Abstract
Introduction The quality of the dosimetric calculation is directly related to computerized calculation model and its operating parameters of the irradiation. The toughest conditions affect areas containing air cavities such as sinuses. Outside the Monte Carlo method, no other model correctly reproduces the dose distribution. The film dosimetry combined with the use of an anthropomorphic phantom help to assess the exact isodoses positions Material and methods A head phantom, dedicated to this study is voluntary cut in coronal planes passing through the air area cavities that were hollowed out. The film is constructed with EBT3 sensitive layer sandwiched between two plastic films. The shapes of the cavities are laser cut so as to accurately reproduce the contours. Laser cutting allows, at the same time to weld the two edges of the two plastic films and thus to maintain the sensitive layer in normal.The evaluation method was to compare dose distributions without cutting and with cutting, respect to the calculation, for a fixed rectangular irradiation (dimension 10 × 12 cm2) and a modulated irradiation arc therapy Results Laser cutting edge creates a film of constant quality. Soldering is uniform and effective. Comparison of dose distributions using the gamma index does not provide a useful analysis because of the very important differences. The comparison with profiles provides an information on the actual dose in the first few millimeters at the edge of the cavities. The uncut part of the film contributes to change the dose measurement in the first millimeters. So, cutting optimizes the measurement conditions. Comparison with the calculations brings provisionally useful information for potential clinical judgment. Conclusion The method of laser cutting the EBT3 film is effective. The measurement is accurate and reflects the dose distribution at the edge of the cavities. Perspectives: Measurements of cut films will be compared to a Monte Carlo calculation.
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