Introduction.The main aim of this study was to evaluate the doses delivered to heart substructures and calculate normal tissue complication probability (NTCP) for the intensity modulation radiotherpy (IMRT) irradiated group of left-sided post-mastectomy patients. Material and methods. In this retrospective study for 30 randomly chosen breast cancer patients, the mean dose, V2, V4, V10, V20 and D2% in the heart substructures were evaluated. Results. The mean heart dose was 12.3 Gy, the mean left anterior descending artery (LAD) dose was 28.5 Gy. The average value of long-term cardiac mortality was 0.17%, pericarditis 0.0%, left ventricle perfusion defects 24.5% and LAD toxicity 0.2%. In the literature, for the IMRT technique for left-sided mastectomy patients, the mean heart dose ranged from 8.7-14.0 Gy and the V20 10.5-14%. Additional studies are needed to describe the cardiac toxicity. Conclusions. It is necessary to contour cardiac substructures for reliable assessment of the dose distribution, although the mean heart dose is simplification for modern radiotherapy techniques.

Purpose. Bilateral postmastectomy irradiation (BPMI) poses a challenge to radiotherapists. The difficulty lies whenever targets are large, irregular and lying at different depths. When breathing movements occur it is very hard to obtain homogenous dosing on such targets and also to not exceed those doses acceptable for at-risk organs, particularly the lungs and heart. The presented study is an example of using a single isocenter Volumetric Modulated Arc Therapy (VMAT) technique for a BPMI case. Materials and methods. We report the case of a 66-year-old woman with simultaneous malignant sarcoma of the right breast and an invasive ductal carcinoma of the left breast. After modified radical mastectomy of the left breast and simple mastectomy of the right breast, the patient underwent adjuvant irradiation of the bilateral chest wall and left axillary and supraclavicular nodes region. Planning Target Volumes (PTV) and organs at risk (OAR) were delineated on CT scans. A single isocenter VMAT plan was created. The radiotherapy consisted of 50 Gy delivered in 2 Gy per fraction to the left side and 56.5 Gy delivered in 2.25 Gy per fraction to the right side in 25 fractions, five times a week over 5 weeks. Results. The left and right CTV (Clinical Target Volume) received 90% of the prescribed dose in 100% of the CTV volume. The mean heart dose was 14.4 Gy and V25 for the heart was 8.9%. The mean lung dose was 16.6 Gy and the V20 for both lungs was 28.3%. The dose to the anterior wall area of the heart was exceeded according to established constraints, but was accepted. One session of irradiation lasted about four minutes during which the patient received 595 monitor units. The treatment was carried out without interruption and complications. The early and late skin reaction was assessed as being second grade. After one year of follow-up, the patient did not present any serious side effects or recurrence. Conclusions. Synchronous irradiation of both sides of the chest wall after bilateral mastectomy with a single isocenter VMAT technique is possible and well tolerated. NOWOTWORY J Oncol 2017; 67, 1: 48-53

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