Comparative Dosimetric Analysis of Three Radiotherapy Fractionation Schedules in Synchronous Bilateral Breast Cancer:...

This study aims to evaluate and compare the impact of dosimetric parameters on lungs, heart, and associated normal tissue complication probability (NTCP) values among three different right (RT) prescription doses in patients with synchronous bilateral breast cancer (SBBC).

For retrospectively selected five patients diagnosed with SBBC, volumetric-modulated arc therapy treatment plans were developed across three different fractionation schedules: ultra-hypofractionated (UHF) (26 Gy/5#), hypofractionated (HF) (40.05 Gy/15#), and conventional fractionation (CF) (50 Gy/25#). The dosimetric parameters, including conformity index (CI), coverage index, homogeneity index, D95%, and V105%, along with the doses to organ at risk (OAR) (lung, heart, left anterior descending artery), were assessed. NTCP models were used to estimate the risks of complications.

The dose-volume parameters for OAR exhibited a parabolic trend (χ²) with the prescribed dose, showing significant statistical differences across various fractionation schedules (P = 0.985, P < 0.001). NTCP models indicated a reduction in risks with UHF compared to CF and HF, with probabilities of grade ≥2 radiation pneumonitis ranging from 2.69% to 6.80% and symptomatic fibrosis probabilities from 22.45% to 38.91%, both of which increased from UHF to CF. The calculations for biological effective dose and equivalent dose in 2 Gy fractions showed greater biological effectiveness for late-responding tissues in CF, while the impact on tumor control remained more uniform across different fractionation schemes.

This study provides evidence in favor of hypofractionation for breast cancer radiotherapy, showing promise in minimizing normal tissue side effects.