INTRODUCTION: Pectus excavatum is a frequent anomaly. It represents a challenge for adjuvant radiotherapy in the conservative treatment of breast cancer. Primary objective of this study is to compare dosimetric outcomes, normal tissue complication probability (NTCP), and integral dose using four radiation techniques. Secondary objective is to describe acute toxicity and setup errors. METHODS AND MATERIALS: A 57-year-old female patient with an inner quadrant, left breast, ductal carcinoma in situ, was identified. Whole breast was prescribed with 50 Gy in 25 fractions. Boost planning target volume (PTV) was prescribed with 60 Gy in 30 fractions for sequential boost (SB) plans or 57.5 Gy in 25 fractions in the simultaneous integrated boost (SIB) plan. All plans were normalized to deliver 47.5 Gy to 95 % of the breast PTV. Daily image-guided radiotherapy (IGRT) was performed. Setup deviations were described. RESULTS: Constraints were not accomplished for heart when using intensity modulated radiotherapy (IMRT) + SB or conformal radiotherapy with three photon fields and SB. Left lung constraint was not achieved by any of the techniques in comparison. IMRT + SIB and conformal photons and electrons + SB plan were closer to the objective. Integral doses were lower with IMRT for heart and ipsilateral lung; however, it were higher for contralateral breast and lung. Coverage and tumoral conformity indexes were similar for all techniques in comparison. Greater inhomogeneity was observed with the photons and electrons + SB. IMRT + SIB treatment was administered daily with grade I skin toxicity. The highest setup error was observed in Y direction. CONCLUSION: Planning target volume coverage was similar with the four techniques. Homogeneity was superior with both IMRT plans. A good balance between dose constraints for organs at risk, PTV coverage, homogeneity, and NTCP was observed with IMRT + SIB. The documented daily setup error justifies the use of online IGRT.