DOSIMETRIC COMPARISON OF PATIENT SPECIFIC QA IN LUNG SBRT USING UNFLATTENED BEAMS BETWEEN TWO DOSIMETER SYSTEMS

Abstract

In advance technique, the patient specific QA tool needs more accurate dose measurement. The purpose of this study is to determine the dosimetric difference of two dosimeter systems in VMAT lung SBRT. The patient specific QA tools were performed in IBA CC13 in ArcCHECK, IBA CC13 and CC01 in Lucy phantom for point dose and diode array detectors in ArcCHECK and EBT3 film in Lucy phantom for dose distribution in fifteen VMAT lung SBRT plans using unflattened photon beams. All measurements were performed with 6MV FFF photon beam from Varian TrueBeam linear accelerator and the plans were generated using the Varian Eclipse treatment planning system and Acuros XB algorithm (version 11.0.31). For point dose verification, the measured dose and calculated dose were compared by percent point dose difference with criteria ±3% for control limit and ± 5% for action limit. For dose distribution verification, the measured dose and calculated dose were compared by percent gamma pass of 3% dose difference and 3 mm distance to agreement with 10% threshold. The criteria were above 90%. For the results of point dose difference, the mean percent point dose difference were -1.3±2.3%, -0.7±2.3% and -1.4±1.8% for CC13 in ArcCHECK, CC13 in Lucy phantom and CC01 in Lucy phantom, respectively. The point dose difference between CC13 in ArcCHECK and CC13 in Lucy phantom was not statistical significant difference with p-value = 0.5. And the point dose difference between CC01 and CC13 in Lucy phantom also was not statistical significant difference with p-value = 0.4. For dose distribution verification, the mean percent gamma pass were 94.9±1.9% and 92.6±5.9% for diode array detector in ArcCHECK and EBT3 films in Lucy phantom. The gamma pass between diode detector array in ArcCHECK and EBT3 film in Lucy phantom was not statistical significant difference with p-value = 0.2. From the results, the dose differences between calculation and measurement for almost all of the cases were within criteria of ±3% point dose differences or 90% gamma pass for dose distribution differences. The effect on chamber and phantom were not statistical significant difference. However, some dosimeters have limitation for using, the characteristics of dosimeter should be studied before performing the measurement.