Dose Variation Profiles of Small Fields with a 10 MV Photon Beam

Abstract

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.