Dosimetric Comparison of Sequential Boost versus Simultaneous Integrated Boost Intensity-modulated Delivery Techniques in Left-sided Breast Cancer Radiotherapy: A Planning Study

Purpose: This research compares the dosimetric characteristics of sequential boost (SB) and simultaneous integrated boost (SIB) techniques using intensity-modulated delivery techniques for breast radiotherapy in left-sided breast cancer patients following breast-conserving surgery (BCS). Materials and Methods: Twenty-seven left-sided breast cancer patients who underwent BCS were retrospectively analyzed. Two treatment plans per patient were generated using Eclipse Treatment Planning System. SB delivered 40 Gy/15 fractions (four-arc volumetric modulated arc therapy [VMAT]) to whole breast, then 12.5 Gy/5 fractions (six-field intensity-modulated radiotherapy [IMRT]) to tumor bed, totaling 52.5 Gy/20 fractions. SIB delivered 40 Gy to whole breast and 48 Gy to tumor bed simultaneously in 15 fractions through four-arc VMAT. Target coverage, dose homogeneity, conformity, and organ-at-risk doses were compared using paired t -tests ( P < 0.05). Results: Both techniques achieved adequate target coverage with comparable whole breast mean doses. SB demonstrated significantly superior V95% coverage (98.4% vs. 95.7%), while SIB significantly achieved superior dose homogeneity within the integrated plan (HI: 0.31 ± 0.025 vs. 0.14 ± 0.032). SIB showed 31% reduction in total monitor units (10669 ± 881 vs. 15450 ± 1374 MU, P < 0.001) and 25% shorter treatment duration. SIB achieved superior left anterior descending artery sparing (mean: 5.70 ± 1.78 vs. 6.54 ± 2.64 Gy, P = 0.003) and spinal cord protection (maximum: 15.3 ± 1.55 vs. 18.7 ± 4.51 Gy, P < 0.001). SB provided better ipsilateral lung sparing (mean: 11.8 ± 1.44 vs. 12.4 ± 1.04 Gy, P < 0.001). Both achieved mean heart doses <5 Gy. Conclusion: Both techniques achieved adequate target coverage, SIB offers superior treatment efficiency and coronary artery sparing, while SB provides better V95% coverage and lung sparing. Technique selection should be individualized based on patient factors and institutional priorities.