Low dose out-of-field radiotherapy, part 3: Qualitative and quantitative impact of scattered out-of-field radiation on MDA-MB-231 cell lines

• Published in: Cancer radiothérapie 2017-08, Vol.21 (5), p.358-364
• Main Authors: Zaleska, K., Suchorska, W.M., Kowalik, A., Kruszyna, M., Jackowiak, W., Skrobala, A., Skorska, M., Malicki, J.
• Format: Article
• Language: English
• Subjects: Breast Neoplasms - genetics; Breast Neoplasms - pathology; Breast Neoplasms - radiotherapy; Cell Line, Tumor; Cell survival; Cell Survival - radiation effects; Des cassures double-brin; DNA Damage; Double strand-breaks; Hors champ de rayonnement; Humans; La survie des cellules; Out-of-field radiation; Radiotherapy Dosage; Rayonnement diffusé; Scattered radiation
• ISSN: 1278-3218; 1769-6658
• DOI: 10.1016/j.canrad.2016.04.008

Patients who undergo external beam radiotherapy are at risk of developing second tumours due to scattered radiation outside the path of the primary beam. The aim of this study was to experimentally determine the in vitro radiobiological effects of scattered radiation in cells located outside the primary photon beam and to compare this to the effects that occur in cells inside the primary beam. The comparison was performed by assessing cell viability, DNA damage, and apoptosis. Cells from the human breast cancer line MDA-MB-231 were inserted in a water phantom and irradiated at varying doses (1.5, 2.0, 2.5, and 3.0Gy). The cells were placed at two geometrical points: in the central beam axis and at 10cm out-of-field. The dose was constant in both geometrical points. Survival fraction, number of DNA double strand-breaks, and cleaved poly-(ADP-ribose) polymerase (PARP) levels were determined by clonogenic assay and flow cytometry. A slight, non-significant decrease of 3 to 5% in cell survival fraction was observed in cells irradiated outside the primary field. The number of PARP-positive cells and DNA double strand-breaks both increased after out-of-field irradiation. Scattered irradiation appears to induce an in vitro biological response on out-of-field cells that is stronger than the effect of primary radiation on in-field cells, independent of the bystander effect. These findings suggest that the biological response of healthy tissues outside the primary beam might be higher than previously believed. Les patients qui reçoivent une radiothérapie externe sont à risque de voir se développer des tumeurs secondaires dues au rayonnement diffusé en dehors du trajet du faisceau primaire. L’objectif de cette étude était de déterminer expérimentalement les effets radiobiologiques in vitro du rayonnement diffusé dans les cellules situées en dehors du faisceau de photons primaires et de les comparer à ceux qui se produisent dans les cellules situeés à l’intérieur du faisceau primaire. La comparaison a été effectuée en évaluant la viabilité des cellules, des lésions de l’ADN et l’apoptose. Des cellules de la lignée de cancer du sein humain MDA-MB-231 ont été insérées dans un fantôme d’eau et irradiées à diverses doses (1,5, 2,0, 2,5 et 3,0Gy). Les cellules ont été placées en deux points géométriques : dans l’axe du faisceau central et 10cm en dehors. La dose a été constante dans les deux points géométriques. Fraction de survie, nombre de cassures double-brin et niveaux