Differences in Dosimetric Performances of Compared URT-Linac 506c with TrueBeam
Y Liang*, L Yu, B Yang, T Pang, X Liu, J Qiu, Peking Union Medical College Hospital, Beijing, BeijingCN,
Presentations
PO-GePV-P-7 (Sunday, 7/10/2022) [Eastern Time (GMT-4)]
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Purpose: uRT-linac 506c (United-Imaging Healthcare, China) is a sort of CT-linac, which coalesces of FBCT and O-ring gantry accelerator. Meanwhile, TrueBeam (Varian Medical System, USA) has kV and MV CBCT system with 4 photon energies and several electron energies. Though both of them have 6X, 6XFFF photon energies, their difference in dosimetric performance may leads to inaccuracy during the IMRT and VMAT processes. The aim of this study is to explore the difference on monitor unit linearity, output constancy vs dose rate and gantry angle, repeatability and daily stability.
Methods: As proposed in AAPM TG142 report, Max4000 electrometer, FC-65G ionization chamber and Solid water are used in dosimetric performance test, including monitor unit linearity, output constancy vs dose rate. Meanwhile, A12 ionization chamber was placed in front of treatment couch, in the middle of table, which could measure output constancy in different gantry angle.
Results: Both in 6X (400MU/min) energy, the result indicates uRT-linac 506c has -2.18% deviation monitor unit linearity, while 3.93% in TrueBeam. Lower output brings out when the dose rate gets higher in uRT-linac 506c, ranging from -0.31 % to -0.53%. Output stabilization in TrueBeam gets much better, from -0.34% to 0.11%. As for the gantry angle effects on output constancy, uRT-linac 506c rises to 0.6% since its rotation angle of one cycle is 540°. TrueBeam shows lower deviation of -0.19%, whose angle of one revolution is 360°. With regard to repeatability and daily stability, there was no significant difference of these two linacs.
Conclusion: Since the excellent property on monitor unit linearity, uRT-linac 506c may have advantages on small segment dimensions, but the output change caused by dose rate should raise concern in clinical protocols. Simultaneously, TrueBeam output constancy relies less on dose rate and angle of rotation, which is of immense benefit to VMAT delivery.
Keywords
Dosimetry, Ionization Chamber, Linear Accelerator
Taxonomy
TH- Radiation Dose Measurement Devices: ion chamber: air cavity
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