Supervisors info:
Άννα Ζυγογιάννη, Επίκουρη Καθηγήτρια, Ιατρική Σχολή, ΕΚΠΑ
Χρήστος Αντύπας, ΕΔΙΠ, Ιατρική Σχολή, ΕΚΠΑ
Χριστίνια Αρμπιλιά, ΕΔΙΠ, Ιατρική Σχολή, ΕΚΠΑ
Summary:
Purpose: The purpose of this study is to calibrate the Gafchromic EBT – XD films, that are newly introduced to the radiotherapy department, in order to be used in clinical practice at the department, and to compare them with the Gafchromic EBT3 films. Furthermore, the dosimetric characteristics of grid radiotherapy were investigated through the TPS and the Gafchromic EBT – XD film.
Methods and Materials: Firstly, the Gafchromic EBT3 films were calibrated, even though they are commonly used in the department, in order to become familiar with the procedure and the calibration protocol. Then, the Gafchromic EBT – XD film was calibrated. The two calibration methods were compared both in accordance to the protocol used, and the handling of both types of films. In addition to this, a treatment plan was created to simulate a grid radiotherapy plan. The prescribed dose at the peaks was 10 Gy at 10 cm depth. The plan was executed on a solid water phantom that had an EBT – XD film placed at 10 cm depth. The similarities and differences between the TPS and the EBT – XD film were studied, and also the valley-to-peak ratio was calculated for both the TPS and the EBT – XD film. Finally, an error that occurred with the MLC, during the radiation, was evaluated. The error that occurred was that in three parts of the plan, the MLC did not fully close its leaves.
Results: Both methods of handling and calibrating the EBT3 and EBT – XD films are similar, with their only difference in the dose range. Both calibration curves are described by a fourth degree polynomial. The EBT – XD film shows lower sensitivity and measures lower optical densities in comparison to EBT3, in the latter’s range of function. The EBT – XD film showed with success the prescribed dose of 10 Gy in the grid radiotherapy plan, while the TPS showed lower values. The difference between both of them is almost constant in the different dose profiles and is smaller in the center of the plan. The valley-to-peak ratio, which is calculated from the TPS is the same as the one calculated by the EBT – XD film, and both of them are in the limits that are expressed in the literature, even for the three parts, where the MLC did not fully close its leaves.
Conclusions: The introduction of the Gafchromic EBT – XD films does not require any special handling that the personnel is unfamiliar with. On the contrary, the procedure is similar with the EBT3 films and they can be used in addition to EBT3, for higher doses. In that way, the needs of a modern radiotherapy department are covered. In the grid radiotherapy treatment plan, the dosimetric characteristics were evaluated and were found to be in accordance to the literature. The MLC, that did not fully close its leaves, strongly suggests the use of an in vivo dosimeter, like the aforementioned films, when a treatment like this is executed.
Keywords:
Dosimetry, EBT3, EBT – XD, Grid radiotherapy, Valley-to-peak ratio
