Yoğunluk Ayarlı Radyoterapi Tekniğinde İn Vivo Dozimetri İçin Elektronik Portal Görüntüleme Sistemi ve Diyot Dedektörlerin Kullanılması

Abstract

Intensity Modulated Radiation Therapy (IMRT) is an advanced method of three-dimensional conformal radiotherapy techniques. Patient-specific quality assurances are very important for IMRT technic. These assurances are often performed pre-treatment. However, the anatomy of the patient can be change during the treatment related to weight loss or edema. Thus, pre-treatment quality assurance are inadequate at this point and in-vivo measurements are required. In this study, diode detectors and electronic portal imaging system (EPID) were investigated for in-vivo dosimetry in IMRT. 10 treated head and neck patients' IMRT plans have been selected for the diode measurements. At the same time, all these 10 dynamics IMRT plans were transformed into the static IMRT so we obtained 20 IMRT plans. In the next step, 20 IMRT plans moved on universal phantom individually and recalculated. Then we have measured the doses with diodes and ion chambers. The diode and ion chamber measurements have been compared with the doses that achieved from treatment planning system (TPS). The results showed that diodes can be used for in-vivo dosimetry in static and dinamic IMRT. Also, diode measurements have been tested on Alderson Rando® phantom which has a closer stucture with human anatomy. These measurements are compatible with universal phantom measurements. However, based on our experience, we suggest that the location of the diodes must be done carefully on patient or Rando ® phantom due to the dose gradients. In thıs study EPID was used to measure transmitted radiation. The transmitted radiation have been measured on 1, 15, and 33th fraction and analyzed with each other using gamma method. As a result of gamma analysis it has been seen that there is a relationship between the gamma result and the patient's weight loss and thinning of the patient neck. Results showed that EPID can be used to detect the errors between fractions for IMRT. In our study we have mesured the transmitted doses in terms of workload in every 15 days but we suggest that measuring the doses in every 5 days to detect the errors on time.