  Homogeneity index of PTV was also significantly lower for FIF-p and FIF-LB-p than Conv-p.  Homogeneity index of the breast or PTV was significantly better for FIF-p than FIF-LB-p. 
FIF-LB