Aim of the study. The aim of this study was to compare the IMRT (Intensity Modulated Radiation Therapy) and 3D-CRT (3-Dimensional Conformal Radiation Therapy) techniques as far as the planning target volume (PTV) coverage and normal tissue sparing in concerned.

Material and methods. IMRT and 3D-CRT plans for 15 patients with early breast cancer after breast conservation therapy were prepared with the Eclipse treatment planning system. For plan comparison in PTVbreast and in PTVnodes the minimal dose — Dmin, maximal dose — Dmax, standard deviation — SD, and Coverage Index — CovI were evaluated. For organs at risk (both lungs, heart, coronary arteries and healthy breast) during preparation of 3D-CRT and IMRT plans dose volume constrains were established.

Results. In the group of patients with left breast cancer only, without involved lymph nodes, lower SD values (mean 0.8%) and higher values of CovI (mean 0.03) were obtained for IMRT technique. In the group of patients requiring supraclaviculary and axillary lymph nodes irradiation, a lower value of SD 1.3% vs 4.4% for left side and 1.4% vs 5.0% for right side were obtained for IMRT. In the IMRT technique a higher value of CovI 0.99, independent of the irradiated side, were obtained as compared to 0.55 for left side and 0.39 for right side in the 3D-CRT. The 3D-CRT technique offers more sparing to organs at risk in comparison with coplanar fields in IMRT. In the group of patients without irradiated lymph nodes, the mean heart volume receiving 20 Gy or more was lower in 3D-CRT — 0.2% compared to 2.6% in IMRT. For coronary arteries Dmax — was 33.7 Gy in IMRT vs 37.5 Gy in 3D-CRT, Dmean in IMRT — was 9.1 Gy vs 3.2 Gy w 3D-CRT. Mean volume of lung on irradiated side receiving dose of 20 Gy was 20% in IMRT and 7.4% in 3D-CRT. Mean value of Dmean in right lung was 14.7 Gy in IMRT vs 4.8 Gy in 3D-CRT. In the group of patients with irradiated breast and lymph nodes on the left side the mean Dmax in coronary arteries is 7 Gy lower and the Dmean is 5 Gy higher in the IMRT technique. The volumes of lung on the irradiated side receiving a dose of 20 Gy were similar in both techniques — 27.3% in IMRT vs 26.3% in 3D-CRT. Dmean for lung on irradiated side was 5 Gy higher in the IMRT. The Dmean doses for right lung and right breast were 5.9 Gy and 4.6 Gy in the IMRT compared to 0.8 Gy and 0.7 Gy in the 3D-CRT.

Conclusions. Dose distributions in both techniques for patients with left side breast only were similar. The differences were observed for patients with involved lymph nodes, regardless of the side of involved breast. Conventional breast irradiation 3D-CRT was better for sparing of normal tissue. However, the constraints for the organs at risk for the IMRT were also fulfilled.