Original article | International Journal of Innovative Approaches in Science Research 2020, Vol. 4(3) 66-83
pp. 66 - 83 | DOI: https://doi.org/10.29329/ijiasr.2020.273.2
Published online: September 29, 2020 | Number of Views: 8 | Number of Download: 92
In breast cancer, electron energies are preferred over photon energies because they provide minimal lung exposure when conditions allow for thin chest wall irradiation after mastectomy. In patients with irregular chest wall, it is difficult to perform a homogeneous irradiation with fixed electron beam therapy due to reasons such as thickness differences, irregular contour and lack of tissue, long scar and area joint problems. Electron arc therapy is propose as an alternative method in such patients.
The study was carried out with electron energies of 6, 9, 12, 13.5 and 16 MeV. First, in order to be able to use it in electron arc planning in the planning system, after determining the dose characteristics of all available electron energies of the electron arc technique, the accuracy of these dose distributions was verified with film and TLD dosimetry. After the suitability was determined, electron arc plans were made on the CT simulation image of 20 patients selected due to the difficulty of homogeneous irradiation with the classical method.
While the chosen reference dose of 85% covered the PTV homogeneously, it was found that the dose was decreased by an average of 50% compared to photon and classical electron therapy in the examination performed in terms of radiation dose to which the lung volume was exposed. During the planning, a homogeneous dose and bolus of different thicknesses were required depending on the energy in most patients to regulate the reduction in surface dose depending on the arc angle. Bolus prevents the lung and heart from overdosing while ensuring that the dose in the deeper parts of the target volume is more uniform. The use of tertiary block in electron-arc dose distributions prevented unwanted dose reduction in the field edges and provided a more homogeneous dose distribution at 85% reference isodose. If the structure of the patient's contour is very irregular, the dose distribution is not smooth due to the depth difference.
In this context, it has been determined that during optimization, the isocenter depth should be chosen for the homogeneity of the dose distribution and to be as equal as possible from the surface at all beam angles. In addition, in the study, it was determined that more appropriate dose distributions were obtaine when the isocenter depth is greater than the maximum reach of electrons. Even if multiple electron fields of different energies are used, more homogeneous dose distributions have been achieve by eliminating field combination problems with the use of electron arc therapy.
Keywords: Breast cancer, treatment with electron beams, Electron, electron arc, chest wall, dose optimization
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