Purpose Synchronous bilateral irradiation of both mammary glands and chest wall is a challenging task due to technical difficulties and limited evidence supporting an optimal technique to improve treatment outcomes. We studied and compared the dosimetry data of three radiotherapy techniques to select the most optimal one. Methods We compared three-dimensional conformal radiation treatment (3D CRT), intensity-modulated radiation therapy (IMRT), and volumetric modulated arc therapy (VMAT) during irradiation of synchronous bilateral breast cancer in nine patients followed by examination of dose distribution to the cardiac conduction system (SA node, AV node and Bundle of His), myocardium, lungs, left anterior descending artery (LADA) and right coronary artery (RCA) . Results VMAT is the most sparing technique for SBBC treatment. Even though doses to the SA node, AV node and Bundle of His were higher with VMAT (Dmean were 3.75 ± 0.62, 2.58 ± 0.83 and 3.03 ± 1.18 Gy respectively) compared with 3D CRT (Dmean were 2.61 ± 0.66, 1.52 ± 0.38 and 1.88 ± 0.70 Gy respectively), this difference is statistically insignificant. Doses to the right and left lung (average Dmean = 12.65 ± 3.20 Gy, V20Gy = 24.12 ± 6.25%), myocardium (Dmean = 5.33 ± 1.51 Gy, V10Gy = 9.80 ± 3.83%, V20Gy = 7.19 ± 3.15%, V25Gy = 6.20 ± 2.93%), and LADA (Dmean = 10.04 ± 4.92 Gy, V20Gy = 18.17 ± 13.24% and V25Gy = 15.41 ± 12.19%) were highest with 3D CRT. The highest  Dmean in the cardiac conduction system (5.30 ± 2.23, 3.15 ± 1.61 and 3.89 ± 1.85 Gy respectively) was observed with IMRT, and a similar effect was noted in RCA (Dmean = 7.48 ± 2.11 Gy). Conclusion VMAT is the optimal and satisfactory radiation therapy technique for sparing organs at risk (OARs). With VMAT, a lower Dmean value was noted in the myocardium, LADA, and lungs. The use of 3D CRT significantly increases the dose of radiation reaching the lungs, myocardium, and LADA, which can subsequently cause cardiovascular and lung complications, but not in the cardiac conduction system.

Тему лучевого лечения рака молочной железы (РМЖ) не перестают обсуждать на научных съездах и страницах онкологических журналов. Это понятно, ведь облучение, как и хирургическая операция, высокоэффективная и до сих пор неотъемлемая часть противоракового лечения. Лечение ионизирующим излучением в различных вариантах используется при РМЖ от нулевой (TisN0M0) до IV стадии. Лечение РМЖ имеет более чем вековую историю. С него началось использование ионизирующего излучения в лечебных целях. Первый сеанс лечения РМЖ провел Эмиль Груббей (Emil Grubbe) в 1896 г. в Чикаго, о чем он написал в журнале «Radiology» в 1933 г. [1], но до сих пор мы обсуждаем, какова должна быть мишень у тех или иных больных, какая методика облучения для них более всего подходит и какой режим фракционирования наиболее успешен. Эти направления поддерживаются сохраняющимся высоким уровнем заболеваемости и смертности от РМЖ и высокой социальной значимостью болезни. В онкологической среде нет необходимости говорить о важности лучевого компонента в лечении, однако в менее специализированных учреждениях его нередко недооценивают как врачилечебники, так и врачи-администраторы. Это приводит к ошибкам в составлении планов комбинированного и комплексного

medical Academy of Postgraduate Education, ministry of Health of the Russian Federation, moscow, RussiaThe paper presents basic radiobiological models in radiation oncology as the theories that predict the effect in normal tissues and in tumors during their ionizing radiation. It shows their mathematical basis leaning upon an event in a certain cell, as well as they are applied to the practice of radiation therapy to calculate the dose of radiation and the number of fractions per treatment cycle in order to adjust the dose sufficient for tumor destruction, by preserving the viability or physiological function of normal tissues and organs. The paper considers how the radiobiological models allow one to compare the biological effect of irradiation in a variety of dose adjustment over time, i.e. during different fractionation modes and how they are used to represent physical quantities (e.g. an absorbed dose) as clinical indicators, such as a biologically effective dose, tumor control probability, and normal tissue complication probability, which are used to optimize radiation plans. It gives the history of radiobiological models and the current view on their role in the practice of radiotherapy.

Purpose: Synchronous bilateral irradiation of both the mammary glands and the chest wall is a challenging task due to technical difficulties and limited evidence supporting an optimal technique for positive treatment outcomes. We analyzed and compared the dosimetry data of three radiotherapy techniques and selected the most effective one.Methods: Three-dimensional conformal radiation treatment (3DCRT), intensity-modulated radiation therapy (IMRT), and volumetric-modulated arc therapy (VMAT) were compared during the irradiation of synchronous bilateral breast cancer. This was followed by examination of the dose distribution to the target organs (myocardium, left anterior descending artery (LADA), right coronary artery (RCA), and lungs in nine patients.Results: Dose distribution in the lungs was optimal using VMAT, while IMRT was less effective. Doses in the lungs, myocardium, and LADA were highest with 3DCRT. The highest mean dose in the myocardium was observed with IMRT, and a similar effect was noted with RCA. VMAT is the most sparing technique for the myocardium and LADA, despite the RCA dose being slightly higher when compared with that of 3DCRT.Conclusion: We concluded that VMAT is a very effective and satisfactory radiation technique for sparing critical organs. With VMAT, regardless of the volume and side of irradiation, a lower mean dose (Dmean) value was noted in organs at risk such as the myocardium, LADA, and lungs, but not the cardiac conduction system. The use of 3DCRT significantly increases the dose of ionizing radiation reaching the lungs, myocardium, and LADA, which can subsequently cause cardiovascular and lung complications.