Plasma antioxidant substances apparently do not influence the radiodermatitis occurrence

RESULTS: No significant differences were observed in terms of TBARS and FRAP in plasma harvested from these patients at the beginning and at the middle of the treatment. There was lower incidence of grade two radiodermatitis among patients undergoing radiotherapy with hypofractionated doses. There were no differences in FRAP or TBARS among patients who developed radiodermatitis of any degree in relation to those who did not develop this side effect. No differences of FRAP or TBARS were observed between patients that presented grade two radiodermatitis regarding to the others studied.


Introduction
The cancer's world prevalence has increased in recent years, largely because of aging and the population growth, associated mainly with a lifestyle influenced by some already known carcinogenic factors such as smoking and sedentarism [1]. Worldwide, breast cancer is the most Moreover, it is estimated that in 2020 will be 66280 new cases of breast cancer in Brazil [2,3].
Radiotherapy (RT) has a pivotal role in the treatment of breast cancers. In the meta-analysis named EBCTCG (Early Breast Cancer Trialist's Collaborative Group), women underwent mastectomy and axillary emptying (with one to three affected lymph nodes) that were treated with RT after surgery showed a drastic reduction in locoregional recurrence rates and survival, either associated with chemotherapeutic treatment or not. According to this meta-analysis, RT is a fundamental part of the treatment to guarantee good results [4,5].
In our Department, the radiotherapy treatment is all guided by computed tomography (CT) images.
After the delimitation of both the tumor and the normal structures around it, the doses are planned through calculus software. However, even with this technical planning, RT's side effects cannot be discarded. Side effects produced by radiation are classified in acute and chronic. Acute side effects are those that occur during treatment or up to 90 days after initiating it. One of the main acute side effects of breast cancer is radiodermatitis. This effect is triggered by ionizing radiation-induced intracellular alteration. These radiation-induced intracellular alterations are either direct or indirect, upon molecules of deoxyribonucleic acid (DNA) [6]. Actually, tissues have different levels of radiosensitivity [7].
Radiation-induced direct effects, which correspond to a quarter of the damage produced in cell macromolecules, occur through collision of the photon with the DNA molecule, what breaks its double-strand. Radiation-induced indirect effects, responsible for most of the cellular damage, involves free radicals produced by the breakdown of hydrogen bonds of water molecule. Since water represents about 80% of the intracellular environment, the huge amount of free radicals that are produced in consequence of radiation causes a redox imbalance in the cell. As a consequence of this imbalance, it occurs cellular damage not only in the tumor but also in healthy tissues, thereby leading the side effects of the treatment. One of the most lethal radiation-induced modifications to the cells occurs in consequence of the reaction of free radicals with DNA that leads breakdown of its double-strand [6,[8][9][10][11][12][13].
On the other hand, free radicals are also products of the metabolism and have physiological functions such as phagocytosis, blood pressure control, cell signaling and apoptosis. However, in excess, they may cause cell damage by binding to constituent macromolecules such as carbohydrates, DNA, proteins and lipids. To keep under control the free radicals levels, there are antioxidant mechanisms in the body. Nevertheless, when the production of free radicals exceeds the capacity of the antioxidant defenses, it is established a pathophysiological condition called oxidative stress that leads to cellular damage [14].
The body's antioxidant defenses can be divided into enzymatic and non-enzymatic. The non-enzymatic defenses are due the presence of substances such as uric acid, vitamin C and albumin, that confer antioxidant properties to the body's fluids [15]. There are methods to evaluate the "antioxidant potency" of these non-enzymatic defenses present in biological fluids. One of these methods, FRAP (ferric reducing ability of plasma), is the determination of the plasma's ability to reduce the ferric ion (FeIII) to ferrous ion (FeII). Uric acid and vitamin C exert respectively 60% and 20% of the antioxidant capacity evaluated by this method [14][15][16]. The FRAP provides more biologically relevant information than the isolated dosing of the substances that make it up. This method is considered inexpensive, the reagents are simple to prepare, the results are highly reproducible and the procedure is simple and fast. For these reasons the FRAP has been increasingly used in research of oxidative stress and its effects [14]. However, this method has some limitations because not every antioxidant can reduce the ferric ion and not every substance present in the plasma, capable of reducing the ferric ion, is an antioxidant. In addition, FRAP measures only non-enzymatic antioxidant defenses [14,16]. In parallel, there are also techniques for

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the quantification of oxidative stress. The body undergoes oxidative stress generates high levels of lipid peroxidation products, such as lipid hydroperoxide, malondialdehyde (MDA) and nitric oxide metabolites. One of the most used technic of quantification of oxidative stress is the TBARS (thiobarbituric acid reactive substances) [17,18].
This method quantifies the concentration of MDA in the medium by spectrophotometry [14,16].

