Radiobiological evaluation of hypofractionated vs conventional VMAT for synchronous bilateral breast cancer: a focus on regional nodal irradiation
Authors: Md Rashidul Islam¹*, Samiul Hasan Shovon¹, Md Mokhlesur Rahman²
Institution: Gono Bishwabidyalay (University)
Introduction
To compare the radiobiological characteristics of hypofractionated radiotherapy (HFRT) and conventional fractionated radiotherapy (CFRT) delivered with volumetric modulated arc therapy (VMAT) for synchronous bilateral breast cancer (SBBC) requiring regional nodal irradiation (RNI).
Methods
Eighteen patients with SBBC receiving bilateral breast/chest wall irradiation and comprehensive nodal coverage were retrospectively included. For each patient, VMAT plans were generated for CFRT (50 Gy in 25 fractions) and HFRT (40.05 Gy in 15 fractions). Dosimetric parameters of the planning target volume (PTV) were evaluated. Radiobiological assessment included equivalent uniform dose (EUD), tumor control probability (TCP), and normal tissue complication probability (NTCP). TCP was calculated using LQ-Poisson and Niemierko models, while NTCP for the lungs, heart, spinal cord, and esophagus was estimated using Lyman Kutcher Burman and Niemierko models.
Results
Both regimens achieved excellent target coverage, with mean PTV V₉₅% values exceeding 99%. HFRT significantly reduced high-dose regions within the PTV, as reflected by lower V₁₀₇% values (median: 1.35% vs. 2.60%; IQR: 5.75% vs. 7.85%; P < 0.001). PTV EUD was significantly lower with HFRT than with CFRT (median: 45.69 vs. 51.34 Gy; P < 0.001). Although TCP values were lower with HFRT in both models, tumor control remained high for both schedules. HFRT also significantly reduced EUD and NTCP values for the lungs, heart, and esophagus, whereas no significant differences were observed for the spinal cord.
Conclusion
For SBBC patients requiring RNI, HFRT-VMAT achieved target coverage comparable to CFRT while reducing excessive high-dose regions and predicted toxicity to major thoracic organs. Despite slightly lower TCP values, overall tumor control remained favorable, supporting HFRT-VMAT as a feasible treatment option for this patient population.
