Background: Breast cancer is one of the most prevalent cancers among women. 
The objective of this research is to compare adjuvant Rapid Arc radiotherapy 
with conventional modality in respect of dose distribution in target volume and 
critical organs in patients with breast cancer post-surgery.
Patients and Methods: This prospective research enrolled 98 cases diagnosed 
with primary breast cancer post conservative or mastectomy surgery recruited 
from Clinical Oncology Department, Zagazig University and International 
Medical Center, Egypt between January 2021-December 2022. They were 
categorized into 2 groups; group A underwent therapy by 3D-Conformal 
Radiotherapy (3DCRT) whereas group B was managed by Rapid Arc 
radiotherapy (RA). Both groups received 50 Gy in 25 fractions. 
Results: Each group had 49 patients. Both plans achieved similar target 
coverage; however RA had significantly increasing in minimum dose to the 
target more than 3D (66.21% vs 28.86%, p=0.001), moreover the Homogeneity 
Index (HI) & Conformity Index (CI) of RA were better than 3D-CRT (HI 1.05 
vs 1.2, p=0.08 and CI 0.76 vs 0.38, p=0.034). Both plans had comparable results 
regarding to mean heart dose, V25 of heart, mean lung dose, V20 of ipsilateral 
lung and contralateral lung dose, however; 3D-CRT had better sparing in case of 
V5 & V10 of heart, V10 of ipsilateral lung and contralateral breast dose. 
Conclusion: Both RA & 3D-CRT have similar target coverage; however RA 
had better CI & HI at the expense of organs at risk sparing so RA may be used 
in sophisticated cases for whom optimal target coverage cannot be achieved by 
3D-CRT.