Study type
Prospective cohort study, conducted at the Department of Radiotherapy and Oncology, in

Inclusion criteria
Patients with a diagnosis of breast cancer, without previous RT treatment, including those underwent adjuvant RT, with or without partial or radical mastectomy. The study had no restrictions of age, gender or ethnicity.

Exclusion criteria
Patients with a history of previous treatment for any other neoplasia, renal failure, liver dysfunction and/or heart failure, as well as those with metastatic disease.

Radiotherapy procedure
RT was performed using the three-dimensional (3D) technique, with a 6mV photons beam. All cases were submitted in the CT simulation, with initial tumor volume evaluation. CT was acquired with 3mm cuts, from the cricoid cartilage up to the L3 vertebra. In planning the breast was circumvented, as well as the lymphatic drainage and organ at risk such as heart, lungs, esophagus and thyroid. In cases of mastectomy, the

Plasma constituents that determine FRAP
In the present study, it was also necessary to know the plasma concentrations of uric acid, vitamin C, albumin and hemoglobin, since these constituents that determine the FRAP values. Plasma levels of uric acid, albumin and hemoglobin were obtained from the routine hospital service.

Radiodermatitis assessment
During RT treatment, the nursing team performed evaluations in order to detect side effects (radiodermatitis) and their degrees. All patients underwent at least three evaluations by the nursing team during treatment to detect radiodermatitis and its degrees. The radiodermatitis grading was guided by the CTCAE 4.03 (Medical Dictionary for regulatory Activities; MedDRA v12.0 Code 10061103, Dermatitis radiation) [20]: • Grade one: Faint erythema or dry desquamation; • Grade two: Moderate to brisk erythema; patchy moist desquamation, mostly confined to skin folds and creases; moderate edema; • Grade three: Moist desquamation in areas other than skin folds and creases; bleeding induced by minor trauma or abrasion; • Grade four: Life-threatening consequences; skin necrosis or ulceration of full-thickness dermis; spontaneous bleeding from involved site; skin graft indicated.

Systematics of data collection
After identifying the cases eligible for the study and application of the informed consent form, the following data were collected: age, gender, ethnicity,      The values of TBARS, obtained at the beginning, in the middle and at the end of the RT treatment, also did not differ significantly in patients who presented radiodermatitis in relation to those who did not. There were also no differences in TBARS, determined along the RT treatment, among patients who developed grade two radiodermatitis compared to the others ( Table 4). or at the end of treatment ( Table 5). There was also no statistical difference in these parameters, determined at the beginning, middle or at the end of treatment, among patients with ages greater than and less than 60 years ( Table 6).  In the present study, few patients needed an- One of the most used treatments for breast tumors is RT. This modality of treatment, is fundamental to increase the survival of these patients [4,5]. However, although considered less invasive, the RT is not free of adverse effects. It is known that approximately 90% of women submitted to RT for breast cancer have skin changes during treatment [31]. This is the reason why we decide to study patients affected by this type of cancer. In the present study, 60.9% of the followed up patients developed radiodermatitis during treatment, an incidence slightly lower than the reported by the literature [32]. Nevertheless, radiodermatitis is still the main collateral effect among these patients. In the present study, no significant modifications of TBARS were observed along the RT treatment.

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This suggests that the systemic redox balance was maintained in these patients, despite the RT effects. These data, however, require a careful analysis because several studies suggest that radiation increases the oxidative stress in different tissues [11,12]. What it can be stated is that, at least in these patients, the local oxidative stress did not lead to a systemic redox imbalance that could be we also evaluated lipid peroxidation in patients younger than 60 years, separately from those older than 60 years. This is because, as we know, aging is a condition characterized by an increase in oxidative stress [40,41]. However, in any of the age ranges we do not observe any significant modification of TBARS.