Aim: Dose calculation algorithms play a pivotal role in assessing normal tissue 
toxicity and treatment outcomes during radiotherapy planning. Therefore, this 
study aimed to evaluate the Acuros External Beam (AXB) algorithm and 
Anisotropic Analytical Algorithm (AAA) for radiotherapy planning of left-sided 
breast cancer treatment with the UK FAST trial.
Methods: A total of 100 treatment plans were retrospectively calculated with 
AAA and AXB algorithm for 50 patients with left-sided breast cancer at an 
early stage who received treatment with the UK FAST trial. The field angle, 
geometry, energy, beam segments, and prescription point were kept the same to 
avoid any bias when comparing algorithms.
Results: The planning target volume (PTV) coverage parameters for AXB plans 
were higher than those for AAA plans, with a statistically significant difference 
in V90%, V105% and V107% between both calculation algorithms (p < 0.05). 
When comparing AXB with AAA calculated plans for the heart dosimetric 
parameters, the heart V25% for the AXB increased significantly, while the heart 
V5% was lower. The ipsilateral lung V30% and V15% of the AXB plans were 
significantly greater than those of the AAA plans. In contrast, the ipsilateral 
lung V5% decreased significantly. The AXB plans had a significantly increased 
average of 3% of the contralateral breast volume.
Conclusion: It is important to use the efficient AXB algorithm to better 
estimate normal tissue toxicity and treatment outcomes in the treatment of breast 
cancer using the UK FAST trial.