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Review of the energy check of an electron‐only linear accelerator over a 6 year period: Sensitivity of the technique to energy shift
Author(s) -
Biggs Peter J.
Publication year - 2003
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.1560891
Subject(s) - linear particle accelerator , timer , calibration , flatness (cosmology) , energy (signal processing) , thermoluminescent dosimeter , physics , monitor unit , sensitivity (control systems) , optics , particle accelerator , metric (unit) , beam (structure) , computational physics , computer science , mathematics , radiation , statistics , nuclear medicine , dosimeter , computer hardware , electronic engineering , engineering , medicine , cosmology , quantum mechanics , microcontroller , operations management
The calibration and monthly QA of an electron‐only linear accelerator dedicated to intra‐operative radiation therapy has been reviewed. Since this machine is calibrated prior to every procedure, there was no necessity to adjust the output calibration at any time except, perhaps, when the magnetron is changed, provided the machine output is reasonably stable. This gives a unique opportunity to study the dose output of the machine per monitor unit, variation in the timer error, flatness and symmetry of the beam and the energy check as a function of time. The results show that, although the dose per monitor unit varied within ±2%, the timer error within ±0.005 MU and the asymmetry within 1–2%, none of these parameters showed any systematic change with time. On the other hand, the energy check showed a linear drift with time for 6, 9, and 12 MeV (2.1, 3.5, and 2.5%, respectively, over 5 years), while at 15 and 18 MeV, the energy check was relatively constant. It is further shown that based on annual calibrations and RPC TLD checks, the energy of each beam is constant and that therefore the energy check is an exquisitely sensitive one. The consistency of the independent checks is demonstrated.