Dosimetric Verification Using 2D Planar Diode Arrays and 3D Cylindrical Diode Arrays in IMRT and VMAT

Introduction: Dosimetric verification of intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) before treatment is necessary due to the complexity of delivery beams. This work aims to evaluate the performance of 2D planar and 3D cylindrical diode arrays for patient specific QA in IMRT and VMAT. Methods: MapCHECK and ArcCHECK were studied for their properties before clinical use. The clinical performance was demonstrated with IMRT and VMAT plans, the measured results were compared with the calculation from Eclipse treatment planning. The gamma index of 3% /3mm with 10% threshold dose were the criteria of agreement between measured and calculated. Results: MapCHECK and ArcCHECK showed linearly dose response and demonstrated a short term and long term reproducibility within ± 0.2 and ± 2%, the repeatability rate effect was within ± 0.1 and ± 0.25 %, respectively. The dose rate response was within ± 1% for both detectors. The field size dependence was the same as ionization chamber response. The variation in energy response was within ± 4.5% for MapCHECK and ± 2% for ArcCHECK. The measured beam profile of open and 30° of hard and enhance dynamic wedge showed good agreement with calculated dose. Both detectors showed the excellent percentage passing for all 15 IMRT and VMAT plans. For IMRT, The average of the % pass of MapCHECK was 97.31 with the mean gamma of 0.45. The average number of detector was 344.80, while the average of the % pass of ArcCHECK was 97.21 with the mean gamma of 0.46. The average number of detector was 1049.31. For VMAT, The average of the % pass of MapCHECK was 98.55 with the mean gamma of 0.37. The average number of detector was 410, while the average of the % pass of ArcCHECK was 97.04 with the mean γ of 0.43. The average number of detector was 1054. Discussion: The more detectors of ArcCHECK than MapCHECK make more dose measurement points that increase the chance of dose difference. In addition, MapCHECK is a planar geometry which cannot detect high dose gradient in the sensitive area in some gantry angle, while ArcCHECK is a cylindrical geometry which can measure dose distribution for all gantry angles, so less point missing attributed to more dose difference. Conclusions: Both detectors have excellent performance for IMRT and VMAT verification, however, the characteristics of the devices should be studied before clinical used.