The aim of this paper is to compare the levels of radiation exposure in three variants of BC (breast cancer) exposure. The study involves dosimetric radiotherapeutic (RT) plans of 20 female patients with left BC. Pre-irradiation preparation included 3 sessions of CT scan: patient in standard dorsal position with tidal respiration (STR), in dorsal position with controlled breathhold on top inspiration (DBH) and in prone position with tidal respiration (PTR). 3D-plan dosimetric calculations were performed for three CT-sessions. Dose-volumetric measures for organs at risk (OAR) were assessed for every irradiation option. Contoured heart volume in all studied variants varied within 477 cm³ - 1056 cm³, mean volume of 769 cm³. The best values, such as V25, average doses per heart and LAD (Left arteria descending) were received using DBH method (V25 heart 4.26%, D mean heart 3.13 Gy, DmeanLAD 13.8 Gy) as compared to STR method (V25 heart 9,49%, D mean heart 4.97Gy, DmeanLAD 19.55Gy) and PTR-position (V25 heart 12,8%, Dmean heart 9.06Gy, DmeanLAD 24.18Gy) (V25 heart P = 0.00153, D mean heart: P =0.000; D mean LAD: P = 0.00088), with the inclusion of Mamma Glandule (MG) and axillary LN in the total volume. The preferences of STR- and DBH-related dosimetric values remained unchanged followed by the inclusion of supraclavicular and infraclavicular lymph nodes (LN) in the total volume. DBH method (V25 heart 3.49%, D mean heart 3.07Gy, DmeanLAD 13.88Gy) was compared to STR method (V25 heart 7.91%, D mean heart 4.99 Gy, DmeanLAD 19.89Gy) (V25 heart P = 0.00205, D mean heart: P =0.004; D mean LAD: P = 0.03). Irradiation in dorsal position was performed with controlled breath hold while full inspiration was associated with a statistically significant decrease of the heart volume, which was exposed to more than 25 Gy (V25heart), average heart dose, average LAD dose.

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