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Technical Note: Vendor miscalibration of preclinical orthovoltage irradiator identified through independent output check
Author(s) -
Chen Quan,
Carlton Drew,
Howard Thaddeus J,
Izumi Tadahide,
Rong Yi
Publication year - 2021
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 - 10.1002/mp.14642
Subject(s) - dosimetry , calibration , ionization chamber , monte carlo method , ionization , vendor , backscatter (email) , nuclear engineering , computer science , nuclear medicine , medical physics , environmental science , materials science , physics , medicine , mathematics , engineering , statistics , telecommunications , ion , quantum mechanics , marketing , business , wireless
Purpose Accurate radiation dosimetry in radiobiological experiments is crucial for preclinical research in advancement of cancer treatment. Vendors of cell irradiators often perform calibration for end‐users. However, calibration accuracy remains unclear due to missing detailed information on calibration equipment and procedures. In this study, we report our findings of a vender miscalibration of the radiation output and our investigation on the root cause of the discrepancy. Methods Independent calibration verification for a commercial preclinical orthovoltage irradiator was conducted. Initially, in the absence of ionization chambers calibrated at kV energy, radiochromic films (EBT3) was first calibrated at MV energy. Energy correction factors from literature were used to create an in‐house kV dosimetry system. The miscalibration identified with the in‐house kV EBT3 dosimetry was later confirmed by ADCL calibrated ionization chambers (Exradin A1SL and PTW 30013) at kV energy. Ionization chambers were suspended in‐air following TG‐61 recommendation for output calibration. To investigate the root cause of the miscalibration, additional measurements were performed with ionization chambers placed on the shelf. A validated Monte Carlo simulation code was also used to investigate the impact of placing the ionization chamber on the shelf instead of suspending it in air during the vendor‐performed calibration process. Results Up to a 6% dosimetry error was observed when comparing the vendor calibrated output of the preclinical irradiator with our independent calibration check. Further investigation showed incorrect setups in the vendor’s calibration procedure which may result in dose errors up to 11% from the backscatter of the shelf board during calibration, and up to 5% from omitting temperature and pressure corrections to ionization chamber readings. Conclusion Our study revealed large dose calibration errors caused by incorrect setup and the omission of temperature/pressure correction in the vendor’s calibration procedure. The findings also highlighted the importance of performing an independent check of the dose calibration for preclinical kV irradiators. More absolute dosimetry training is needed for both vendors and end users for establishing accurate absolute dosimetry.