DOSIMETRIC INVESTIGATION OF RADIOTHERAPY OF SMALL SIZE TUMORS IN RADIOSURGERY DEVICES

Abstract

In stereotactic radiotherapy, high radiation doses were delivered to tumors using small fields in 1-5 fractions. It is very important to make sure accuracy of dose and position of given dose in stereotactic radiotherapy. In this study, dosimetric measurements of small sized brain tumors irradiated in CONE- based linear accelator (linac) and the volumetric arc therapy (VMAT) linac modalities were performed with EBT3 film. 1,2 and 3 cm diameter tumors were virtually created in Cyberknife head and neck phantom. Gafchromic EBT3 film was placed into the phantom to evaluate the accuracy of the doses given. The phantom was irradiated with Gafchromic EBT3 film according to treatment plans created in the treatment planning system of two separate devices for each tumor size. Conformity Index (CI) and Homogeneity Index (HI) were calculated for the quality of created treatment plans. The dose distributions calculated in the film and the TPS were compared. When the CI and HI values were examined, the CI and HI values of the cone-based linac device were close to 1. The EBT3 measurement results indicate that all SRT treatment modalities achieved accurate doses. According to results, if a critical organ, such as the brainstem, is located near the tumor and the situation requires a steep dose gradient, the cone-based linac should be used for SRT therapy. This study has shown that on CONE-based linac or VMAT-based linac devices can be used instead of each other in small-area irradiations.