Can Dynamic Conformal arc be an Option in Epidermoid Cervical Cancer Treatment?

Historically locally advanced cancer of the cervix has been treated with radiotherapy and brachytherapy and it was not until 1999 that the use of concurrent chemotherapy was formalized due to excellent results in terms of rate of overall and disease-free survival. Box technique in radiotherapy is the most widely known providing excellent results, with some variations as oblique fields, but greatly increasing irradiation potentially healthy tissue, leading to the higher proportion of own side effects of each treatment. Therefore present a radiant treatment planning mode Dynamic Conformal Arc for cervical carcinoma.Treatment with dynamic conformal arc achieves better conformation of tumor and area to be treated, avoiding unnecessary doses to organs at risk (OAR), compared to conventional four fields irradiation technique (box technique), further significantly reduces the treatment time.Dynamic Conformal Arc (DAT) technique in the pelvis reduces irradiation dose in the organs at risk, making a good coverage of the clinical area to be treated, further decreasing the side effects. It could be considered as an alternative to conventional treatment of 4 fields or to the impossibility of intensity modulated radiation therapy (IMRT).


Introduction
Worldwide, cervical cancer is the fourth most common female malignancy in both incidence and mortality, resulting in approximately 527,600 new cases and 265,700 deaths annually [1,2]. Currently among the female population of Dominican Republic, cervical and breast cancer disputed the first and second place, statistics that resemble those seen in other developing countries in Latin America and the Caribbean. The high burden of cervical cancer in developing countries reflects the absence of cervical cancer prevention programs. The majority of the incident cases and deaths from cervical cancer, occur in developing countries, where resources for early detection and treatment are severely limited [3][4][5].
Cervical cancer and precancerous lesions behave as a sexually transmitted disease, especially associated with infection by the human papillomavirus (HPV), this being the causative agent of this disease in ˃99% of cases [6,7].
The definition of locally advanced cervical cancer, include patients with stage IB2 to IVA (Table 1). Surgery is not a therapeutic option for patients with stage IIB, III and IV due to a high proportion of positive margins and high risk factors for recurrence. External beam radiation therapy with chemotherapy plus brachytherapy has been, so far, the treatment of choice for patients with locally advanced cervical cancer [8][9][10][11].

Patient
Female patient 68 years old with a history of hypertension, who was referred to the National Cancer Institute Rosa Emilia Sánchez de Tavares (INCART) Radiation Oncology Center (CRO) for radiation treatment concurrent with chemotherapy.
The patient refered genital bleeding and pain, so go to doctor who performs studies including biopsy, which concluded: squamous cell carcinoma moderately differentiated, infiltrating, therefore requested CT pelvis with contrast, in which large mass cervicalwas evidenced, with extension to the uterine myometrium, associated with dilated endometrial cavity (with approximate dimensions 66mm anteroposterior diameter) with sero-hematic contained therein, with slight irregularity of the serosa of the cervix, with subtle attenuation peripheral fat; turn left evidence obturator lymph nodes in region.

Pelvis CT and definition of the target volume and OAR
The patient was treated in the supine position, with support leg positioning to ensure reproducibility. The cervix, uterus, regional lymph nodes, bladder, rectum and sigmoid were defined [12,13]. We make treatment planning based on a CTV45.0_1.8 + 5mm margin and PTV45.0_1.8 + 5mm margin. Subsequently it was defined a PTV10.0_2.0, which was limited to the parametrium.

Settlement field
It has been proposed a technique of dynamic arcs (DAT) for its acronym in English: dynamic arc treatment, whose purpose is based on the PTV using multileaf collimation at all times when they are performing the angular displacements of the gantry (Figure 1). Therefore, to perform volume coverage planning have established two semi-arcs. The first arc with an angular displacement from 0° to 179° and the second arc of 179° to 359°. 100 control points were established for each 1.8 ° of displacement. Each checkpoint was assigned a weight of 0.0101. (Figure 2), the formation of the PTV was made with multileaf ( Figure 3).

Patient Positioning
The patient was checked every 3 days using portals fields each other orthogonal 10x10 cm² images and OBI. The structure of the pelvis was matched to the anatomy of the pelvis of digital radiography rebuilt.

Discussion
The Dynamic Conformal Arc plan compared with the conventional technique of box has two important advantages, including: dose and time ( Figure 4).

Dose
As shown in Figure 5 the 60% isodose technique box for tissue level reaches subcutaneous and obviously undesired dose to the patient, while for the DAT technique does not show the 60% dose in said area. Isodose reaching the subcutaneous tissue with DAT is 35%. Having a differential decrease of approximately 25% over the conventional field.
Furthermore, the conformity of dose PTV DAT technical box is smaller. The compliance rate for PTV box was 1.09 while for the DAT was 1.07.

Time
The total time for the each conventional fields was 2.02 minutes while for DAT it was 1.4 min total treatment.

Conclusion
Technological progress in radiation therapy in the last 30 years has many treatments available to patients that offer high-precision radiotherapy, with consequent reduced toxicity, increased doses to achieve greater tumor control and reduced irradiation time.