The increasing demand for CT scans in pediatric patients is mainly due to the high rates of traumatic injuries from car accidents, falls on bicycles, blunt trauma, traumatic brain injury, as well as a significant increase in the incidence of childhood neoplasms, being the CT images used in the diagnostic process. Therefore,

Radiotherapy is a treatment of carcinogenic tumors using ionising radiation and the improvement of radiotherapy techniques has been conducted to protection of healthy tissues. Recent implementations have employed static fields with small dimensions. The interests for this work were small fields, used in modern techniques such as Stereotactic Radiation Therapy (SRS) and Intensity Modulated Radiation Therapy (IMRT). These fields have special characteristics that refer to the non-establishment of the physical conditions idealized in traditional dosimetry protocols and localized imbalances of the photon spectrum. The obtained profiles allowed to verify disturbances present in the exposures, considering the dosimetry of small fields and the impacts on the planning of local dose deposition. In this work, the dose distribution of an X-ray beam was recorded using a solid water phantom. This phantom was irradiated using small fields with 1 × 1, 2 × 2, 3 × 3 and 5 × 5 cm 2 . The 10 MV X-ray beam was generated in a linear accelerator model Synergy Platform from the manufacturer Elekta and radiochromic film sheets were used to record dose profiles inside a solid water phantom. The solid water phantom loaded with radiochromic film was positioned 1m away from the X-ray beam's focus. The longitudinal profile of absorbed dose obtained presented the maximum dose value at 2.24 cm of depth for both fields, inside the phantom. Smaller field size generated a maximum absorbed dose smaller. The axial dose profiles were recorded at 1 cm depth, and presented a plateau in the axis Y for the four fields. For axial irradiation on the X-axis, the central region is 99.27% in relation to 100% of the relative dose and on the Y-axis, the central region is 99.39% in relation to 100% of the relative dose.

Computed Tomography (CT) is an efficient and non-invasive method to obtain data about internal structures of the human body. CT scans contribute with the highest absorbed doses in population due X-ray beam attenuation and it has raised concern in radiosensitive tissues. Techniques for the optimization of CT scanning protocols in diagnostic services have been developing with the objective of decreasing the absorbed dose in patient, aiming image quality within acceptable parameters for diagnosis by noise control. Routine head scans were performed using GE CT scan of 64 channels programmed with automatic exposure control and voltages of 80, 100 and 120 kV attaching the noise index in approximately 0.5%, using the tool of smart mA. Radiochromic film strips were placed into an anthropomorphic adult male phantom to measure the absorbed dose deposited in areas such as lens, thyroid and pituitary gland for study of dose deposited in these important areas containing radiosensitive tissues. Different head scans were performed using optimized values of mA.s for the different voltages. The absorbed dose measured by the film strips were in the range of the 0.58 and 44.36 mGy. The analysis of noise in the images is within the acceptable levels for diagnosis, and the optimized protocol happens with the voltage of 100 kV. The use of other voltage values can allow obtain better protocols for head scans.