For postmastectomy radiation therapy (PMRT), it is extremely important that the chest wall skin receives adequate dose. The aim of this prospective study was to evaluate the effect of bolus in breast cancer patients treated with 3D conformal radiotherapy (3D-CRT) and intensity-modulated radiotherapy (IMRT) techniques by in vivo dosimetry. The study included 20 mastectomized breast cancer patients. Nine different points were marked on the chest wall surface of the patients before computed tomography (CT). It was ensured that the dose reading points were the same in treatment planning system (TPS) and in-vivo measurements. Half of the patients in the study group were treated with IMRT and the other half with 3D-CRT technique. 3D-CRT and IMRT patients were planned to be treated with bolus every other day. Dose distributions for the presence and absence of bolus were obtained from the chest wall skin of each patient. In in-vivo dose measurements in IMRT patients, the mean skin dose without bolus was 152.06 cGy, while the mean skin dose increased to 213.95 cGy with the use of bolus. In the 3D-CRT technique, the mean chest wall dose in TPS was 146.78 cGy and 201.1 cGy for non-bolus and bolus plans, respectively. For both treatment techniques, the skin dose calculated by TPS was lower than in-vivo dose measurements. In this study, it was observed that the use of bolus increased the skin dose sufficiently. It was also observed that skin doses were more homogeneous in 3D-CRT technique than IMRT technique. It was observed that TPS has significant deficiencies in dose calculation in the evaluation of skin doses in breast radiotherapy, therefore, it is recommended to use in-vivo dosimetric methods for control.