ABSTRACT
Introduction: Breast cancer is the
most common cancer in women. The treatment of breast carcinoma has advanced in
the last decade and nowadays there are treatment protocols for all stages of the disease. Depending on the
histopathology and stage breast cancer is treated with surgery, chemotherapy
and radiotherapy. Regarding radiation, the field of irradiation includes the
chest wall in patients with mastectomy, or the breast glandular tissue in
patients with conserving surgical approaches. It is often treated with
radiation therapy with two opposing
tangential fields, and when indicated supraclavicular lymph nodes have
to be irradiated. In this case an additional anterior field is applied. The
tangential as well as the other radiation beams have a potential damaging effect on the healthy surrounding
tissues, particularly over the heart in the left breast irradiation and
in the lungs as well. Material and Methods: The study included 25
patients with left breast carcinoma, all post surgery, treated with radiation
therapy, with the Elekta accelerator at our department. For academic purpose
the treatment plans were generated following two methods. The first one with
two tangential opposite beams plus a supraclavicular beam. In this method the
angles of the tangential internal and external create an angle that is equal to 180˚{310˚ &
130˚}; no further changes were made to the beam geometry. Even though this
is not the best option from the dose distribution point of view, it is still
the most applied method, probably because of the semplicity of it. For each
patient, a second plan was generated using two opposite tangential beams plus the
supraclavicular beam. The angles of the internal and external beam were changed
from 1˚ to 3˚, depending on the surface of the body, so that the resulting
angle was 180˚ ± 3˚ {310˚± 3˚& 130˚ ± 3˚} with
the aim to adapt the beam geometry as much as possible to the shape of the
thoracic wall and to spare the OAR-s. Results and Discussion: The data
show that the dose in the organs at risk, in terms of dose percentage, is lower
when the angles of the beams are changed with 1˚ - 3˚, compared to the classic
method where the internal and external angles equal 180˚. This dose is not only
non-negligible but significant; for every angle change from 1˚to 3˚, there is a
significant reduction in the integral dose in the radiated volume, expressed in
percentage, up to 5%. Conclusion: In most centers, the radiation
treatment of breast is realized with two tangential opposite beams, which
usually are mirror beams, or in other words, the internal and external beam
angles create an angle of 180˚{α + β = 180˚}. This is a simple method,
which provides a good dose distribution, but leaves a relatively high dose in
the organs at risk. This study shows the difference in the dose percentage in
the heart and lung when the beam angles are changed adapting to the anatomy of
the patient. Reducing these doses allows for better overall treatment and less
longtime toxicity, particularly for the heart tissues.