Comparison of patient specific quality assurance tests for SRS/SBRT treatment plans using different dosimetric systems

"Comparison of Patient-Specific Quality Assurance Tests for SRS/SBRT Treatment Plans Using Different Dosimetric Systems", Trakya University, Institute of Health Science, Health Physics Department, Master / Thesis, Edirne, 2024. Background and Aim: With today's technological developments, the frequency of use of complex treatment techniques such as intensity modified radiotherapy (IMRT) and volumetric arc therapy (VMAT) has increased considerably. These developments in both treatment devices and imaging systems have enabled the stereotactic application of significantly higher treatment doses to the patient in a single or small number of fractions compared to previous conventional fractionations. In these treatment schemes called stereotactic radiosurgery (SRS) and stereotactic body radiotherapy (SBRT), it is strongly recommended that patient-specific quality assurance tests be performed before the dose distributions calculated in the treatment planning system (TPS) are given to the patient in the treatment device. In this study, it was aimed to evaluate the dose responses of the ArcCheck dosimeter system, which has portal dosimetry (Electronic Portal Imaging Device/EPID) and circularly arranged multiple diode detectors, according to different gamma index evaluation criteria, in patient-specific quality assurance tests for SRS/SBRT treatment plans and to compare the results. Material and Methods: For this purpose, the dose distributions of 30 patients from different disease groups planned to be treated with SRS/SBRT treatment schemes and the results obtained by measuring the quality assurance tests required before treatment separately in EPID and ArcCheck detector systems were compared with the dose distributions calculated in TPS using the gamma index method. . During the comparisons, the gamma index criteria were dose difference and distance to agreement (DTA), respectively: 3-3% mm, 3-2% mm, 2-3% mm, 2 2% mm, 2-1% mm, 1-2% mm and 1-1% mm criterias were used. Then, the differences between the two dose distributions were calculated according to each gamma index evaluation criterion and gamma index passing rates (GPR) were found. Results: In the results obtained, according to the 3-3% mm, 3-2% mm, 2-3% mm and 2-2% mm gamma index criteria, the GPR values obtained from EPID and ArcCheck detectors, viii respectively were 98.54±2.20%; 97.66±0.63%; 97.22±3.90%; 92.26±16.98% and 99.60±0.33%; 98.34%±0.20; 99.17±0.58%; 97.01±1.69%. It has been observed that there is no significant difference in these criteria between the results of two different measurement systems. However, when the evaluation criteria were reduced to 2-1% mm, 1-2% mm and 1 1% mm, significant differences were observed in the GPR results of both detectors. Conclusion: All dosimetric systems used in quality assurance tests of patients in RT have different features and different spatial resolutions. It may be possible to increase the quality of treatment for the patient by using detectors that can detect errors that may occur during treatments in advance. For this reason, it is recommended to know exactly the characteristics of the dosimetry system to be selected and used and to compare measurement results with different dosimetric systems when necessary. Additionally, in order to obtain accurate quality assurance tests, the selection of gamma tolerance limits should be specific to each clinical treatment site and detector used. Keywords: Stereotactic radiosurgery (SRS), stereotactic body radiation therapy (SBRT), Patient-specific quality assurance test, portal dosimetry, ArcCheck