Introduction: The aim of radiotherapy (Rth) is to provide optimal dose to the 
target with the least dose to surrounding risk structures. Intensity-modulated 
radiation therapy (IMRT) intends to improve the reach of optimal dose 
conformity to the target with the least risk structure dose. The aim of the study 
is to compare dose to the target and risk structures using (IMRT) and 3D 
conformal radiotherapy (3DCRT) for adjuvant left breast cancer.
Methods: This study included 20 localized unilateral breast cancer patients 
treated for adjuvant 3DCRT in the Aswan Cancer Centre. The treatment was 
planned for 3DCRT and then another plan for IMRT later on for the purpose of 
this dosimetric study. We compared both plans for target structure coverage, 
risk structure, and number of monitor units.
Results: PTV total V95% was significantly better for IMRT vs. 3DCRT 
(92.2%) vs. 88% (p = 0.025). The conformity index was also significantly 
superior for IMRT planning. The other parameters for PTV total coverage and 
homogeneity index showed no significant difference between both techniques.
IMRT insignificantly reduced the mean heart dose, 2.6 Gy for IMRT vs. 3.2 Gy 
for conformal (p = 0.368). It was also observed that the IMRT plans achieved a 
lower left lung dose than the conformal ones, i.e., 7.7 Gy vs. 7.9 Gy (p = 0.38). 
Contralateral breast mean and D5 doses were significantly lower in favour of 
3DCRT vs IMRT (0.7 vs. 1.1 and 0.1 vs. 0.8; P values =0.01 and 0.043) 
respectively.
Conclusion: Overall, IMRT achieved superior dose parameters and marginally 
better risk structures sparing than 3D-CRT. However, contralateral breast mean 
and D5 doses were significantly better in favour of conformal planning.