A verification methodology for in vivo dosimetry in stereotactic radiotherapy

Radiotherapy of brain lesions near critical structures requires a high accuracy in the location and dose. The high precision is achieved by the location of the stereotactic apparatus. The accuracy in dose delivery should be accompanied by an accurate quality control in devices that involve the practice, however, still does not guarantee the dose at the time of therapy. The large number of fields and the small size of these conventional methods difficult dosimetry during treatment. The objective of this work was to develop a verification methodology in vivo dosimetry in stereotactic radiotherapy with the aid of the film radiochromic Linear Accelerator with multi leaf collimators Moduleaf. The technique uses film segments radiochromic Gafchromic EBT2, with dimensions of 1x1 cm2 in area outside the coupled micro-multileaf Moduleaf Siemens. These films were inserted in the region of the central axis of the beam. The films were irradiated and calibrated to obtain the factors that determine the size dependence of the dosimetric field. With these data, we designed a computer program which calculates the density of a film must acquire when subjected to an exposure in this setting. This study evaluated five non-coplanar plans, the first with 15 fields and the other with 25 fields. Before starting the procedure, the film segment is coupled to the device, and after the treatment, the relative density is evaluated and compared with the calculated. The average value of the verification at the time of radiation dosimetry compared with the calculated by the sheet was 1.5%. The data collected in this study showed a satisfactory agreement between measured and calculated by the program in the densitometer. Thus, a methodology was developed to verify in vivo dosimetry in radiotherapy and stereotactic linear accelerator collimators Moduleaf. (author)